[patch] gl: fix y-axis origin when map_to_image() for non texture GL surface

We need to fix y-axis origin when map a GL surface to image surface for non-texture GL surface.  Test cases: extended-blend-alpha-mask, extended-blend-mask.  Although the image outputs is not right, but the image on the first grid (upper-left corner) is right comparing to image output before patch.

commit d4f720ebb2d21aa53b1e6826f3c0fd1d2b07d70e
Author: Henry (Yu) Song <[email protected]>
Date:   Wed Mar 28 18:03:24 2012 -0700

    gl: when read pixels from non texture surface, we need to invert the y-axis
    origin

diff --git a/src/cairo-gl-surface.c b/src/cairo-gl-surface.c
index 91c860a..7b6c7ff 100644
--- a/src/cairo-gl-surface.c
+++ b/src/cairo-gl-surface.c
@@ -983,6 +983,7 @@ _cairo_gl_surface_map_to_image (void      *abstract_surface,
     unsigned int cpp;
     cairo_bool_t invert;
     cairo_status_t status;
+    int origin = extents->y;
 
     /* Want to use a switch statement here but the compiler gets whiny. */
     if (surface->base.content == CAIRO_CONTENT_COLOR_ALPHA) {
@@ -1063,7 +1064,11 @@ _cairo_gl_surface_map_to_image (void      *abstract_surface,
 	glPixelStorei (GL_PACK_ROW_LENGTH, image->stride / cpp);
     if (invert)
 	glPixelStorei (GL_PACK_INVERT_MESA, 1);
-    glReadPixels (extents->x, extents->y,
+    
+    if (! _cairo_gl_surface_is_texture (surface))
+	origin = surface->height - extents->y - extents->height;
+
+    glReadPixels (extents->x, origin,
 		  extents->width, extents->height,
 		  format, type, image->data);
     if (invert)
--
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