API: map-to-image and create-similar-image

A common requirement is the fast upload of pixel data. In order to
allocate the most appropriate image buffer, we need knowledge of the
destination. The most obvious example is that we could use a
shared-memory region for the image to avoid the transfer cost of
uploading the pixels to the X server. Similarly, gl, win32, quartz...

The other side of the equation is that for manual modification of a
remote surface, it would be more efficient if we can create a similar
image to reduce the transfer costs. This strategy is already followed
for the destination fallbacks and this merely exposes the same
capability for the application fallbacks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 68 insertions, 65 deletions

diff --git a/src/cairo-xlib-surface.c b/src/cairo-xlib-surface.c
index 46ca63ff..9c46a204 100644
--- a/src/cairo-xlib-surface.c
+++ b/src/cairo-xlib-surface.c
@@ -815,51 +815,37 @@ static const int8_t dither_pattern[4][4] = {
 #undef X
 
 
-static cairo_status_t
+static cairo_surface_t *
 _get_image_surface (cairo_xlib_surface_t    *surface,
-		    cairo_rectangle_int_t   *interest_rect,
-		    cairo_image_surface_t  **image_out,
-		    cairo_rectangle_int_t   *image_rect)
+		    const cairo_rectangle_int_t *extents)
 {
     cairo_int_status_t status;
     cairo_image_surface_t *image = NULL;
     XImage *ximage;
-    cairo_rectangle_int_t extents;
     pixman_format_code_t pixman_format;
     cairo_format_masks_t xlib_masks;
     cairo_xlib_display_t *display;
 
-    extents.x = 0;
-    extents.y = 0;
-    extents.width  = surface->width;
-    extents.height = surface->height;
-
-    if (interest_rect) {
-	if (! _cairo_rectangle_intersect (&extents, interest_rect)) {
-	    *image_out = NULL;
-	    return CAIRO_STATUS_SUCCESS;
-	}
-    }
+    assert (extents->x >= 0);
+    assert (extents->y >= 0);
+    assert (extents->x + extents->width <= surface->width);
+    assert (extents->y + extents->height <= surface->height);
 
     status = _cairo_xlib_display_acquire (surface->base.device, &display);
     if (status)
-        return status;
-
-    if (image_rect)
-	*image_rect = extents;
+        return _cairo_surface_create_in_error (status);
 
     /* XXX: This should try to use the XShm extension if available */
 
-    if (surface->use_pixmap == 0)
-    {
+    if (surface->use_pixmap == 0) {
 	cairo_xlib_error_func_t old_handler;
 
 	old_handler = XSetErrorHandler (_noop_error_handler);
 
 	ximage = XGetImage (display->display,
 			    surface->drawable,
-			    extents.x, extents.y,
-			    extents.width, extents.height,
+			    extents->x, extents->y,
+			    extents->width, extents->height,
 			    AllPlanes, ZPixmap);
 
 	XSetErrorHandler (old_handler);
@@ -869,9 +855,7 @@ _get_image_surface (cairo_xlib_surface_t    *surface,
 	 */
 	if (!ximage)
 	    surface->use_pixmap = CAIRO_ASSUME_PIXMAP;
-    }
-    else
-    {
+    } else {
 	surface->use_pixmap--;
 	ximage = NULL;
     }
@@ -892,18 +876,18 @@ _get_image_surface (cairo_xlib_surface_t    *surface,
 
 	pixmap = XCreatePixmap (display->display,
 				surface->drawable,
-				extents.width, extents.height,
+				extents->width, extents->height,
 				surface->depth);
 	if (pixmap) {
 	    XCopyArea (display->display, surface->drawable, pixmap, gc,
-		       extents.x, extents.y,
-		       extents.width, extents.height,
+		       extents->x, extents->y,
+		       extents->width, extents->height,
 		       0, 0);
 
 	    ximage = XGetImage (display->display,
 				pixmap,
 				0, 0,
-				extents.width, extents.height,
+				extents->width, extents->height,
 				AllPlanes, ZPixmap);
 
 	    XFreePixmap (display->display, pixmap);
@@ -1016,8 +1000,8 @@ _get_image_surface (cairo_xlib_surface_t    *surface,
 	data = cairo_image_surface_get_data (&image->base);
 	rowstride = cairo_image_surface_get_stride (&image->base) >> 2;
 	row = (uint32_t *) data;
-	x0 = extents.x + surface->base.device_transform.x0;
-	y0 = extents.y + surface->base.device_transform.y0;
+	x0 = extents->x + surface->base.device_transform.x0;
+	y0 = extents->y + surface->base.device_transform.y0;
 	for (y = 0, y_off = y0 % ARRAY_LENGTH (dither_pattern);
 	     y < ximage->height;
 	     y++, y_off = (y_off+1) % ARRAY_LENGTH (dither_pattern)) {
@@ -1052,13 +1036,11 @@ _get_image_surface (cairo_xlib_surface_t    *surface,
     cairo_device_release (&display->base);
 
     if (unlikely (status)) {
-	if (image) {
-	    cairo_surface_destroy (&image->base);
-	    image = NULL;
-	}
+	cairo_surface_destroy (&image->base);
+	return _cairo_surface_create_in_error (status);
     }
-    *image_out = image;
-    return status;
+
+    return &image->base;
 }
 
 static void
@@ -1391,31 +1373,29 @@ _cairo_xlib_surface_acquire_source_image (void                    *abstract_surf
 					  void                   **image_extra)
 {
     cairo_xlib_surface_t *surface = abstract_surface;
-    cairo_image_surface_t *image;
-    cairo_status_t status;
+    cairo_rectangle_int_t extents;
 
-    status = _get_image_surface (surface, NULL, &image, NULL);
-    if (unlikely (status))
-	return status;
+    extents.x = extents.y = 0;
+    extents.width = surface->width;
+    extents.height = surface->width;
 
-    *image_out = image;
     *image_extra = NULL;
-
-    return CAIRO_STATUS_SUCCESS;
+    *image_out = (cairo_image_surface_t*)_get_image_surface (surface, &extents);
+    return (*image_out)->base.status;
 }
 
 static cairo_surface_t *
 _cairo_xlib_surface_snapshot (void *abstract_surface)
 {
     cairo_xlib_surface_t *surface = abstract_surface;
-    cairo_image_surface_t *image;
-    cairo_status_t status;
+    cairo_rectangle_int_t extents;
 
-    status = _get_image_surface (surface, NULL, &image, NULL);
-    if (unlikely (status))
-	return _cairo_surface_create_in_error (status);
+    extents.x = extents.y = 0;
+    extents.width = surface->width;
+    extents.height = surface->width;
 
-    return &image->base;
+    /* XXX notice the duplication */
+    return _get_image_surface (surface, &extents);
 }
 
 static void
@@ -1426,6 +1406,29 @@ _cairo_xlib_surface_release_source_image (void                   *abstract_surfa
     cairo_surface_destroy (&image->base);
 }
 
+static cairo_surface_t *
+_cairo_xlib_surface_map_to_image (void                    *abstract_surface,
+				  const cairo_rectangle_int_t   *extents)
+{
+    cairo_surface_t *image;
+
+    image = _get_image_surface (abstract_surface, extents);
+    cairo_surface_set_device_offset (image, -extents->y, -extents->y);
+
+    return image;
+}
+
+static cairo_int_status_t
+_cairo_xlib_surface_unmap_image (void *abstract_surface,
+				 cairo_image_surface_t *image)
+{
+    return _draw_image_surface (abstract_surface, image,
+				0, 0,
+				image->width, image->height,
+				image->base.device_transform_inverse.x0,
+				image->base.device_transform_inverse.y0);
+}
+
 static cairo_status_t
 _cairo_xlib_surface_acquire_dest_image (void                    *abstract_surface,
 					cairo_rectangle_int_t   *interest_rect,
@@ -1433,18 +1436,12 @@ _cairo_xlib_surface_acquire_dest_image (void                    *abstract_surfac
 					cairo_rectangle_int_t   *image_rect_out,
 					void                   **image_extra)
 {
-    cairo_xlib_surface_t *surface = abstract_surface;
-    cairo_image_surface_t *image;
-    cairo_status_t status;
-
-    status = _get_image_surface (surface, interest_rect, &image, image_rect_out);
-    if (unlikely (status))
-	return status;
-
-    *image_out = image;
+    if (image_rect_out)
+	*image_rect_out = *interest_rect;
     *image_extra = NULL;
-
-    return CAIRO_STATUS_SUCCESS;
+    *image_out = (cairo_image_surface_t *)
+	_get_image_surface (abstract_surface, interest_rect);
+    return (*image_out)->base.status;
 }
 
 static void
@@ -3138,12 +3135,18 @@ _cairo_xlib_surface_is_similar (void		*surface_a,
 
 static const cairo_surface_backend_t cairo_xlib_surface_backend = {
     CAIRO_SURFACE_TYPE_XLIB,
+    _cairo_xlib_surface_finish,
+
     _cairo_default_context_create,
 
     _cairo_xlib_surface_create_similar,
-    _cairo_xlib_surface_finish,
+    NULL, //_cairo_xlib_surface_create_similar_image, /* XXX shm */
+    _cairo_xlib_surface_map_to_image,
+    _cairo_xlib_surface_unmap_image,
+
     _cairo_xlib_surface_acquire_source_image,
     _cairo_xlib_surface_release_source_image,
+
     _cairo_xlib_surface_acquire_dest_image,
     _cairo_xlib_surface_release_dest_image,
     _cairo_xlib_surface_clone_similar,