path: root/xc/programs/Xserver/hw/xfree86/doc/README.DGA

                   XFree86-DGA Extension version 2.0

   The XFree86-DGA extension is an X server extension for allowing client
programs direct access to the video frame buffer.

   This is a brief description of the programming interface for the
XFree86-DGA extension.  This describes version 2.0, which is the second
official version.  The functions described here are found in the library
libXxf86dga.a, and their prototypes are in <X11/extensions/xf86dga.h>.

   XFree86 DGA is not intended as a direct rendering API, but rather,
as a mechanism to "get the X-Server out of the way" so that a direct
rendering API, such as OpenGL, can have full access to the hardware.
With this in mind, DGA does provide clients some direct access to
the hardware without requiring a separate rendering API, but this
access is limited to direct linear framebuffer access.

   DGA is initialized by passing a number corresponding to a valid
XDGAMode to XDGASetMode().  Clients can get a list of valid modes
from XDGAQueryModes().  Each XDGAMode corresponds to a different
framebuffer layout.

typedef struct {
   int num;            
   char *name;          
   float verticalRefresh;
   int flags;           
   int imageWidth;      
   int imageHeight;
   int pixmapWidth;     
   int pixmapHeight;    
   int bytesPerScanline; 
   int byteOrder;       
   int depth;           
   int bitsPerPixel;
   unsigned long redMask;
   unsigned long greenMask;
   unsigned long blueMask;
   short visualClass;
   int viewportWidth;
   int viewportHeight;
   int xViewportStep;   
   int yViewportStep;
   int maxViewportX;    
   int maxViewportY;
   int viewportFlags;   
} XDGAMode;

   num

	A unique identifying number (num > 0) for the mode.  This is the
	number referenced when initializing the mode.

   name

	The name of the corresponding modeline as given in the XF86Config file.

   verticalRefresh

	The vertical refresh rate for the modeline (in Hz).

   flags
	
	Any of the following may be OR'd together:

	XDGAConcurrentAccess

	   Indicates that concurrent client/server access to the 
	   framebuffer is possible.  If this flag is not set it is
	   very important to call XDGASync() before directly accessing
	   the framebuffer if a call to XDGAFillRectangle(),
	   XDGACopyArea() or XDGACopyTransparentArea() or any Xlib
	   rendering function has been made prior to such accesses.

	XDGASolidFillRect

	   Indicates that XDGAFillRectangle() is supported.

	XDGABlitRect

	   Indicates that XDGACopyArea() is supported.

	XDGABlitTransRect

	   Indicates that XDGACopyTransparentArea() is supported.

	XDGAPixmap

	   Indicates that a Pixmap will be returned when the mode is
	   initialized.  This means that rendering with Xlib is possible
	   for this mode.

	XDGAInterlaced
	XDGADoublescan
	
	   Indicates that the mode is an interlaced or doublescan mode.
	    

   imageWidth
   imageHeight

	The width and height of the framebuffer area accessible by the client.
	This rectangle is always justified to the upper left-hand corner.

   pixmapWidth
   pixmapHeight

	The width and height of the framebuffer area accessible by Xlib.
	This rectangle is always justified to the upper left-hand corner.
	These fields are only valid if the XDGAPixmap flag is set in the
        "flags" field.

   bytesPerScanline
	
	The pitch of the framebuffer in bytes.

   byteOrder

	MSBFirst or LSBFirst.

   depth

	The number of bits in each pixel which contain usable data.

   bitsPerPixel

	The number of bits taken up by each pixel.

   redMask
   greenMask
   blueMask

	The RGB masks.  These do not apply to color-indexed modes.

   visualClass

	TrueColor, PseudoColor, DirectColor, etc...

   viewportWidth
   viewportHeight

	The dimensions of the portion of the framebuffer which will be
	displayed on the screen.

   xViewPortStep
   yViewPortStep

	The granularity of the x,y viewport positioning possible with
	the XDGASetViewport function.

   maxViewportX
   maxViewportY

	The maximimum x and y positions possible with the XDGASetViewport
	function.

   viewportFlags

	Any of the following may be OR'd together:

	XDGAFlipRetrace

	    Indicates that the hardware can switch viewports during
	    the vertical retrace.

	XDGAFlipImmediate

	    Indicates that the hardware can switch viewports immediately
	    without waiting for the vertical retrace.



XDGAMode* XDGAQueryModes(
    Display     *dpy,
    int         screen,
    int         *num
);

   XDGAQueryModes() returns a pointer to an array of XDGAModes which 
are valid for the given screen.  "num" is the number of elements in the
array.  The returned array can be freed with XFree();
  


XDGADevice* XDGASetMode(
    Display     *dpy,
    int         screen,
    int         num
);

   A XDGAMode will be initialized when its "num" is passed to
XDGASetMode().  To exit DGA mode and return to normal server operation,
pass number zero to XDGASetMode().  XDGASetMode() returns a pointer
to an XDGADevice if successful.  The XDGADevice can be freed with
XFree().

	struct {
	    XDGAMode mode;
	    unsigned char *data;
	    Pixmap pixmap;
	} XDGADevice;


    mode

	The XDGAMode structure, identical to the information returned
	by XDGAQueryModes.

    data

	If direct framebuffer access is desired and possible, this field
	will contain a pointer to the mapped framebuffer memory.  Generally,
	this field will be zero unless a call to XDGAOpenFramebuffer()
	is made prior to initialization of the mode.

    pixmap

	If the mode supports Xlib rendering as indicated by XDGAPixmap
	in the flags field, this will contain a Pixmap handle suitable
        for passing as the drawable argument to Xlib functions.  This
	field will be zero if Xlib rendering is not supported.


Bool XDGAQueryExtension(
    Display     *dpy,
    int         *eventBase,
    int         *errorBase
);

    XDGAQueryExtension() checks for the prescence of the extension
and returns the event and error bases.


Bool XDGAQueryVersion(
    Display     *dpy,
    int         *majorVersion,
    int         *minorVersion
);

    XDGAQueryVersion() returns the major and minor version numbers (duh).


Bool XDGAOpenFramebuffer(
    Display     *dpy,
    int         screen
);

void XDGACloseFramebuffer(
    Display     *dpy,
    int         screen
);
   

    XDGAOpenFramebuffer() maps the framebuffer memory.  The client
needs sufficient privledges to be able to do this.

    XDGAOpenFramebuffer() should be called prior to initializing
a dga mode if direct framebuffer access is desired for that mode.
XDGAOpenFramebuffer() does not need to be called if direct framebuffer
access is not required.   If the framebuffer is opened, 
XDGACloseFramebuffer() should be called prior to client exit to 
unmap the memory. 



void XDGAChangePixmapMode(
    Display     *dpy,
    int         screen,
    int         *x,
    int         *y,
    int         mode
);

   In the case where a Pixmap is available for Xlib rendering, this
function allows changing between two pixmap sizes.  The following
values for "mode" are possible.

   XDGAPixmapModeLarge
	
	The pixmap size is defined by the pixmapWidth and pixmapHeight
	fields in the XDGAMode structure.  The "x" and "y" values are
	ignored in this case.

   XDGAPixmapModeSmall
    
	The pixmap size is defined by the viewportWidth and viewportHeight
	fields in the XDGAMode structure.  In this mode, the "x" and "y"
	values specify where in the framebuffer this pixmap rectangle
	is located.  It may be placed anywhere within the Xlib renderable
	region described by the pixmapWidth and pixmapHeight fields in 
	the XDGAMode.  The "x" and "y" values returned are the resultant
	location of the pixmap and may be different from the requested
	x,y location due to platform specific alignment constraints.
	All Xlib rendering is clipped to this pixmap rectangle.


void XDGASetViewport(
    Display     *dpy,
    int         screen,
    int         x,
    int         y,
    int         flags
);

    Set the upper left-hand corner of the rectangle of framebuffer
that is to be displayed on the screen.  Not all locations may be
supported by the hardware and requested locations will be adjusted
according to the xViewPortStep and yViewPortStep fields in the XDGAMode.

    "flags" can be XDGAFlipRetrace or XDGAFlipImmediate to adjust
the viewport location at the next vertical retrace or immediately.
Values other than the supported values advertised in the mode's
viewportFlags field will result in hardware-specific default behavior.
XDGAFlipImmediate will block until the flip is completed. 
XDGAFlipRetrace will generally NOT block so it is necessary to 
monitor the viewport status with XDGAGetViewportStatus().

    FlipImmediate requests during pending FlipRetrace requests
will be ignored.


int XDGAGetViewportStatus(
    Display     *dpy,
    int         screen
);

     
   XDGAGetViewportStatus() keeps track of the XDGASetViewport() 
requests still pending.  The return value of the function will
have consecutive bits set (LSB justified), each bit representing
a pending viewport change.  For example:

     while(XDGAGetViewportStatus(dpy, screen));

   waits for all pending viewport changes to finish.

     while(0x2 & XDGAGetViewportStatus(dpy, screen));

   waits until all but the last viewport changes have completed.


Colormap XDGACreateColormap(
    Display     *dpy,
    int         screen,
    XDGADevice  *device,
    int         alloc
);

void XDGAInstallColormap(
    Display     *dpy,
    int         screen,
    Colormap    cmap
);

   XDGACreateColormap() is similar to the Xlib function XCreateColormap() 
except that it takes an XDGADevice as an argument instead of a Window
and Visual.  Though XCreateColormap() may create useable colormaps in
some cases, XDGACreateColormap() is the prefered method for creating
colormaps in DGA since there may not be an advertised visual compatible
with the DGA device.

   XDGAInstallColormap() must be used to install colormaps in DGA
mode.  XInstallColormap() will not work.



void XDGASelectInput(
    Display     *dpy,
    int         screen,
    long        event_mask
);

   DGA provides its own events.  These can be enabled by calling
XDGASelectInput().  This function is similar to XSelectInput()
and all Xlib Key, Button and Motion masks are supported.


 The following DGA events are defined.

typedef struct {
   int type;		 /* ButtonPress or ButtonRelease + the DGA event base*/
   unsigned long serial; /* # or last request processed by the server */
   Display *display;     /* Display the event was read from */
   int screen;           /* The screen number the event came from */
   Time time;            /* milliseconds */
   unsigned int state;   /* key or button mask */
   unsigned int button;  /* detail */
} XDGAButtonEvent;   

typedef struct {
   int type;             /* KeyPress or KeyRelease + the DGA event base*/
   unsigned long serial; /* # or last request processed by the server */
   Display *display;     /* Display the event was read from */
   int screen;           /* The screen number the event came from */
   Time time;            /* milliseconds */
   unsigned int state;   /* key or button mask */
   unsigned int keycode; /* detail */
} XDGAKeyEvent;

typedef struct {
   int type;             /* MotionNotify + the DGA event base*/
   unsigned long serial; /* # or last request processed by the server */
   Display *display;     /* Display the event was read from */
   int screen;           /* The screen number the event came from */
   Time time;            /* milliseconds */
   unsigned int state;   /* key or button mask */
   int dx;               /* relative pointer motion */
   int dy;               /* relative pointer motion */
} XDGAMotionEvent;


void 
XDGAKeyEventToXKeyEvent(XDGAKeyEvent* dk, XKeyEvent* xk);

   XDGAKeyEventToXKeyEvent() is a helper function to translate 
XDGAKeyEvents into XKeyEvents suitable for use with XLookupKeysym().


void XDGAFillRectangle(
    Display     *dpy,
    int         screen,
    int         x,
    int         y,
    unsigned int        width,
    unsigned int        height,
    unsigned long       color
);


void XDGACopyArea(
    Display     *dpy,
    int         screen,
    int         srcx,
    int         srcy,
    unsigned int        width,
    unsigned int        height,
    int         dstx,
    int         dsty
);


void XDGACopyTransparentArea(
    Display     *dpy,
    int         screen,
    int         srcx,
    int         srcy,
    unsigned int        width,
    unsigned int        height,
    int         dstx,
    int         dsty,
    unsigned long key      /* source pixels of this value will not be copied */
);

   These three functions are included with some reserveration since
DGA is not intended as a rendering API.  These are merely convience
routines and are optionally supported.  The associated flags will
be set in the XDGAMode's "flags" field if these functions are supported.  
These functions will be no-ops otherwise. 

   These functions do not provide direct access to the hardware,
but are merely context-less operations performed by the server.


void XDGASync(
    Display     *dpy,
    int         screen
);

    This function blocks until all server rendering to the framebuffer
completes.  If Xlib or the 3 rendering functions above are used, XDGASync()
must be called before the client directly accesses the framebuffer as
the server rendering is asynchronous with the client and may have not
completed.  This is especially important if the XDGAConcurrentAccess 
flag is not set in the XDGAMode's "flags" field since concurrent access 
by the server and client may result in a system lockup.





$XFree86: xc/programs/Xserver/hw/xfree86/DGA,v 1.1 1999/11/19 13:54:09 hohndel Exp $