Win32: Fix up src coords before calling AlphaBlend/BitBlt to avoid invalid calls

Fixes up src coords and width/height before calling AlphaBlend/BitBlt; it's
an error to try to use a region that extents outside of the source surface
as a source DC.

Doesn't repair the extra region relative to the operator -- e.g. regions
outside of an ARGB source surface with SOURCE operator should be cleared
to fully transparent black in the destination.
(cherry picked from bc19c5b64b0e38e9d20045907d7b47d79f6afc60 commit)
(cherry picked from 68ed40b6da242816a43cd68cc2c7feb779cf0acf commit)

1 files changed, 29 insertions, 2 deletions

diff --git a/src/cairo-win32-surface.c b/src/cairo-win32-surface.c
index df7ec413f..66fc1c48d 100644
--- a/src/cairo-win32-surface.c
+++ b/src/cairo-win32-surface.c
@@ -664,6 +664,33 @@ _cairo_win32_surface_composite (cairo_operator_t	operator,
     if (!integer_transform)
 	return CAIRO_INT_STATUS_UNSUPPORTED;
 
+    /* Fix up src coordinates; the src coords and size must be within the
+     * bounds of the source surface.
+     * XXX the region not covered should be appropriately rendered!
+     * - for OVER/SOURCE with RGB24 source -> opaque black
+     * - for SOURCE with ARGB32 source -> 100% transparent black
+     */
+    src_x += itx;
+    src_y += ity;
+
+    if (src_x < 0) {
+        width += src_x;
+        dst_x -= src_x;
+        src_x = 0;
+    }
+
+    if (src_y < 0) {
+        height += src_y;
+        dst_y -= src_y;
+        src_y = 0;
+    }
+
+    if (src_x + width > src->extents.width)
+        width = src->extents.width - src_x;
+
+    if (src_y + height > src->extents.height)
+        height = src->extents.height - src_y;
+
     if (alpha == 255 &&
 	src->format == dst->format &&
 	(operator == CAIRO_OPERATOR_SOURCE ||
@@ -673,7 +700,7 @@ _cairo_win32_surface_composite (cairo_operator_t	operator,
 		     dst_x, dst_y,
 		     width, height,
 		     src->dc,
-		     src_x + itx, src_y + ity,
+		     src_x, src_y,
 		     SRCCOPY))
 	    return _cairo_win32_print_gdi_error ("_cairo_win32_surface_composite");
 
@@ -685,7 +712,7 @@ _cairo_win32_surface_composite (cairo_operator_t	operator,
 	       operator == CAIRO_OPERATOR_OVER) {
 
 	return _composite_alpha_blend (dst, src, alpha,
-				       src_x + itx, src_y + ity,
+				       src_x, src_y,
 				       dst_x, dst_y, width, height);
     }