[cogl] bitmap: Use the 'copy' blend mode when loading images on Quartz

[Neil Roberts <nroberts src gnome org>]

commit 5ba7f4e6837a539d92cbe45491f79a8926fd6828
Author: Neil Roberts <neil linux intel com>
Date:   Wed Jul 18 11:28:13 2012 +0100

    bitmap: Use the 'copy' blend mode when loading images on Quartz
    
    When loading images on Quartz, the image is rendered into a bitmap
    context using a buffer allocated with
    _cogl_bitmap_new_with_malloc_buffer. However this buffer is not
    initialised and by default Quartz will blend the source image with the
    destination so if there are transparent parts in the source image it
    will leave garbage in the destination. This patch changes the blend
    mode to 'copy' so that it won't try to blend.
    
    Before 5b785dd4 the buffer was cleared because it was allocated with
    g_malloc0 so it was working in that case. Presumably it should be more
    efficient to disable blending and avoid the clear though.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=680124
    
    Reviewed-by: Robert Bragg <robert linux intel com>

 cogl/cogl-bitmap-pixbuf.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/cogl/cogl-bitmap-pixbuf.c b/cogl/cogl-bitmap-pixbuf.c
index d30a851..ba31c56 100644
--- a/cogl/cogl-bitmap-pixbuf.c
+++ b/cogl/cogl-bitmap-pixbuf.c
@@ -139,6 +139,8 @@ _cogl_bitmap_from_file (CoglContext *ctx,
                                           kCGImageAlphaPremultipliedFirst);
   CGColorSpaceRelease (color_space);
 
+  CGContextSetBlendMode (bitmap_context, kCGBlendModeCopy);
+
   {
     const CGRect rect = {{0, 0}, {width, height}};