path: root/xc/doc/specs/Xt/CH09

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.\" Digital Equipment Corporation, Maynard, Massachusetts.
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.sp 1
.ce 3
\s+1\fBChapter 9\fP\s-1

\s+1\fBResource Management\fP\s-1
.sp 2
.nr H1 9
.nr H2 0
.nr H3 0
.nr H4 0
.nr H5 0
.LP
.XS
Chapter 9 \- Resource Management
.XE
A resource is a field in the widget record with a corresponding
resource entry in the \fIresources\fP list of the widget or any of its
superclasses.
This means that the field is
settable by
.PN XtCreateWidget
(by naming the field in the argument list), by an
entry in a resource file (by using either the name or class), and by
.PN XtSetValues .
In addition, it is readable by
.PN XtGetValues .
Not all fields in a widget record are resources.
Some are for bookkeeping use by the
generic routines (like \fImanaged\fP and \fIbeing_destroyed\fP).
Others can be for local bookkeeping,
and still others are derived from resources 
(many graphics contexts and pixmaps).
.LP
Widgets typically need to obtain a large set of resources at widget
creation time.
Some of the resources come from the argument list supplied in the call to
.PN XtCreateWidget ,
some from the resource database,
and some from the internal defaults specified by the widget.
Resources are obtained first from the argument list,
then from the resource database for all resources not specified
in the argument list,
and last, from the internal default, if needed.

.NH 2
Resource Lists
.XS
\*(SN Resource Lists
.XE
.LP
.IN "Resource Management"
A resource entry specifies a field in the widget,
the textual name and class of the field that argument lists
and external resource files use to refer to the field,
and a default value that the field should get if no value is specified.
The declaration for the
.PN XtResource
structure is
.LP
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	String resource_name;
	String resource_class;
	String resource_type;
	Cardinal resource_size;
	Cardinal resource_offset;
	String default_type;
	XtPointer default_addr;
} XtResource, *XtResourceList;
.De
.IN "XtResourceList"

.LP
When the resource list is specified as the
.PN CoreClassPart ,
.PN ObjectClassPart ,
.PN RectObjClassPart ,
or
.PN ConstraintClassPart
\fIresources\fP field the strings pointed to by \fIresource_name\fP,
\fIresource_class\fP, \fIresource_type\fP, and \fIdefault_type\fP must
be permanently allocated prior to or during the execution of the class
initialization procedure and must not be subsequently deallocated.

.LP
The \fIresource_name\fP field contains the name used by clients to access the field
in the widget.
By convention, it starts with a lower-case letter
and is spelled exactly like the field name,
except all underscores (_) are deleted and the next letter is replaced by its 
upper-case counterpart.
For example, the resource name for background_pixel becomes backgroundPixel.
Resource names beginning with the two-character
sequence ``xt'' and resource classes beginning with the two-character
sequence ``Xt'' are reserved to the \*(xI for future standard and
implementation-dependent uses.
Widget header files typically contain a symbolic name for each resource name.
All resource names, classes, and types used by the \*(xI are named in
.Pn < X11/StringDefs.h >.
The \*(xI's symbolic resource names begin with
``XtN''
and are followed by the string name (for example, XtNbackgroundPixel
for backgroundPixel).

.LP
The \fIresource_class\fP field contains the class string used in resource
specification files to identify the field.
A resource class provides two functions:
.IP \(bu 5
It isolates an application from different representations that widgets 
can use for a similar resource.
.IP \(bu 5
It lets you specify values for several actual resources with a single name.
A resource class should be chosen to span a group of closely related fields.
.LP
For example,
a widget can have several pixel resources: background, foreground,
border, block cursor, pointer cursor, and so on.
Typically, the background defaults to white
and everything else to black.
The resource class for each of these resources in the resource list
should be chosen so that it takes the minimal number of entries
in the resource database to make the background offwhite
and everything else darkblue.
.LP
In this case, the background pixel should have a resource class of
``Background''
and all the other pixel entries a resource class of
``Foreground''.
Then, the resource file needs only two lines to
change all pixels to offwhite or darkblue:
.LP
.Ds 5
.TA .5i 1.5i
.ta .5i 1.5i
*Background:	offwhite
*Foreground:	darkblue
.De
.LP
Similarly, a widget may have several font resources (such as normal and bold),
but all fonts should have the class Font.
Thus, changing all fonts simply requires only a single line in the 
default resource file:
.LP
.Ds 5
.TA .5i 3i
.ta .5i 3i
*Font:	6x13
.De
.LP
By convention,
resource classes are always spelled starting with a capital letter
to distinguish them from resource names.
Their symbolic names are preceded with
``XtC''
(for example, XtCBackground).
.LP
The \fIresource_type\fP field gives the physical representation type of the resource
and also encodes information about the specific usage of the field.
By convention, it starts with an upper-case letter and is
spelled identically to the type name of the field.
The resource type is used when resources are fetched to
convert from the resource database format (usually
.PN String )
or the format of the resource default value
(almost anything, but often
.PN String )
to the desired
physical representation (see Section 9.6).
The \*(xI define the following resource types:
.TS H
lw(2.75i) lw(2.75i).
_
.sp 6p
Resource Type	Structure or Field Type
.sp 6p
_
.sp 6p
.TH
.R
T{
.PN XtRAcceleratorTable
T}	XtAccelerators
T{
.PN XtRAtom
T}	Atom
T{
.PN XtRBitmap
T}	Pixmap, depth=1
T{
.PN XtRBoolean
T}	Boolean
T{
.PN XtRBool
T}	Bool
T{
.PN XtRCallback
T}	XtCallbackList
T{
.PN XtRCardinal
T}	Cardinal
T{
.PN XtRColor
T}	XColor
T{
.PN XtRColormap
T}	Colormap
T{
.PN XtRCommandArgArray
T}	String*
T{
.PN XtRCursor
T}	Cursor
T{
.PN XtRDimension
T}	Dimension
T{
.PN XtRDirectoryString
T}	String
T{
.PN XtRDisplay
T}	Display*
T{
.PN XtREnum
T}	XtEnum
T{
.PN XtREnvironmentArray
T}	String*
T{
.PN XtRFile
T}	FILE*
T{
.PN XtRFloat
T}	float
T{
.PN XtRFont
T}	Font
T{
.PN XtRFontSet
T}	XFontSet
T{
.PN XtRFontStruct
T}	XFontStruct*
T{
.PN XtRFunction
T}	(*)()
T{
.PN XtRGeometry
T}	T{
char*, format as defined by
.PN XParseGeometry
T}
T{
.PN XtRGravity
T}	int
T{
.PN XtRInitialState
T}	int
T{
.PN XtRInt
T}	int
T{
.PN XtRLongBoolean
T}	long
T{
.PN XtRObject
T}	Object
T{
.PN XtRPixel
T}	Pixel
T{
.PN XtRPixmap
T}	Pixmap
T{
.PN XtRPointer
T}	XtPointer
T{
.PN XtRPosition
T}	Position
T{
.PN XtRRestartStyle
T}	unsigned char
T{
.PN XtRScreen
T}	Screen*
T{
.PN XtRShort
T}	short
T{
.PN XtRSmcConn
T}	XtPointer
T{
.PN XtRString
T}	String
T{
.PN XtRStringArray
T}	String*
T{
.PN XtRStringTable
T}	String*
T{
.PN XtRTranslationTable
T}	XtTranslations
T{
.PN XtRUnsignedChar
T}	unsigned char
T{
.PN XtRVisual
T}	Visual*
T{
.PN XtRWidget
T}	Widget
T{
.PN XtRWidgetClass
T}	WidgetClass
T{
.PN XtRWidgetList
T}	WidgetList
T{
.PN XtRWindow
T}	Window
.sp 6p
_
.TE
.sp
.LP
.Pn < X11/StringDefs.h >
also defines the following resource types as a
convenience for widgets, although they do not have any corresponding
data type assigned:
.PN XtREditMode ,
.PN XtRJustify ,
and
.PN XtROrientation .
.LP
The \fIresource_size\fP field is the size of the physical representation in bytes;
you should specify it as
.PN sizeof (\fItype\fP)
so that the
compiler fills in the value.
The \fIresource_offset\fP field is the offset in bytes of the field 
within the widget.
You should use the
.PN XtOffsetOf
macro to retrieve this value.
The \fIdefault_type\fP field is the representation type of the default
resource value.
If \fIdefault_type\fP is different from \fIresource_type\fP and the default value
is needed,
the resource manager invokes a conversion procedure from \fIdefault_type\fP
to \fIresource_type\fP.
Whenever possible,
the default type should be identical to the resource type in order
to minimize widget creation time.
However, there are sometimes no values of the type that the program 
can easily specify.
In this case,
it should be a value for which the converter is guaranteed to work (for example, 
.PN XtDefaultForeground
for a pixel resource).
The \fIdefault_addr\fP field specifies the address of the default resource value.
As a special case, if \fIdefault_type\fP is
.PN XtRString ,
then the value in the \fIdefault_addr\fP field is the pointer to
the string rather than a pointer to the pointer.
The default is used if a resource is not specified in the argument list
or in the resource database, or if the conversion from the representation
type stored in the resource database fails,
which can happen for various reasons (for example, a misspelled entry in a
resource file).
.LP
Two special representation types 
(XtRImmediate
and
XtRCallProc)
are usable only as default resource types.
XtRImmediate
indicates that the value in the \fIdefault_addr\fP field is the actual value of
the resource rather than the address of the value. 
The value must be in the correct representation type for the resource,
coerced to an
.PN XtPointer .
No conversion is possible, since there is no source representation type.
XtRCallProc
indicates that the value in the \fIdefault_addr\fP field is a procedure
pointer.
This procedure is automatically invoked with the widget,
\fIresource_offset\fP, and a pointer to an
.PN XrmValue
in which to store the result.
XtRCallProc
procedure pointers are of type
.PN XtResourceDefaultProc .
.FD 0
typedef void (*XtResourceDefaultProc)(Widget, int, XrmValue*);
.br
      Widget \fIw\fP;
.br
      int \fIoffset\fP;
.br
      XrmValue *\fIvalue\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget whose resource value is to be obtained.
.IP \fIoffset\fP 1i
Specifies the offset of the field in the widget record.
.IP \fIvalue\fP 1i
Specifies the resource value descriptor to return.
.LP
The
.PN XtResourceDefaultProc
procedure should fill in the \fIvalue->addr\fP field with a pointer 
to the resource value in its correct representation type.
.sp
.LP
To get the resource list structure for a particular class, use
.PN XtGetResourceList .
.IN "XtGetResourceList" "" "@DEF@"
.FD 0
void XtGetResourceList(\fIclass\fP, \fIresources_return\fP, \fInum_resources_return\fP);
.br
      WidgetClass \fIclass\fP;
.br
      XtResourceList *\fIresources_return\fP;
.br
      Cardinal *\fInum_resources_return\fP;
.FN
.IP \fIclass\fP 1.5i
Specifies the object class to be queried.  It must be
.PN objectClass
or any subclass thereof.
.IP \fIresources_return\fP 1.5i
Returns the resource list.
.IP \fInum_resources_return\fP 1.5i
Returns the number of entries in the resource list.
.LP
If
.PN XtGetResourceList
is called before the class is initialized,
it returns the resource list as specified in the class record.
If it is called after the class has been initialized,
.PN XtGetResourceList
returns a merged resource list that includes the resources 
for all superclasses.
The list returned by
.PN XtGetResourceList
should be freed using
.PN XtFree
when it is no longer needed.
.sp
.LP
To get the constraint resource list structure for a particular widget
class, use
.PN XtGetConstraintResourceList .
.IN "XtGetConstraintResourceList" "" "@DEF@"
.FD 0
void XtGetConstraintResourceList(\fIclass\fP, \fIresources_return\fP, \
\fInum_resources_return\fP)
.br
      WidgetClass \fIclass\fP;
.br
      XtResourceList *\fIresources_return\fP;
.br
      Cardinal *\fInum_resources_return\fP;
.FN
.IP \fIclass\fP 1.5i
Specifies the object class to be queried.  It must be
.PN objectClass
or any subclass thereof.
.IP \fIresources_return\fP 1.5i
Returns the constraint resource list.
.IP \fInum_resources_return\fP 1.5i
Returns the number of entries in the constraint resource list.
.LP
If
.PN XtGetConstraintResourceList
is called before the widget class is
initialized, the resource list as specified in the widget
class Constraint part is returned.  If
.PN XtGetConstraintResourceList
is called after the widget class has been initialized, the merged
resource list for the class and all Constraint superclasses is
returned.  If the
specified class is not a subclass of
.PN constraintWidgetClass ,
*\fIresources_return\fP is set to NULL
and *\fInum_resources_return\fP is set to zero.
The list returned by
.PN XtGetConstraintResourceList
should be freed using
.PN XtFree
when it is no longer needed.
.sp
.LP
The routines
.PN XtSetValues
and
.PN XtGetValues
also use the resource list to set and get widget state;
see Sections 9.7.1 and 9.7.2.
.LP
Here is an abbreviated version of a possible resource list for a Label widget:
.LP
.Ds
.TA .5i 1.5i 3i
.ta .5i 1.5i 3i
/* Resources specific to Label */
static XtResource resources[] = {
{XtNforeground, XtCForeground, XtRPixel, sizeof(Pixel),
   XtOffsetOf(LabelRec, label.foreground), XtRString, XtDefaultForeground},
{XtNfont, XtCFont, XtRFontStruct, sizeof(XFontStruct*),
   XtOffsetOf(LabelRec, label.font), XtRString, XtDefaultFont},
{XtNlabel, XtCLabel, XtRString, sizeof(String),
   XtOffsetOf(LabelRec, label.label), XtRString, NULL},
	.
	.
	.
}
.De
.LP
The complete resource name for a field of a widget instance is the
concatenation of the application shell name (from 
.PN XtAppCreateShell ),
the instance names of all the widget's parents up to the 
top of the widget tree,
the instance name of the widget itself,
and the resource name of the specified field of the widget.
Similarly,
the full resource class of a field of a widget instance is the
concatenation of the application class (from
.PN XtAppCreateShell ),
the widget class names of all the widget's parents up to the 
top of the widget tree,
the widget class name of the widget itself,
and the resource class of the specified field of the widget.

.NH 2
Byte Offset Calculations
.XS
\*(SN Byte Offset Calculations
.XE
.LP
To determine the byte offset of a field within a structure type, use
.PN XtOffsetOf .
.IN "XtOffsetOf" "" "@DEF@"
.FD 0
Cardinal XtOffsetOf(\fIstructure_type\fP, \fIfield_name\fP)
.br
      \fIType structure_type\fP;
.br
      \fIField field_name\fP;
.FN
.IP \fIstructure_type\fP 1i
Specifies a type that is declared as a structure.
.IP \fIfield_name\fP 1i
Specifies the name of a member within the structure.
.LP
The
.PN XtOffsetOf
macro expands to a constant expression that gives the
offset in bytes to the specified structure member from the beginning
of the structure.  It is normally used to statically initialize
resource lists and is more portable than
.PN XtOffset ,
which serves the same function.

.LP
To determine the byte offset of a field within a structure pointer type, use
.PN XtOffset .
.IN "XtOffset" "" "@DEF@"
.FD 0
Cardinal XtOffset(\fIpointer_type\fP, \fIfield_name\fP)
.br
      \fIType pointer_type\fP;
.br
      \fIField field_name\fP;
.FN
.IP \fIpointer_type\fP 1i
Specifies a type that is declared as a pointer to a structure.
.IP \fIfield_name\fP 1i
Specifies the name of a member within the structure.
.LP
The
.PN XtOffset
macro expands to a constant expression that gives the
offset in bytes to the specified structure member from the beginning
of the structure.  It may be used to statically initialize
resource lists.
.PN XtOffset
is less portable than
.PN XtOffsetOf .

.NH 2
Superclass-to-Subclass Chaining of Resource Lists
.XS
\*(SN Superclass-to-Subclass Chaining of Resource Lists
.XE
.LP
.IN "Inheritance"
.IN "Superclass Chaining"
.IN "Chaining"
The 
.PN XtCreateWidget
function gets resources as a superclass-to-subclass chained operation.
That is, the resources specified in the
.PN objectClass
resource list are fetched,
then those in
.PN rectObjClass ,
and so on down to the resources specified
for this widget's class. Within a class, resources are fetched in the order
they are declared.
.LP
In general, if a widget resource field is declared in a superclass,
that field is included in the superclass's resource list and need not be
included in the subclass's resource list.
For example, the
Core 
class contains a resource entry for \fIbackground_pixel\fP.
Consequently,
the implementation of Label need not also have a resource entry
for \fIbackground_pixel\fP.
However, a subclass,
by specifying a resource entry for that field in its own resource list,
can override the resource entry for any field declared in a superclass.
This is most often done to override the defaults provided in the
superclass with new ones.
At class initialization time, 
resource lists for that class are scanned from the superclass down 
to the class to look for resources with the same offset.
A matching resource in a subclass will be reordered to override
the superclass entry.
If reordering is necessary, a copy of the superclass resource list is made to
avoid affecting other subclasses of the superclass.
.LP
.IN "class_initialize procedure"
.IN "Widget" "class initialization"
Also at class initialization time, the \*(xI produce an
internal representation of the resource list to optimize access time
when creating widgets.  In order to save memory, the \*(xI may
overwrite the storage allocated for the resource list in the class
record; therefore, widgets must allocate resource lists in writable
storage and must not access the list contents directly after the
class_initialize procedure has returned.

.NH 2
Subresources
.XS
\*(SN Subresources
.XE
.LP
A widget does not do anything to retrieve its own resources;
instead,
.PN XtCreateWidget
does this automatically before calling the class initialize procedure.
.LP
Some widgets have subparts that are not widgets but for which the widget
would like to fetch resources.
Such widgets call
.PN XtGetSubresources
to accomplish this.
.IN "XtGetSubresources" "" "@DEF@"
.FD 0
void XtGetSubresources(\fIw\fP, \fIbase\fP, \fIname\fP, \fIclass\fP, \
\fIresources\fP, \fInum_resources\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIw\fP;
.br
      XtPointer \fIbase\fP;
.br
      String \fIname\fP;
.br
      String \fIclass\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the object used to qualify the subpart resource name and
class.  \*(oI
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure into which the
resources will be written.
.IP \fIname\fP 1i
Specifies the name of the subpart.
.IP \fIclass\fP 1i
Specifies the class of the subpart.
.IP \fIresources\fP 1i
Specifies the resource list for the subpart.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP \fIargs\fP 1i
Specifies the argument list to override any other resource specifications.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtGetSubresources
function constructs a name and class list from the application name and class,
the names and classes of all the object's ancestors, and the object itself.
Then it appends to this list the \fIname\fP and \fIclass\fP pair passed in.
The resources are fetched from the argument list, the resource database,
or the default values in the resource list.
Then they are copied into the subpart record.
If \fIargs\fP is NULL,
\fInum_args\fP must be zero.
However, if \fInum_args\fP is zero,
the argument list is not referenced.
.LP
.PN XtGetSubresources
may overwrite the specified resource list with an
equivalent representation in an internal format, which optimizes access
time if the list is used repeatedly.  The resource list must be
allocated in writable storage, and the caller must not modify the list
contents after the call if the same list is to be used again.
Resources fetched by
.PN XtGetSubresources
are reference-counted as
if they were referenced by the specified object.  Subresources might
therefore be freed from the conversion cache and destroyed
when the object is destroyed, but not before then.
.sp
.LP
To fetch resources for widget subparts using varargs lists, use
.PN XtVaGetSubresources .
.IN "XtVaGetSubresources" "" "@DEF@"
.FD 0
void XtVaGetSubresources(\fIw\fP, \fIbase\fP, \fIname\fP, \fIclass\fP, \
\fIresources\fP, \fInum_resources\fP, ...)
.br
    Widget \fIw\fP;
.br
    XtPointer \fIbase\fP;
.br
    String \fIname\fP;
.br
    String \fIclass\fP;
.br
    XtResourceList \fIresources\fP;
.br
    Cardinal \fInum_resources\fP;
.FN
.IP \fIw\fP 1i
Specifies the object used to qualify the subpart resource name and
class.  \*(oI
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure into which the
resources will be written.
.IP \fIname\fP 1i
Specifies the name of the subpart.
.IP \fIclass\fP 1i
Specifies the class of the subpart.
.IP \fIresources\fP 1i
Specifies the resource list for the subpart.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP ... 1i
Specifies the variable argument list to override any other
resource specifications.
.LP
.PN XtVaGetSubresources
is identical in function to
.PN XtGetSubresources
with the \fIargs\fP and \fInum_args\fP parameters replaced by a varargs list, as
described in Section 2.5.1.

.NH 2
Obtaining Application Resources
.XS
\fB\*(SN Obtaining Application Resources\fP
.XE
.LP
To retrieve resources that are not specific to a widget
but apply to the overall application, use
.PN XtGetApplicationResources .
.IN "XtGetApplicationResources" "" "@DEF@"
.FD 0
void XtGetApplicationResources(\fIw\fP, \fIbase\fP, \fIresources\fP, \
\fInum_resources\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIw\fP;
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the object that identifies the resource database to search
(the database is that associated with the display for this object).  \*(oI
.IP \fIbase\fP 1i
Specifies the base address into which
the resource values will be written.
.IP \fIresources\fP 1i
Specifies the resource list.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP \fIargs\fP 1i
Specifies the argument list to override any other resource specifications.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtGetApplicationResources
function first uses the passed object,
which is usually an application shell widget,
to construct a resource name and class list.
The full name and class of the specified object (that is, including its
ancestors, if any) is logically added to the
front of each resource name and class.
Then it retrieves the resources from the argument list,
the resource database, or the resource list default values.
After adding base to each address,
.PN XtGetApplicationResources
copies the resources into the addresses
obtained by adding \fIbase\fP to each \fIoffset\fP in the resource list.
If \fIargs\fP is NULL,
\fInum_args\fP must be zero.
However, if \fInum_args\fP is zero,
the argument list is not referenced.
The portable way to specify application resources is to declare them
as members of a structure and pass the address of the structure 
as the \fIbase\fP argument.
.LP
.PN XtGetApplicationResources
may overwrite the specified resource list
with an equivalent representation in an internal format, which
optimizes access time if the list is used repeatedly.  The resource
list must be allocated in writable storage, and the caller must not
modify the list contents after the call if the same list is to be
used again.  Any per-display resources fetched by
.PN XtGetApplicationResources
will not be freed from the resource cache until the display is closed.
.sp
.LP
To retrieve resources for the overall application using varargs lists, use
.PN XtVaGetApplicationResources .
.IN "XtVaGetApplicationResources" "" "@DEF@"
.FD 0
void XtVaGetApplicationResources(\fIw\fP, \fIbase\fP, \fIresources\fP, \
\fInum_resources\fP, ...)
.br
      Widget \fIw\fP;
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.FN
.IP \fIw\fP 1i
Specifies the object that identifies the resource database to search
(the database is that associated with the display for this object).  \*(oI
.IP \fIbase\fP 1i
Specifies the base address into which
the resource values will be written.
.IP \fIresources\fP 1i
Specifies the resource list for the subpart.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP ... 1i
Specifies the variable argument list to override any other
resource specifications.
.LP
.PN XtVaGetApplicationResources
is identical in function to
.PN XtGetApplicationResources
with the \fIargs\fP and \fInum_args\fP parameters
replaced by a varargs list, as described in Section 2.5.1.

.NH 2
Resource Conversions
.XS
\*(SN Resource Conversions
.XE
.LP
The \*(xI provide a mechanism for registering representation converters that
are automatically invoked by the resource-fetching routines.
The \*(xI additionally provide and register several commonly used converters.
This resource conversion mechanism serves several purposes:
.IP \(bu 5
It permits user and application resource files to contain textual
representations of nontextual values.
.IP \(bu 5
It allows textual or other representations of default resource values that
are dependent on the display, screen, or colormap, and thus must be
computed at runtime.
.IP \(bu 5
It caches conversion source and result data.
Conversions that require much computation or space
(for example, string-to-translation-table)
or that require round-trips to the server
(for example, string-to-font or string-to-color) are performed only once.

.NH 3
Predefined Resource Converters
.XS
\*(SN Predefined Resource Converters
.XE
.LP
The \*(xI define all the representations used in the 
Object,
RectObj,
Core, 
Composite, 
Constraint, 
and 
Shell 
widget classes.
The \*(xI register the following resource converters that accept
input values of representation type
.PN XtRString .
.LP
.TS
lw(1.7i) lw(2.25i) lw(1.5i) .
_
.sp 6p
Target Representation	Converter Name	Additional Args
.sp 6p
_
.sp 6p
T{
.PN XtRAcceleratorTable
T}	T{
.PN XtCvtStringToAcceleratorTable
T}
T{
.PN XtRAtom
T}	T{
.PN XtCvtStringToAtom
T}	Display*
T{
.PN XtRBoolean
T}	T{
.PN XtCvtStringToBoolean
T}
T{
.PN XtRBool
T}	T{
.PN XtCvtStringToBool
T}
T{
.PN XtRCommandArgArray
T}	T{
.PN XtCvtStringToCommandArgArray
T}
T{
.PN XtRCursor
T}	T{
.PN XtCvtStringToCursor
T}	Display*
T{
.PN XtRDimension
T}	T{
.PN XtCvtStringToDimension
T}
T{
.PN XtRDirectoryString
T}	T{
.PN XtCvtStringToDirectoryString
T}
T{
.PN XtRDisplay
T}	T{
.PN XtCvtStringToDisplay
T}
T{
.PN XtRFile
T}	T{
.PN XtCvtStringToFile
T}
T{
.PN XtRFloat
T}	T{
.PN XtCvtStringToFloat
T}
T{
.PN XtRFont
T}	T{
.PN XtCvtStringToFont
T}	Display*
T{
.PN XtRFontSet
T}	T{
.PN XtCvtStringToFontSet
T}	Display*, String \fIlocale\fP
T{
.PN XtRFontStruct
T}	T{
.PN XtCvtStringToFontStruct
T}	Display*
T{
.PN XtRGravity
T}	T{
.PN XtCvtStringToGravity
T}
T{
.PN XtRInitialState
T}	T{
.PN XtCvtStringToInitialState
T}
T{
.PN XtRInt
T}	T{
.PN XtCvtStringToInt
T}
T{
.PN XtRPixel
T}	T{
.PN XtCvtStringToPixel
T}	T{
.PN colorConvertArgs
T}
T{
.PN XtRPosition
T}	T{
.PN XtCvtStringToPosition
T}
T{
.PN XtRRestartStyle
T}	T{
.PN XtCvtStringToRestartStyle
T}
T{
.PN XtRShort
T}	T{
.PN XtCvtStringToShort
T}
T{
.PN XtRTranslationTable
T}	T{
.PN XtCvtStringToTranslationTable
T}
T{
.PN XtRUnsignedChar
T}	T{
.PN XtCvtStringToUnsignedChar
T}
T{
.PN XtRVisual
T}	T{
.PN XtCvtStringToVisual
T}	Screen*, Cardinal \fIdepth\fP
.sp 6p
_
.TE

.LP
The String-to-Pixel conversion has two predefined constants that are
guaranteed to work and contrast with each other:
.PN XtDefaultForeground
and
.PN XtDefaultBackground .
.IN "XtDefaultBackground" "" "@DEF@"
.IN "XtDefaultForeground" "" "@DEF@"
They evaluate to the black and white pixel values of the widget's screen, 
respectively.
.IN "Resources" "reverseVideo"
If the application resource reverseVideo is
.PN True ,
they evaluate to the white and black pixel values of the widget's screen,
respectively.
Similarly, the String-to-Font and String-to-FontStruct converters recognize
the constant
.PN XtDefaultFont
.IN "XtDefaultFont" "" "@DEF@"
.IN "Resources" "xtDefaultFont"
and evaluate this in the following manner:
.IP \(bu 5
Query the resource database for the resource whose full name
is ``xtDefaultFont'', class ``XtDefaultFont'' (that is, no widget
name/class prefixes) and use a type
.PN XtRString
value returned as the font name, or a type
.PN XtRFont
or
.PN XtRFontStruct
value directly as the resource value.
.IP \(bu 5
If the resource database does not contain a value for xtDefaultFont,
class XtDefaultFont, or if the returned font name cannot be
successfully opened, an implementation-defined font in ISO8859-1
character set encoding is opened.  (One possible algorithm is to
perform an
.PN XListFonts
using a wildcard font name and use the first
font in the list.  This wildcard font name should be as broad as
possible to maximize the probability of locating a useable font;
for example, "-*-*-*-R-*-*-*-120-*-*-*-*-ISO8859-1".)
.IP \(bu 5
If no suitable ISO8859-1 font can be found, issue a warning message
and return
.PN False .
.LP
The String-to-FontSet converter recognizes the constant
.PN XtDefaultFontSet
.IN "XtDefaultFontSet" "" "@DEF@"
.IN "Resources" "xtDefaultFontSet"
and evaluate this in the following manner:
.IP \(bu 5
Query the resource database for the resource whose full name
is ``xtDefaultFontSet'', class ``XtDefaultFontSet'' (that is, no widget
name/class prefixes) and use a type
.PN XtRString
value returned as the base font name list, or a type
.PN XtRFontSet
value directly as the resource value.
.IP \(bu 5
If the resource database does not contain a value for xtDefaultFontSet,
class XtDefaultFontSet, or if a font set cannot be
successfully created from this resource,
an implementation-defined font set is created.
(One possible algorithm is to
perform an
.PN XCreateFontSet
using a wildcard base font name.
This wildcard base font name should be as broad as
possible to maximize the probability of locating a useable font;
for example, "-*-*-*-R-*-*-*-120-*-*-*-*".)
.IP \(bu 5
If no suitable font set can be created, issue a warning message
and return
.PN False .
.LP
If a font set is created but \fImissing_charset_list\fP is not
empty, a warning is issued and the partial font set is returned.
The \*(xI register the String-to-FontSet converter with
a conversion argument list that extracts the current process
locale at the time the converter is invoked.   This ensures
that the converter is invoked again if the same conversion
is required in a different locale.
.LP
The String-to-Gravity conversion accepts string values which are the
names of window and bit gravities and their numerical equivalents,
as defined in \fI\*(xL\fP:
.PN ForgetGravity ,
.PN UnmapGravity ,
.PN NorthWestGravity ,
.PN NorthGravity ,
.PN NorthEastGravity ,
.PN WestGravity ,
.PN CenterGravity ,
.PN EastGravity ,
.PN SouthWestGravity ,
.PN SouthGravity , 
.PN SouthEastGravity , 
and
.PN StaticGravity .
Alphabetic case is not significant in the conversion.
.LP
The String-to-CommandArgArray conversion parses a String into an
array of strings.
White space characters separate elements of the command line.
The converter recognizes the backslash character `\\' as an escape
character to allow the following white space character to be part of the
array element.
.LP
.IN "XtCurrentDirectory" "" "@DEF@"
The String-to-DirectoryString conversion recognizes the
string "XtCurrentDirectory" and returns the result of a call
to the operating system to get the current directory.
.LP
The String-to-RestartStyle conversion accepts the values 
.PN RestartIfRunning ,
.PN RestartAnyway ,
.PN RestartImmediately ,
and
.PN RestartNever
as defined by the \fIX Session Management Protocol\fP.
.LP
The String-to-InitialState conversion accepts the values
.PN NormalState
or
.PN IconicState
as defined by the \fI\*(xC\fP.
.LP
The String-to-Visual conversion calls
.PN XMatchVisualInfo
using the
\fIscreen\fP and \fIdepth\fP fields from the core part and returns the first
matching Visual on the list.  The widget resource list must be certain
to specify any resource of type
.PN XtRVisual
after the depth resource.
The allowed string values are the visual class names defined in \fI\*(xP\fP,
Section 8;
.PN StaticGray ,
.PN StaticColor ,
.PN TrueColor ,
.PN GrayScale ,
.PN PseudoColor ,
and
.PN DirectColor .

.LP
The \*(xI register the following resource converter that accepts
an input value of representation type
.PN XtRColor .
.LP
.TS
lw(1.5i) lw(2.25i) lw(1.5i) .
_
.sp 6p
Target Representation	Converter Name	Additional Args
.sp 6p
_
.sp 6p
T{
.PN XtRPixel
T}	T{
.PN XtCvtColorToPixel
T}
.sp 6p
_
.TE

.LP
The \*(xI register the following resource converters that accept
input values of representation type
.PN XtRInt .
.LP
.TS
lw(1.5i) lw(2.25i) lw(1.5i) .
_
.sp 6p
Target Representation	Converter Name	Additional Args
.sp 6p
_
.sp 6p
T{
.PN XtRBoolean
T}	T{
.PN XtCvtIntToBoolean
T}
T{
.PN XtRBool
T}	T{
.PN XtCvtIntToBool
T}
T{
.PN XtRColor
T}	T{
.PN XtCvtIntToColor
T}	T{
.PN colorConvertArgs
T}
T{
.PN XtRDimension
T}	T{
.PN XtCvtIntToDimension
T}
T{
.PN XtRFloat
T}	T{
.PN XtCvtIntToFloat
T}
T{
.PN XtRFont
T}	T{
.PN XtCvtIntToFont
T}
T{
.PN XtRPixel
T}	T{
.PN XtCvtIntToPixel
T}
T{
.PN XtRPixmap
T}	T{
.PN XtCvtIntToPixmap
T}
T{
.PN XtRPosition
T}	T{
.PN XtCvtIntToPosition
T}
T{
.PN XtRShort
T}	T{
.PN XtCvtIntToShort
T}
T{
.PN XtRUnsignedChar
T}	T{
.PN XtCvtIntToUnsignedChar
T}
.sp 6p
_
.TE

.LP
The \*(xI register the following resource converter that accepts
an input value of representation type
.PN XtRPixel .
.LP
.TS
lw(1.5i) lw(2.25i) lw(1.5i) .
_
.sp 6p
Target Representation	Converter Name	Additional Args
.sp 6p
_
.sp 6p
T{
.PN XtRColor
T}	T{
.PN XtCvtPixelToColor
T}
.sp 6p
_
.TE

.NH 3
New Resource Converters
.XS
\*(SN New Resource Converters
.XE
.LP
Type converters use pointers to
.PN XrmValue
structures (defined in
.Pn < X11/Xresource.h >;
see Section 15.4 in \fI\*(xL\fP)
for input and output values.
.LP
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	unsigned int size;
	XPointer addr;
} XrmValue, *XrmValuePtr;
.De
.LP
The \fIaddr\fP field specifies the address of the data and the \fIsize\fP field
gives the total number of significant bytes in the data.  For values
of type
.PN String ,
\fIaddr\fP is the address of the first character and \fIsize\fP
includes the NUL terminating byte. 
.LP
A resource converter procedure pointer is of type
.PN XtTypeConverter .
.IN "XtTypeConverter" "" "@DEF@"
.FD 0
typedef Boolean (*XtTypeConverter)(Display*, XrmValue*, Cardinal*,
                              XrmValue*, XrmValue*, XtPointer*);
.br
      Display *\fIdisplay\fP;
.br
      XrmValue *\fIargs\fP;
.br
      Cardinal *\fInum_args\fP;
.br
      XrmValue *\fIfrom\fP;
.br
      XrmValue *\fIto\fP;
.br
      XtPointer *\fIconverter_data\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the display connection with which this conversion is associated.
.IP \fIargs\fP 1i
Specifies a list of additional
.PN XrmValue
arguments to the converter if additional context is needed
to perform the conversion, or NULL.
For example, the String-to-Font converter needs the widget's \fIdisplay\fP,
and the String-to-Pixel converter needs the widget's \fIscreen\fP and \fIcolormap\fP.
.IP \fInum_args\fP 1i
Specifies the number of entries in \fIargs\fP.
.IP \fIfrom\fP 1i
Specifies the value to convert.
.IP \fIto\fP 1i
Specifies a descriptor for a location into which to store the converted value.
.IP \fIconverter_data\fP 1i
Specifies a location into which the converter may
store converter-specific data associated
with this conversion.
.LP
The \fIdisplay\fP argument is normally used only when generating error
messages, to identify the application context (with the function
.PN XtDisplayToApplicationContext ).
.LP
The \fIto\fP argument specifies the size and location into which the
converter should store the converted value.  If the \fIaddr\fP field is NULL,
the converter should allocate appropriate storage and store the size
and location into the \fIto\fP descriptor.  If the type converter allocates
the storage, it remains under the ownership of the converter and must
not be modified by the caller.  The type converter is permitted to use
static storage for this purpose, and therefore the caller must
immediately copy the data upon return from the converter.  If the
\fIaddr\fP field is not NULL, the converter must check the \fIsize\fP field to
ensure that sufficient space has been allocated before storing the
converted value.  If insufficient space is specified, the converter
should update the \fIsize\fP field with the number of bytes required and
return
.PN False
without modifying the data at the specified location.
If sufficient space was allocated by the caller, the converter should
update the \fIsize\fP field with the number of bytes actually occupied by the
converted value.  For converted values of type
.PN XtRString ,
the size should
include the NULL terminating byte, if any.
The converter may store any value in the location specified
in \fIconverter_data\fP; this data will be passed to the destructor, if any,
when the resource is freed by the \*(xI.
.LP
The converter must return
.PN True
if the conversion was successful and
.PN False
otherwise.  If the conversion cannot be performed because of an
improper source value, a warning message should also be issued with
.PN XtAppWarningMsg .

.LP
Most type converters just take the data described by the specified \fIfrom\fP
argument and return data by writing into the location specified in
the \fIto\fP argument.
A few need other information, which is available in \fIargs\fP.
A type converter can invoke another type converter,
which allows differing sources that may convert into a common intermediate
result to make maximum use of the type converter cache.
.LP
Note that if an address is written into \fIto->addr\fP, it cannot be that
of a local variable of the converter because the data will not be
valid after the converter returns.  Static variables may be used,
as in the following example.
If the converter modifies the resource database,
the changes affect any in-progress widget creation,
.PN XtGetApplicationResources ,
or
.PN XtGetSubresources
in an implementation-defined manner; however, insertion of new entries
or changes to existing entries is allowed and will not directly cause
an error.

.LP
The following is an example of a converter that takes a
.PN string
and converts it to a
.PN Pixel .
Note that the \fIdisplay\fP parameter is only
used to generate error messages; the
.PN Screen
conversion argument is
still required to inform the \*(xI that the converted value is
a function of the particular display (and colormap).
.LP
.Ds 0
.TA .3i .7i 1i 1.3i 1.7i 2i 4i
.ta .3i .7i 1i 1.3i 1.7i 2i 4i

#define done(type, value) \\
	{						\\
		if (toVal->addr != NULL) {		\\
			if (toVal->size < sizeof(type)) {	\\
				toVal->size = sizeof(type);	\\
				return False;	\\
			}				\\
			*(type*)(toVal->addr) = (value);	\\
		}					\\
		else {				\\
			static type static_val;	\\
			static_val = (value);	\\
			toVal->addr = (XPointer)&static_val;	\\
		}					\\
		toVal->size = sizeof(type);	\\
		return True;			\\
	}

static Boolean CvtStringToPixel(dpy, args, num_args, fromVal, toVal, converter_data)
	Display	*dpy;
	XrmValue	*args;
	Cardinal	*num_args;
	XrmValue	*fromVal;
	XrmValue	*toVal;
	XtPointer	*converter_data;
{
	static XColor	screenColor;
	XColor		exactColor;
	Screen		*screen;
	Colormap		colormap;
	Status			status;

	if (*num_args != 2)
		XtAppWarningMsg(XtDisplayToApplicationContext(dpy),
			"wrongParameters", "cvtStringToPixel", "XtToolkitError",
			"String to pixel conversion needs screen and colormap arguments",
			(String *)NULL, (Cardinal *)NULL);

	screen = *((Screen**) args[0].addr);
	colormap = *((Colormap *) args[1].addr);

	if (CompareISOLatin1(str, XtDefaultBackground) == 0) {
		*closure_ret = False;
		done(Pixel, WhitePixelOfScreen(screen));
	}
	if (CompareISOLatin1(str, XtDefaultForeground) == 0) {
		*closure_ret = False;
		done(Pixel, BlackPixelOfScreen(screen));
	}


	status = XAllocNamedColor(DisplayOfScreen(screen), colormap, (char*)fromVal->addr, 
				               &screenColor, &exactColor);

	if (status == 0) {
		String params[1];
		Cardinal num_params = 1;
		params[0] = (String)fromVal->addr;
		XtAppWarningMsg(XtDisplayToApplicationContext(dpy),
			"noColormap", "cvtStringToPixel", "XtToolkitError",
			"Cannot allocate colormap entry for \\"%s\\"", params,\
 &num_params);
	        *converter_data = (char *) False;
                return False;
	} else {
                *converter_data = (char *) True;
		done(Pixel, &screenColor.pixel);
	}
}
.De
.LP
All type converters should define some set of conversion values for which they
are guaranteed to succeed so these can be used in the resource defaults.
This issue arises only with conversions, such as fonts and colors,
where there is no string representation that all server implementations
will necessarily recognize.
For resources like these,
the converter should define a symbolic constant
in the same manner as
.PN XtDefaultForeground ,
.PN XtDefaultBackground ,
and
.PN XtDefaultFont .
.sp
.LP
To allow the \*(xI to deallocate resources produced by type
converters, a resource destructor procedure may also be provided.
.LP
A resource destructor procedure pointer is of type
.PN XtDestructor .
.IN "XtDestructor" "" "@DEF@"
.FD 0
typedef void (*XtDestructor) (XtAppContext, XrmValue*, XtPointer, XrmValue*, \
Cardinal*);
.br
      XtAppContext \fIapp\fP;
.br
      XrmValue *\fIto\fP;
.br
      XtPointer \fIconverter_data\fP;
.br
      XrmValue *\fIargs\fP;
.br
      Cardinal *\fInum_args\fP;
.FN
.IP \fIapp\fP 1i
Specifies an application context in which the resource is being freed.
.IP \fIto\fP 1i
Specifies a descriptor for the resource produced by the type converter.
.IP \fIconverter_data\fP 1i
Specifies the converter-specific data returned by the type converter.
.IP \fIargs\fP 1i
Specifies the additional converter arguments as passed
to the type converter when the conversion was performed.
.IP \fInum_args\fP 1i
Specifies the number of entries in \fIargs\fP.
.LP
The destructor procedure is responsible for freeing the resource
specified by the \fIto\fP argument, including any auxiliary storage
associated with that resource, but not the memory directly addressed
by the size and location in the \fIto\fP argument nor the memory specified
by \fIargs\fP.

.NH 3
Issuing Conversion Warnings
.XS
\*(SN Issuing Conversion Warnings
.XE
.LP
The
.PN XtDisplayStringConversionWarning
procedure is a convenience routine for resource type converters
that convert from string values.
.IN "XtDisplayStringConversionWarning" "" "@DEF@"
.FD 0
void XtDisplayStringConversionWarning(\fIdisplay\fP, \fIfrom_value\fP, \
\fIto_type\fP)
.br
      Display *\fIdisplay\fP;
.br
      String \fIfrom_value\fP, \fIto_type\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the display connection with which the conversion is associated.
.IP \fIfrom_value\fP 1i
Specifies the string that could not be converted.
.IP \fIto_type\fP 1i
Specifies the target representation type requested.
.LP
The
.PN XtDisplayStringConversionWarning
procedure issues a warning message using
.PN XtAppWarningMsg
with \fIname\fP ``conversionError'',
\fItype\fP ``string'', \fIclass\fP ``XtToolkitError'', and the default message
``Cannot convert "\fIfrom_value\fP" to type \fIto_type\fP''.
.LP
To issue other types of warning or error messages, the type converter
should use
.PN XtAppWarningMsg
or
.PN XtAppErrorMsg .
.sp
.LP
To retrieve the application context associated with a given
display connection, use
.PN XtDisplayToApplicationContext .
.IN "XtDisplayToApplicationContext" "" "@DEF@"
.FD 0
XtAppContext XtDisplayToApplicationContext( \fIdisplay\fP )
.br
      Display *\fIdisplay\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies an open and initialized display connection.
.LP
The
.PN XtDisplayToApplicationContext
function returns the application
context in which the specified \fIdisplay\fP was initialized.  If the
display is not known to the \*(xI, an error message is issued.

.NH 3
Registering a New Resource Converter
.XS
\fB\*(SN Registering a New Resource Converter\fP
.XE
.LP
When registering a resource converter, the client must specify the
manner in which the conversion cache is to be used when there are multiple
calls to the converter.  Conversion cache control is specified
via an
.PN XtCacheType
.IN "XtCacheType" "" "@DEF@"
argument.
.sp
.Ds 0
typedef int XtCacheType;
.De
.LP
An
.PN XtCacheType
field may contain one of the following values:
.br
.sp
.LP
.PN XtCacheNone
.IN "XtCacheNone" "" "@DEF@"
.IP
Specifies that the results of a previous conversion
may not be reused to satisfy any other resource
requests; the specified converter will be called
each time the converted value is required.
.br
.sp
.LP
.PN XtCacheAll
.IN "XtCacheAll" "" "@DEF@"
.IP
Specifies that the results of a previous conversion
should be reused for any resource request that depends
upon the same source value and conversion arguments.
.br
.sp
.LP
.PN XtCacheByDisplay
.IN "XtCacheByDisplay" "" "@DEF@"
.IP  
Specifies that the results of a previous conversion
should be used as for
.PN XtCacheAll
but the destructor will be called, if specified, if
.PN XtCloseDisplay
is called
for the display connection associated with the converted value, and
the value will be removed from the conversion cache.
.LP
The qualifier
.PN XtCacheRefCount
.IN "XtCacheRefCount" "" "@DEF@"
may be ORed with any of the above values.  If
.PN XtCacheRefCount
is specified, calls to
.PN XtCreateWidget ,
.PN XtCreateManagedWidget ,
.PN XtGetApplicationResources
and
.PN XtGetSubresources
that use the converted value will be counted.  When a widget using the
converted value is destroyed, the count is decremented, and if the
count reaches zero, the destructor procedure will be called and the
converted value will be removed from the conversion cache.

.LP
To register a type converter for all application contexts in a
process, use 
.PN XtSetTypeConverter
and to register a type converter in a single application context, use
.PN XtAppSetTypeConverter .
.IN "XtSetTypeConverter" "" "@DEF@"
.FD 0
void XtSetTypeConverter(\fIfrom_type\fP, \fIto_type\fP, \fIconverter\fP, \
\fIconvert_args\fP, \fInum_args\fP,
                        \fIcache_type\fP, \fIdestructor\fP)
.br
      String \fIfrom_type\fP;
.br
      String \fIto_type\fP;
.br
      XtTypeConverter \fIconverter\fP;
.br
      XtConvertArgList \fIconvert_args\fP;
.br
      Cardinal \fInum_args\fP;
.br
      XtCacheType \fIcache_type\fP;
.br
      XtDestructor \fIdestructor\fP;
.FN
.IP \fIfrom_type\fP 1i
Specifies the source type.
.IP \fIto_type\fP 1i
Specifies the destination type.
.IP \fIconverter\fP 1i
Specifies the resource type converter procedure.
.IP \fIconvert_args\fP 1i
Specifies additional conversion arguments, or NULL.
.IP \fInum_args\fP 1i
Specifies the number of entries in \fIconvert_args\fP.
.IP \fIcache_type\fP 1i
Specifies whether or not resources produced by this
converter are sharable or display-specific and when
they should be freed.
.IP \fIdestructor\fP 1i
Specifies a destroy procedure for resources produced by
this conversion, or NULL if no additional action is
required to deallocate resources produced by the converter.

.sp
.LP
.IN "XtAppSetTypeConverter" "" "@DEF@"
.FD 0
void XtAppSetTypeConverter(\fIapp_context\fP, \fIfrom_type\fP, \fIto_type\fP, \
\fIconverter\fP, \fIconvert_args\fP,
                           \fInum_args\fP, \fIcache_type\fP, \fIdestructor\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fIfrom_type\fP;
.br
      String \fIto_type\fP;
.br
      XtTypeConverter \fIconverter\fP;
.br
      XtConvertArgList \fIconvert_args\fP;
.br
      Cardinal \fInum_args\fP;
.br
      XtCacheType \fIcache_type\fP;
.br
      XtDestructor \fIdestructor\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIfrom_type\fP 1i
Specifies the source type.
.IP \fIto_type\fP 1i
Specifies the destination type.
.IP \fIconverter\fP 1i
Specifies the resource type converter procedure.
.IP \fIconvert_args\fP 1i
Specifies additional conversion arguments, or NULL.
.IP \fInum_args\fP 1i
Specifies the number of entries in \fIconvert_args\fP.
.IP \fIcache_type\fP 1i
Specifies whether or not resources produced by this
converter are sharable or display-specific and when
they should be freed.
.IP \fIdestructor\fP 1i
Specifies a destroy procedure for resources produced by
this conversion, or NULL if no additional action is
required to deallocate resources produced by the converter.
.LP
.PN XtSetTypeConverter
registers the specified type converter and
destructor in all application contexts created by the calling process,
including any future application contexts that may be created.
.PN XtAppSetTypeConverter
registers the specified type converter in the
single application context specified.  If the same \fIfrom_type\fP and
\fIto_type\fP are specified in multiple calls to either function, the most
recent overrides the previous ones.
.sp
.LP
For the few type converters that need additional arguments,
the \*(xI conversion mechanism provides a method of specifying
how these arguments should be computed.
The enumerated type
.PN XtAddressMode
and the structure
.PN XtConvertArgRec
specify how each argument is derived.
These are defined in
.Pn < X11/Intrinsic.h >.
.LP
.Ds 0
.TA .5i 2.5i
.ta .5i 2.5i
typedef enum {
	/* address mode	parameter representation */
	   XtAddress,	/* address */
	   XtBaseOffset,	/* offset */
	   XtImmediate,	/* constant */
	   XtResourceString,	/* resource name string */
	   XtResourceQuark,	/* resource name quark */
	   XtWidgetBaseOffset,	/* offset */
	   XtProcedureArg	/* procedure to call */
} XtAddressMode;

typedef struct {
	XtAddressMode address_mode;
	XtPointer address_id;
	Cardinal size;
} XtConvertArgRec, *XtConvertArgList;
.De
.LP
The \fIsize\fP field specifies the length of the data in bytes.
The \fIaddress_mode\fP field specifies how the \fIaddress_id\fP field should be
interpreted.
.PN XtAddress
.IN "XtAddress" "" "@DEF@"
causes \fIaddress_id\fP to be interpreted as the address of the data.
.PN XtBaseOffset
.IN "XtBaseOffset" "" "@DEF@"
causes \fIaddress_id\fP to be interpreted as the offset from the widget base.
.PN XtImmediate
.IN "XtImmediate" "" "@DEF@"
causes \fIaddress_id\fP to be interpreted as a constant.
.PN XtResourceString
.IN "XtResourceString" "" "@DEF@"
causes \fIaddress_id\fP to be interpreted as the name of a resource
that is to be converted into an offset from the widget base.
.PN XtResourceQuark
.IN "XtResourceQuark" "" "@DEF@"
causes \fIaddress_id\fP to be interpreted as the result of an
.PN XrmStringToQuark
conversion on the name of a resource,
which is to be converted into an offset from the widget base.
.PN XtWidgetBaseOffset
.IN "XtWidgetBaseOffset" "" "@DEF@"
is similar to
.PN XtBaseOffset
except that it
searches for the closest windowed ancestor if the object is not
of a subclass of
Core
(See Chapter 12).
.PN XtProcedureArg
.IN "XtProcedureArg" "" "@DEF@"
specifies that \fIaddress_id\fP is a pointer to a procedure to
be invoked to return the conversion argument.  If
.PN XtProcedureArg
is specified, \fIaddress_id\fP must contain
the address of a function of type
.PN XtConvertArgProc .
.IN "XtConvertArgProc" "" "@DEF@"
.FD 0
typedef void (*XtConvertArgProc)(Widget, Cardinal*, XrmValue*);
.br
      Widget \fIobject\fP;
.br
      Cardinal *\fIsize\fP;
.br
      XrmValue *\fIvalue\fP;
.FN
.IP \fIobject\fP 1i
Passes the object for which the resource is being
converted, or NULL if the converter was invoked by
.PN XtCallConverter
or
.PN XtDirectConvert .
.IP \fIsize\fP 1i
Passes a pointer to the \fIsize\fP field from the
.PN XtConvertArgRec .
.IP \fIvalue\fP 1i
Passes a pointer to a descriptor into which the procedure
must store the conversion argument.
.LP
When invoked, the
.PN XtConvertArgProc
procedure must derive a conversion
argument and store the address and size of the argument in the location
pointed to by \fIvalue\fP.
.LP
In order to permit reentrancy, the
.PN XtConvertArgProc
should return the address of storage whose lifetime is no shorter than the
lifetime of \fIobject\fP.  If \fIobject\fP is NULL, the lifetime of the conversion
argument must be no shorter than the lifetime of the resource with
which the conversion argument is associated.  The \*(xI do not
guarantee to copy this storage but do guarantee not to reference it if
the resource is removed from the conversion cache.
.LP
The following example illustrates how to register the CvtStringToPixel 
routine given earlier:
.LP
.Ds
.TA .2i 3i
.ta .2i 3i
static XtConvertArgRec colorConvertArgs[] = {
	{XtWidgetBaseOffset, (XtPointer)XtOffset(Widget, core.screen),  sizeof(Screen*)},
	{XtWidgetBaseOffset, (XtPointer)XtOffset(Widget, core.colormap),sizeof(Colormap)}
};

XtSetTypeConverter(XtRString, XtRPixel, CvtStringToPixel,
    colorConvertArgs, XtNumber(colorConvertArgs), XtCacheByDisplay, NULL);
.De
.LP
The conversion argument descriptors
.PN colorConvertArgs
and
.PN screenConvertArg
are predefined by the \*(xI.  Both take the
values from the closest windowed ancestor if the object is not of a
subclass of
Core.
The
.PN screenConvertArg
descriptor puts the widget's \fIscreen\fP field into \fIargs\fP[0].  The
.PN colorConvertArgs
descriptor puts the widget's \fIscreen\fP field into \fIargs\fP[0],
and the widget's \fIcolormap\fP field into \fIargs\fP[1].
.LP
Conversion routines should not just put a descriptor for the address of the
base of the widget into \fIargs\fP[0] and use that in the routine.
They should pass in the actual values on which the conversion depends on.
By keeping the dependencies of the conversion procedure specific,
it is more likely that subsequent conversions will find what they need
in the conversion cache.
This way the cache is smaller and has fewer and more widely applicable entries.
.LP
If any conversion arguments of type
.PN XtBaseOffset ,
.PN XtResourceString ,
.PN XtResourceQuark ,
and
.PN XtWidgetBaseOffset
are specified for conversions performed by
.PN XtGetApplicationResources ,
.PN XtGetSubresources ,
.PN XtVaGetApplicationResources
or
.PN XtVaGetSubresources ,
the arguments are
computed with respect to the specified widget, not the base address or
resource list specified in the call.
.LP
If the
.PN XtConvertArgProc
modifies the resource database,
the changes affect any in-progress widget creation,
.PN XtGetApplicationResources ,
or
.PN XtGetSubresources
in an implementation-defined manner; however, insertion of new entries
or changes to existing entries is allowed and will not directly cause
an error.

.NH 3
Resource Converter Invocation
.XS
\fB\*(SN Resource Converter Invocation\fP
.XE
.LP
All resource-fetching routines (for example,
.PN XtGetSubresources ,
.PN XtGetApplicationResources ,
and so on) call resource converters if the resource database or
varargs list specifies a value
that has a different representation from the desired representation or if the
widget's default resource value representation is different from the desired
representation.
.sp
.LP
To invoke explicit resource conversions, use
.PN XtConvertAndStore
or
.PN XtCallConverter .
.sp
.Ds 0
typedef XtPointer XtCacheRef;
.De
.IN "XtCallConverter" "" "@DEF@"
.FD 0
Boolean XtCallConverter( \fIdisplay\fP, \fIconverter\fP, \
\fIconversion_args\fP, \fInum_args\fP, \fIfrom\fP, \fIto_in_out\fP,
                                              \fIcache_ref_return\fP )
.br
      Display* \fIdisplay\fP;
.br
      XtTypeConverter \fIconverter\fP;
.br
      XrmValuePtr \fIconversion_args\fP;
.br
      Cardinal \fInum_args\fP;
.br
      XrmValuePtr \fIfrom\fP;
.br
      XrmValuePtr \fIto_in_out\fP;
.br
      XtCacheRef *\fIcache_ref_return\fP;
.FN
.IP \fIdisplay\fP 1.5i
Specifies the display with which the conversion is to be associated.
.IP \fIconverter\fP 1.5i
Specifies the conversion procedure to be called.
.IP \fIconversion_args\fP 1.5i
Specifies the additional conversion arguments needed
to perform the conversion, or NULL.
.IP \fInum_args\fP 1.5i
Specifies the number of entries in \fIconversion_args\fP.
.IP \fIfrom\fP 1.5i
Specifies a descriptor for the source value.
.IP \fIto_in_out\fP 1.5i
Returns the converted value.
.IP \fIcache_ref_return\fP 1.5i
Returns a conversion cache id.
.LP
The
.PN XtCallConverter
function looks up the
specified type converter in the application context associated with
the display and, if the converter was not registered or was registered
with cache type
.PN XtCacheAll
or
.PN XtCacheByDisplay
looks in the conversion cache to see if this conversion procedure
has been called with the specified conversion arguments.  If so, it
checks the success status of the prior call, and if
the conversion failed,
.PN XtCallConverter
returns
.PN False
immediately;
otherwise it checks the size specified in the \fIto\fP argument and, if it is
greater than or equal to the size stored in the cache, copies the
information stored in the cache into the location specified by
\fIto->addr\fP, stores the cache size into \fIto->size\fP, and returns
.PN True .
If the size specified in the \fIto\fP argument is smaller than the size stored
in the cache,
.PN XtCallConverter
copies the cache size into \fIto->size\fP and returns
.PN False .
If the converter was registered with cache type
.PN XtCacheNone
or no value was found in the conversion cache,
.PN XtCallConverter
calls the converter and, if it was not registered with cache type
.PN XtCacheNone ,
enters the result in the cache.  
.PN XtCallConverter
then returns what the converter returned.
.LP
The \fIcache_ref_return\fP field specifies storage allocated by the caller in which
an opaque value will be stored.  If the type converter has been
registered with the
.PN XtCacheRefCount
modifier and if the value returned
in \fIcache_ref_return\fP is non-NULL, then the caller should store the
\fIcache_ref_return\fP value in order to decrement the reference count when
the converted value is no longer required.  The \fIcache_ref_return\fP
argument should be
NULL if the caller is unwilling or unable to store the
value.
.sp
.LP
To explicitly decrement the reference counts for resources obtained
from
.PN XtCallConverter ,
use
.PN XtAppReleaseCacheRefs .
.IN "XtAppReleaseCacheRefs" "" "@DEF@"
.FD 0
void XtAppReleaseCacheRefs(\fIapp_context\fP, \fIrefs\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtCacheRef *\fIrefs\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIrefs\fP 1i
Specifies the list of cache references to be released.
.LP
.PN XtAppReleaseCacheRefs
decrements the reference count for the
conversion entries identified by the \fIrefs\fP argument.
This argument is a
pointer to a NULL-terminated list of
.PN XtCacheRef
values.  If any reference
count reaches zero, the destructor, if any, will be called and
the resource removed from the conversion cache.
.sp
.LP
As a convenience to clients needing to explicitly decrement reference
counts via a callback function, the \*(xI define two callback
procedures,
.PN XtCallbackReleaseCacheRef
and
.PN XtCallbackReleaseCacheRefList .
.IN "XtCallbackReleaseCacheRef" "" "@DEF@"
.FD 0
void XtCallbackReleaseCacheRef(\fIobject\fP, \fIclient_data\fP, \fIcall_data\fP)
.br
      Widget \fIobject\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtPointer \fIcall_data\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object with which the resource is associated.
.IP \fIclient_data\fP 1i
Specifies the conversion cache entry to be released.
.IP \fIcall_data\fP 1i
Is ignored.
.LP
This callback procedure may be added to a callback list to release a
previously returned
.PN XtCacheRef
value.  When adding the callback, the
callback \fIclient_data\fP argument must be specified as the value of the
.PN XtCacheRef
data cast to type
.PN XtPointer .
.sp
.IN "XtCallbackReleaseCacheRefList" "" "@DEF@"
.FD 0
void XtCallbackReleaseCacheRefList(\fIobject\fP, \fIclient_data\fP, \fIcall_data\fP)
.br
      Widget \fIobject\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtPointer \fIcall_data\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object with which the resources are associated.
.IP \fIclient_data\fP 1i
Specifies the conversion cache entries to be released.
.IP \fIcall_data\fP 1i
Is ignored.
.LP
This callback procedure may be added to a callback list to release a
list of previously returned
.PN XtCacheRef
values.  When adding the
callback, the callback \fIclient_data\fP argument must be specified as a
pointer to a NULL-terminated list of
.PN XtCacheRef
values.
.sp
.LP
To lookup and call a resource converter, copy the resulting value,
and free a cached resource when a widget is destroyed, use
.PN XtConvertAndStore .
.IN "XtConvertAndStore" "" "@DEF@"
.FD 0
Boolean XtConvertAndStore(\fIobject\fP, \fIfrom_type\fP, \fIfrom\fP, \
\fIto_type\fP, \fIto_in_out\fP)
.br
      Widget \fIobject\fP;
.br
      String \fIfrom_type\fP;
.br
      XrmValuePtr \fIfrom\fP;
.br
      String \fIto_type\fP;
.br
      XrmValuePtr \fIto_in_out\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object to use for additional arguments, if any are needed,
and the destroy callback list.  \*(oI
.IP \fIfrom_type\fP 1i
Specifies the source type.
.IP \fIfrom\fP 1i
Specifies the value to be converted.
.IP \fIto_type\fP 1i
Specifies the destination type.
.IP \fIto_in_out\fP 1i
Specifies a descriptor for storage into which the converted value
will be returned.
.LP
The
.PN XtConvertAndStore
function looks up the type converter registered
to convert \fIfrom_type\fP to \fIto_type\fP, computes any additional arguments
needed, and then calls
.PN XtCallConverter
(or
.PN XtDirectConvert
if an old-style converter was registered with
.PN XtAddConverter
or
.PN XtAppAddConverter ;
see Appendix C) with the \fIfrom\fP and \fIto_in_out\fP arguments.  The
\fIto_in_out\fP argument specifies the size and location into which the
converted value will be stored and is passed directly to the
converter.  If the location is specified as NULL, it will be replaced
with a pointer to private storage and the size will be returned in the
descriptor.  The caller is expected to copy this private storage
immediately and must not modify it in any way.  If a non-NULL location
is specified, the caller must allocate sufficient storage to hold the
converted value and must also specify the size of that storage in the
descriptor.
The \fIsize\fP field will be modified on return to indicate the actual
size of the converted data.
If the conversion succeeds,
.PN XtConvertAndStore
returns
.PN True ;
otherwise, it returns
.PN False .
.LP
.PN XtConvertAndStore
adds
.PN XtCallbackReleaseCacheRef
.IN "destroyCallback"
to the destroyCallback list of the specified object if the conversion
returns an
.PN XtCacheRef
value.  The resulting resource should not be referenced
after the object has been destroyed.
.LP
.PN XtCreateWidget
performs processing equivalent to
.PN XtConvertAndStore
when initializing the object instance.  Because there is extra memory
overhead required to implement reference counting, clients may
distinguish those objects that are never destroyed before the
application exits from those that may be destroyed and whose
resources should be deallocated.
.LP
To specify whether reference counting is to be enabled for the
resources of a particular object when the object is created, the
client can specify a value for the
.PN Boolean
resource
XtNinitialResourcesPersistent,
.IN "XtNinitialResourcesPersistent" "" "@DEF@"
class
XtCInitialResourcesPersistent.
.LP
When
.PN XtCreateWidget
is called, if this resource is not specified as
.PN False
in either the arglist or the resource database, then the
resources referenced by this object are not reference-counted, regardless of
how the type converter may have been registered.  The effective
default value is
.PN True ;
thus clients that expect to destroy one or
more objects and want resources deallocated must explicitly specify
.PN False
for
.IN XtNinitialResourcesPersistent
XtNinitialResourcesPersistent.
.LP
The resources are still freed and destructors called when
.PN XtCloseDisplay
is called if the conversion was registered as
.PN XtCacheByDisplay .

.NH 2
Reading and Writing Widget State
.XS
\fB\*(SN Reading and Writing Widget State\fP
.XE
.LP
Any resource field in a widget can be read or written by a client.
On a write operation,
the widget decides what changes it will actually allow and updates all
derived fields appropriately.

.NH 3
Obtaining Widget State
.XS
\fB\*(SN Obtaining Widget State\fP
.XE
.LP
To retrieve the current values of resources associated with a
widget instance, use
.PN XtGetValues .
.IN "XtGetValues" "" "@DEF@"
.FD 0
void XtGetValues(\fIobject\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIobject\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object whose resource values are to be returned.  \*(oI
.IP \fIargs\fP 1i
Specifies the argument list of name/address pairs that contain the
resource names and the addresses into which the resource values are to
be stored.
The resource names are widget-dependent.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtGetValues
function starts with the resources specified for the Object class
and proceeds down the subclass chain to the class of the object.
The \fIvalue\fP field of a passed argument list must contain the
address into which to copy the contents of the corresponding
object instance field.  If the field is a pointer type, the lifetime
of the pointed-to data is defined by the object class.  For the
\*(xI-defined resources, the following lifetimes apply
.IP \(bu 3
Not valid following any operation that modifies the resource:
.RS
.IP \- 3
XtNchildren resource of composite widgets.
.IP \- 3
All resources of representation type XtRCallback.
.RE
.IP \(bu 3
Remain valid at least until the widget is destroyed:
.RS
.IP \- 3
XtNaccelerators, XtNtranslations.
.RE
.IP \(bu 3
Remain valid until the Display is closed:
.RS
.IP \- 3
XtNscreen.
.RE
.LP
It is the caller's responsibility
to allocate and deallocate storage for the copied data
according to the size of the
resource representation type used within the object.
.LP
If the class of the object's parent is a subclass of
.PN constraintWidgetClass ,
.PN XtGetValues
then fetches the values for any constraint resources requested.
It starts with the constraint resources specified for
.PN constraintWidgetClass
and proceeds down the subclass chain to the parent's constraint resources.
If the argument list contains a resource name that is not found in any of the
resource lists searched, 
the value at the corresponding address is not modified.
.IN "get_values_hook procedure"
If any get_values_hook procedures in the
object's class or superclass records are non-NULL, 
they are called in superclass-to-subclass order after
all the resource values have been fetched by
.PN XtGetValues .
Finally, if the object's parent is a
subclass of
.PN constraintWidgetClass ,
and if any of the parent's class or
superclass records have declared
.PN ConstraintClassExtension
records in
the Constraint class part \fIextension\fP field with a record type of
.PN \s-1NULLQUARK\s+1
and if the \fIget_values_hook\fP field in the extension record is non-NULL,
.PN XtGetValues
calls the get_values_hook procedures in superclass-to-subclass order.
This permits a Constraint parent to provide
nonresource data via
.PN XtGetValues .
.LP
Get_values_hook procedures may modify the data stored at the
location addressed by the \fIvalue\fP field, including (but not
limited to) making a copy of data whose resource representation is a
pointer.  None of the \*(xI-defined object classes copy
data in this manner.  Any operation that modifies the queried
object resource may invalidate the pointed-to data.

.sp
.LP
To retrieve the current values of resources associated with a widget
instance using varargs lists, use
.PN XtVaGetValues .
.IN "XtVaGetValues" "" "@DEF@"
.FD 0
void XtVaGetValues(\fIobject\fP, ...)
.br
      Widget \fIobject\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object whose resource values are to be returned.  \*(oI
.IP ... 1i
Specifies the variable argument list for the resources to
be returned.
.LP
.PN XtVaGetValues
is identical in function to
.PN XtGetValues
with the \fIargs\fP
and \fInum_args\fP parameters replaced by a varargs list, as described in
Section 2.5.1.  All value entries in the list must specify pointers to
storage allocated by the caller to which the resource value will be
copied.  It is the caller's responsibility to ensure that sufficient
storage is allocated.  If
.PN XtVaTypedArg
is specified, the \fItype\fP argument
specifies the representation desired by the caller and \fIthe\fP size argument
specifies the number of bytes allocated to store the result of the
conversion.  If the size is insufficient, a warning message is issued
and the list entry is skipped.

.NH 4
Widget Subpart Resource Data: the get_values_hook Procedure
.XS
\*(SN Widget Subpart Resource Data: the get_values_hook Procedure
.XE
.LP
Widgets that have subparts can return resource values from them through
.PN XtGetValues
by supplying a get_values_hook procedure.
The get_values_hook procedure pointer is of type
.PN XtArgsProc .
.IN "get_values_hook procedure" "" "@DEF@"
.FD 0
typedef void (*XtArgsProc)(Widget, ArgList, Cardinal*);
.br
      Widget \fIw\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal *\fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget whose subpart resource values are to be retrieved.
.IP \fIargs\fP 1i
Specifies the argument list that was passed to
.PN XtGetValues
or the transformed varargs list passed to
.PN XtVaGetValues .
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The widget with subpart resources should call
.PN XtGetSubvalues
in the get_values_hook procedure
and pass in its subresource list and the \fIargs\fP and \fInum_args\fP parameters.

.NH 4
Widget Subpart State
.XS
\*(SN Widget Subpart State
.XE
.LP
To retrieve the current values of subpart resource data associated with a
widget instance, use
.PN XtGetSubvalues .
For a discussion of subpart resources,
see Section 9.4.
.IN "XtGetSubvalues" "" "@DEF@"
.FD 0
void XtGetSubvalues(\fIbase\fP, \fIresources\fP, \fInum_resources\fP, \
\fIargs\fP, \fInum_args\fP)
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure for which the
resources should be retrieved.
.IP \fIresources\fP 1i
Specifies the subpart resource list.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP \fIargs\fP 1i
Specifies the argument list of name/address pairs that contain the
resource names and the addresses into which the resource values are to
be stored.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtGetSubvalues
function obtains resource values from the structure identified by \fIbase\fP.
The \fIvalue\fP field in each argument entry must contain the address into
which to store the corresponding resource value.  It is the caller's
responsibility to allocate and deallocate this storage according to
the size of the resource representation type used within the subpart.
If the argument list contains a resource name that is not found in the
resource list, the value at the corresponding address is not modified.

.sp
.LP
To retrieve the current values of subpart resources associated with
a widget instance using varargs lists, use
.PN XtVaGetSubvalues .
.IN "XtVaGetSubvalues" "" "@DEF@"
.FD 0
void XtVaGetSubvalues(\fIbase\fP, \fIresources\fP, \fInum_resources\fP, ...)
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.FN
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure for which the
resources should be retrieved.
.IP \fIresources\fP 1i
Specifies the subpart resource list.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP ... 1i
Specifies a variable argument list of name/address pairs that
contain the resource names and the addresses into which the resource
values are to be stored.
.LP
.PN XtVaGetSubvalues
is identical in function to
.PN XtGetSubvalues
with the
\fIargs\fP and \fInum_args\fP parameters replaced by a varargs list, as described
in Section 2.5.1.
.PN XtVaTypedArg
is not supported for
.PN XtVaGetSubvalues .
If
.PN XtVaTypedArg
is specified in the list, a warning message is issued
and the entry is then ignored.

.NH 3
Setting Widget State
.XS
\fB\*(SN Setting Widget State\fP
.XE
.LP
To modify the current values of resources associated with a widget
instance, use
.PN XtSetValues .
.IN "XtSetValues" "" "@DEF@"
.FD 0
void XtSetValues(\fIobject\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIobject\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object whose resources are to be modified.  \*(oI
.IP \fIargs\fP 1i
Specifies the argument list of name/value pairs that contain the
resources to be modified and their new values.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtSetValues
function starts with the resources specified for the 
Object
class fields and proceeds down the subclass chain to the object.
At each stage, it replaces the \fIobject\fP resource fields with any values
specified in the argument list.
.PN XtSetValues
then calls the set_values procedures for the object in superclass-to-subclass 
order.
.IN "set_values_hook procedure"
If the object has any non-NULL \fIset_values_hook\fP fields,
these are called immediately after the
corresponding set_values procedure.
This procedure permits subclasses to set subpart data via
.PN XtSetValues .
.LP
If the class of the object's parent is a subclass of
.PN constraintWidgetClass ,
.PN XtSetValues
also updates the object's constraints.
It starts with the constraint resources specified for
.PN constraintWidgetClass
and proceeds down the subclass chain to the parent's class.
At each stage, it replaces the constraint resource fields with any
values specified in the argument list.
It then calls the constraint set_values procedures from
.PN constraintWidgetClass
down to the parent's class.
The constraint set_values procedures are called with widget arguments,
as for all set_values procedures, not just the constraint records,
so that they can make adjustments to the desired values based
on full information about the widget.  Any arguments specified that
do not match a resource list entry are silently ignored.
.LP
If the object is of a subclass of
RectObj,
.PN XtSetValues
determines if a geometry request is needed by comparing the old object to
the new object.
If any geometry changes are required,
.PN XtSetValues
restores the original geometry and makes the request on behalf of the widget.
If the geometry manager returns
.PN XtGeometryYes ,
.PN XtSetValues
calls the object's resize procedure.
If the geometry manager returns
.PN XtGeometryDone ,
.PN XtSetValues
continues, as the object's resize procedure should have been called
by the geometry manager.
If the geometry manager returns
.PN XtGeometryNo ,
.PN XtSetValues
ignores the geometry request and continues.
If the geometry manager returns
.PN XtGeometryAlmost ,
.PN XtSetValues
calls the set_values_almost procedure,
which determines what should be done.
.PN XtSetValues
then repeats this process,
deciding once more whether the geometry manager should be called.
.LP
Finally, if any of the set_values procedures returned 
.PN True ,
and the widget is realized,
.PN XtSetValues
causes the widget's expose procedure to be invoked by calling
.PN XClearArea
on the widget's window.
.sp
.LP
To modify the current values of resources associated with a widget
instance using varargs lists, use
.PN XtVaSetValues .
.IN "XtVaSetValues" "" "@DEF@"
.FD 0
void XtVaSetValues(\fIobject\fP, ...)
.br
      Widget \fIobject\fP;
.FN
.IP \fIobject\fP 1i
Specifies the object whose resources are to be modified.  \*(oI
.IP ... 1i
Specifies the variable argument list of name/value pairs that
contain the resources to be modified and their new values.
.LP
.PN XtVaSetValues
is identical in function to
.PN XtSetValues
with the \fIargs\fP and \fInum_args\fP parameters replaced by a varargs list, as
described in Section 2.5.1.

.NH 4
Widget State: the set_values Procedure
.XS
\*(SN Widget State: the set_values Procedure
.XE
.LP
The set_values procedure pointer in a widget class is of type
.PN XtSetValuesFunc .
.IN "XtSetValuesFunc" "" "@DEF@"
.IN "set_values procedure" "" "@DEF@"
.FD 0
typedef Boolean (*XtSetValuesFunc)(Widget, Widget, Widget, ArgList, Cardinal*);
.br
      Widget \fIcurrent\fP;
.br
      Widget \fIrequest\fP;
.br
      Widget \fInew\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal *\fInum_args\fP;
.FN
.IP \fIcurrent\fP 1i
Specifies a copy of the widget as it was before the
.PN XtSetValues
call.
.IP \fIrequest\fP 1i
Specifies a copy of the widget with all values changed as asked for by the
.PN XtSetValues
call before any class set_values procedures have been called.
.IP \fInew\fP 1i
Specifies the widget with the new values that are actually allowed.
.IP \fIargs\fP 1i
Specifies the argument list passed to
.PN XtSetValues
or the transformed argument list passed to
.PN XtVaSetValues .
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The set_values procedure should recompute any field
derived from resources that are changed
(for example, many GCs depend on foreground and background pixels).
If no recomputation is necessary and if none of the resources specific to a
subclass require the window to be redisplayed when their values are changed,
you can specify NULL for the \fIset_values\fP field in the class record.
.LP
Like the initialize procedure,
set_values mostly deals only with the fields defined in the subclass,
but it has to resolve conflicts with its superclass,
especially conflicts over width and height.
.LP
Sometimes a subclass may want to overwrite values filled in by its
superclass.
In particular, size calculations of a superclass are often
incorrect for a subclass and, in this case,
the subclass must modify or recalculate fields declared
and computed by its superclass.
.LP
As an example,
a subclass can visually surround its superclass display.
In this case, the width and height calculated by the superclass set_values
procedure are too small and need to be incremented by the size of the surround.
The subclass needs to know if its superclass's size was calculated by the
superclass or was specified explicitly.
All widgets must place themselves into whatever size is explicitly given,
but they should compute a reasonable size if no size is requested.
How does a subclass know the difference between a specified size
and a size computed by a superclass?
.LP
The \fIrequest\fP and \fInew\fP parameters provide the necessary information.
The \fIrequest\fP widget is a copy of the widget, updated as originally requested.
The \fInew\fP widget starts with the values in the request,
but it has additionally been updated by all superclass set_values
procedures called so far.
A subclass set_values procedure can compare these two to resolve
any potential conflicts.
The set_values procedure need not refer to the \fIrequest\fP widget
unless it must resolve conflicts between the \fIcurrent\fP and \fInew\fP widgets.
Any changes the widget needs to make, including geometry changes,
should be made in the \fInew\fP widget.
.LP
In the above example,
the subclass with the visual surround can see
if the \fIwidth\fP and \fIheight\fP in the \fIrequest\fP widget are zero.
If so,
it adds its surround size to the \fIwidth\fP and
\fIheight\fP fields in the \fInew\fP widget.
If not, it must make do with the size originally specified.
In this case, zero is a special value defined by the class to permit
the application to invoke this behavior.
.LP
The \fInew\fP widget is the actual widget instance record.
Therefore,
the set_values procedure should do all its work on the \fInew\fP widget;
the \fIrequest\fP widget should never be modified.
If the set_values procedure needs to call any routines that operate on
a widget, it should specify \fInew\fP as the widget instance.
.LP
Before calling the set_values procedures, the \*(xI modify the
resources of the \fIrequest\fP widget according to the contents of the arglist;
if the widget names all its resources in the class resource list, it is
never necessary to examine the contents of \fIargs\fP.
.LP
Finally, the set_values procedure must return a Boolean that indicates whether
the widget needs to be redisplayed.
Note that a change in the geometry fields alone does not require
the set_values procedure to return 
.PN True ;
the X server will eventually generate an
.PN Expose
event, if necessary.
After calling all the set_values procedures,
.PN XtSetValues
forces a redisplay by calling
.PN XClearArea
if any of the set_values procedures returned 
.PN True .
Therefore, a set_values procedure should not try to do its own redisplaying.
.LP
Set_values procedures should not do any work in response to changes in
geometry because
.PN XtSetValues
eventually will perform a geometry request, and that request might be denied.
If the widget actually changes size in response to a
call to
.PN XtSetValues ,
its resize procedure is called.
Widgets should do any geometry-related work in their resize procedure.
.LP
Note that it is permissible to call
.PN XtSetValues
before a widget is realized.
Therefore, the set_values procedure must not assume that the widget is realized.

.NH 4
Widget State: the set_values_almost Procedure
.XS
\*(SN Widget State: the set_values_almost Procedure
.XE
.LP
The set_values_almost procedure pointer in the widget class record is of type
.PN XtAlmostProc .
.IN "set_values_almost procedure" "" "@DEF@"
.IN "XtAlmostProc" "" "@DEF@"
.FD 0
typedef void (*XtAlmostProc)(Widget, Widget, XtWidgetGeometry*, \
XtWidgetGeometry*);
.br
      Widget \fIold\fP;
.br
      Widget \fInew\fP;
.br
      XtWidgetGeometry *\fIrequest\fP;
.br
      XtWidgetGeometry *\fIreply\fP;
.FN
.IP \fIold\fP 1i
Specifies a copy of the object as it was before the
.PN XtSetValues
call.
.IP \fInew\fP 1i
Specifies the object instance record.
.IP \fIrequest\fP 1i
Specifies the original geometry request that was sent to the geometry
manager that caused
.PN XtGeometryAlmost
to be returned.
.IP \fIreply\fP 1i
Specifies the compromise geometry that was returned by the geometry
manager with
.PN XtGeometryAlmost .
.LP
Most classes inherit the set_values_almost procedure from their superclass by
specifying 
.PN XtInheritSetValuesAlmost 
in the class initialization.
The
set_values_almost procedure in
.PN rectObjClass
accepts the compromise suggested.
.LP
The set_values_almost procedure is called when a client tries to set a widget's
geometry by means of a call to
.PN XtSetValues ,
and the geometry manager cannot
satisfy the request but instead returns
.PN XtGeometryNo
or
.PN XtGeometryAlmost
and a compromise geometry.
The \fInew\fP object is the actual instance record.  The \fIx\fP, \fIy\fP,
\fIwidth\fP, \fIheight\fP,
and \fIborder_width\fP fields contain the original values as they were
before the
.PN XtSetValues
call and all other fields contain the new
values.  The \fIrequest\fP parameter contains the new geometry request that
was made to the parent.  The \fIreply\fP parameter contains
\fIreply->request_mode\fP equal to zero if the parent returned
.PN XtGeometryNo
and contains the parent's compromise geometry otherwise.  The
set_values_almost procedure takes the original geometry and the 
compromise geometry and determines if the compromise is
acceptable or whether
to try a different compromise.
It returns its results in the \fIrequest\fP parameter,
which is then sent back to the geometry manager for another try.
To accept the compromise, the procedure must copy the contents
of the \fIreply\fP geometry into the \fIrequest\fP geometry; to attempt an
alternative geometry, the procedure may modify any part of the \fIrequest\fP
argument; to terminate the geometry negotiation and retain the
original geometry, the procedure must set \fIrequest->request_mode\fP to
zero.  The geometry fields of the \fIold\fP and \fInew\fP instances must not be modified
directly.

.NH 4
Widget State: the ConstraintClassPart set_values Procedure
.XS
\*(SN Widget State: the ConstraintClassPart set_values Procedure
.XE
.IN "set_values procedure"
.LP
The constraint set_values procedure pointer is of type
.PN XtSetValuesFunc .
The values passed to the parent's constraint set_values procedure
are the same as those passed to the child's class
set_values procedure.
A class can specify NULL for the \fIset_values\fP field of the
.PN ConstraintPart
if it need not compute anything.
.LP
The constraint set_values procedure should recompute any constraint fields
derived from constraint resources that are changed.
Further, it may modify other widget fields as appropriate.
For example, if a constraint for the maximum height of a widget is changed
to a value smaller than the widget's current height,
the constraint set_values procedure may reset the \fIheight\fP field in the
widget.

.NH 4
Widget Subpart State
.XS
\*(SN Widget Subpart State
.XE
.LP
To set the current values of subpart resources associated with a
widget instance, use
.PN XtSetSubvalues .
For a discussion of subpart resources,
see Section 9.4.
.IN "XtSetSubvalues" "" "@DEF@"
.FD 0
void XtSetSubvalues(\fIbase\fP, \fIresources\fP, \fInum_resources\fP, \
\fIargs\fP, \fInum_args\fP)
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure into which the
resources should be written.
.IP \fIresources\fP 1i
Specifies the subpart resource list.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP \fIargs\fP 1i
Specifies the argument list of name/value pairs that contain the
resources to be modified and their new values.
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The
.PN XtSetSubvalues
function updates the resource fields of the structure identified by
\fIbase\fP.  Any specified arguments that do not match an entry in the
resource list are silently ignored.
.sp
.LP
To set the current values of subpart resources associated with
a widget instance using varargs lists, use
.PN XtVaSetSubvalues .
.IN "XtVaSetSubvalues" "" "@DEF@"
.FD 0 
void XtVaSetSubvalues(\fIbase\fP, \fIresources\fP, \fInum_resources\fP, ...)
.br
      XtPointer \fIbase\fP;
.br
      XtResourceList \fIresources\fP;
.br
      Cardinal \fInum_resources\fP;
.FN
.IP \fIbase\fP 1i
Specifies the base address of the subpart data structure into which the
resources should be written.
.IP \fIresources\fP 1i
Specifies the subpart resource list.
.IP \fInum_resources\fP 1i
Specifies the number of entries in the resource list.
.IP ... 1i
Specifies the variable argument list of name/value pairs that
contain the resources to be modified and their new values.
.LP
.PN XtVaSetSubvalues
is identical in function to
.PN XtSetSubvalues
with the \fIargs\fP and \fInum_args\fP parameters replaced by a varargs list, as
described in Section 2.5.1.
.PN XtVaTypedArg
is not supported for
.PN XtVaSetSubvalues .
If an entry containing
.PN XtVaTypedArg
is specified in the list, a warning message is issued
and the entry is ignored.

.NH 4
Widget Subpart Resource Data: the set_values_hook Procedure
.XS
\*(SN Widget Subpart Resource Data: the set_values_hook Procedure
.XE
.IN "set_values_hook procedure"
.NT
The set_values_hook procedure is obsolete, as the same information
is now available to the set_values procedure.  The procedure has been
retained for those widgets that used it in versions prior to Release 4.
.NE
.LP
Widgets that have a subpart can set the subpart resource values through
.PN XtSetValues
by supplying a set_values_hook procedure.
The set_values_hook procedure pointer in a widget class is of type
.PN XtArgsFunc .
.IN "set_values_hook procedure" "" "@DEF@"
.IN "XtArgsFunc" "" "@DEF@"
.FD 0
typedef Boolean (*XtArgsFunc)(Widget, Arglist, Cardinal*);
.br
      Widget \fIw\fP;
.br
      Arglist \fIargs\fP;
.br
      Cardinal *\fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget whose subpart resource values are to be changed.
.IP \fIargs\fP 1i
Specifies the argument list that was passed to
.PN XtSetValues
or the transformed varargs list passed to
.PN XtVaSetValues .
.IP \fInum_args\fP 1i
Specifies the number of entries in the argument list.
.LP
The widget with subpart resources may call
.PN XtSetValues
from the set_values_hook procedure
and pass in its subresource list and the
\fIargs\fP and \fInum_args\fP parameters.
.bp