attempting to fix tranparency in -Tgif:cairo - not there yet

diff --git a/plugin/gd/gvformatter_gd.c b/plugin/gd/gvformatter_gd.c
index 27575c66bf9196c39c52a91f1f10d4cd24937254..f8de542f96537d7de6965b031461d8ea7defd361 100644 (file)
--- a/plugin/gd/gvformatter_gd.c
+++ b/plugin/gd/gvformatter_gd.c
@@ -42,7 +42,7 @@ static void
 cairo_surface_write_to_gd(cairo_surface_t *surface, format_type format, FILE *f)
 {
     gdImagePtr im;
-    unsigned int width, height, x, y, *data, color;
+    unsigned int width, height, x, y, *data, color, alpha;
 
     width = cairo_image_surface_get_width(surface);
     height = cairo_image_surface_get_height(surface);
@@ -52,9 +52,12 @@ cairo_surface_write_to_gd(cairo_surface_t *surface, format_type format, FILE *f)
     for (y = 0; y < height; y++) {
         for (x = 0; x < width; x++) {
            color = *data++;
-           /* gd uses a transparency alpha instead of the more typical opacity */
            /* gd's max alpha is 127 */
-           color = (color & 0xffffff) | ((127 - (color >> 25)) << 24);
+           if ((alpha = (color >> 25) & 0x7f))
+               /* gd's alpha is transparency instead of opacity */
+               color = (color & 0xffffff) | ((127 - alpha) << 24);
+           else
+               color = im->transparent;
            gdImageSetPixel (im, x, y, color);
        }
     }