pjs/gfx/cairo/copyarea-with-alpha.patch

diff --git a/gfx/cairo/cairo/src/cairo-xlib-surface.c b/gfx/cairo/cairo/src/cairo-xlib-surface.c
--- a/gfx/cairo/cairo/src/cairo-xlib-surface.c
+++ b/gfx/cairo/cairo/src/cairo-xlib-surface.c
@@ -1722,30 +1722,31 @@ _surface_has_alpha (cairo_xlib_surface_t
 	else
 	    return FALSE;
     } else {
 	/* In the no-render case, we never have alpha */
 	return FALSE;
     }
 }
 
-/* Returns true if the given operator and source-alpha combination
- * requires alpha compositing to complete.
+/* Returns true if the given operator and alpha combination requires alpha
+ * compositing to complete on source and destination surfaces with the same
+ * format.  i.e. if a simple bitwise copy is not appropriate.
  */
 static cairo_bool_t
 _operator_needs_alpha_composite (cairo_operator_t op,
-				 cairo_bool_t     destination_has_alpha,
-				 cairo_bool_t     source_has_alpha)
+				 cairo_bool_t     surfaces_have_alpha)
 {
-    if (op == CAIRO_OPERATOR_SOURCE ||
-	(! source_has_alpha &&
-	 (op == CAIRO_OPERATOR_OVER ||
-	  op == CAIRO_OPERATOR_ATOP ||
-	  op == CAIRO_OPERATOR_IN)))
-	return destination_has_alpha;
+    if (op == CAIRO_OPERATOR_SOURCE)
+	return FALSE;
+
+    if (op == CAIRO_OPERATOR_OVER ||
+	op == CAIRO_OPERATOR_IN ||
+	op == CAIRO_OPERATOR_ATOP)
+	return surfaces_have_alpha;
 
     return TRUE;
 }
 
 /* There is a bug in most older X servers with compositing using a
  * untransformed repeating source pattern when the source is in off-screen
  * video memory, and another with repeated transformed images using a
  * general transform matrix. When these bugs could be triggered, we need a
@@ -1843,24 +1844,24 @@ _categorize_composite_operation (cairo_x
  */
 static composite_operation_t
 _recategorize_composite_operation (cairo_xlib_surface_t	      *dst,
 				   cairo_operator_t	       op,
 				   cairo_xlib_surface_t	      *src,
 				   cairo_surface_attributes_t *src_attr,
 				   cairo_bool_t		       have_mask)
 {
-    /* Can we use the core protocol? */
+    /* Can we use the core protocol?  (If _surfaces_compatible, then src and
+     * dst have the same format and _surface_has_alpha is the same for each.)
+     */
     if (! have_mask &&
         src->owns_pixmap &&
-	src->depth == dst->depth &&
+	_surfaces_compatible (src, dst) &&
 	_cairo_matrix_is_integer_translation (&src_attr->matrix, NULL, NULL) &&
-	! _operator_needs_alpha_composite (op,
-					   _surface_has_alpha (dst),
-					   _surface_has_alpha (src)))
+	! _operator_needs_alpha_composite (op, _surface_has_alpha (dst)))
     {
 	if (src_attr->extend == CAIRO_EXTEND_NONE)
 	    return DO_XCOPYAREA;
 
 	if (dst->buggy_repeat && src_attr->extend == CAIRO_EXTEND_REPEAT)
 	    return DO_XTILE;
     }
 
@@ -2211,34 +2212,28 @@ _cairo_xlib_surface_composite (cairo_ope
     cairo_surface_attributes_t	src_attr, mask_attr;
     cairo_xlib_surface_t	*dst = abstract_dst;
     cairo_xlib_surface_t	*src;
     cairo_xlib_surface_t	*mask;
     cairo_int_status_t		status;
     composite_operation_t       operation;
     int				itx, ity;
     cairo_bool_t		is_integer_translation;
-    cairo_bool_t		needs_alpha_composite;
     GC				gc;
 
     if (mask_pattern != NULL && ! CAIRO_SURFACE_RENDER_HAS_COMPOSITE (dst))
 	return UNSUPPORTED ("no support for masks");
 
     operation = _categorize_composite_operation (dst, op, src_pattern,
 						 mask_pattern != NULL);
     if (operation == DO_UNSUPPORTED)
 	return UNSUPPORTED ("unsupported operation");
 
     X_DEBUG ((dst->dpy, "composite (dst=%x)", (unsigned int) dst->drawable));
 
-    needs_alpha_composite =
-	_operator_needs_alpha_composite (op,
-					 _surface_has_alpha (dst),
-					 ! _cairo_pattern_is_opaque (src_pattern));
-
     _cairo_xlib_display_notify (dst->display);
 
     status =
 	_cairo_xlib_surface_acquire_pattern_surfaces (dst,
 						      src_pattern, mask_pattern,
 						      src_x, src_y,
 						      mask_x, mask_y,
 						      width, height,