pixman_image_set_alpha_map(): Disallow alpha map cycles

If someone tries to set an alpha map that itself has an alpha map,
simply return. Also, if someone tries to add an alpha map to an image
that is being _used_ as an alpha map, simply return.

This ensures that an alpha map can never have an alpha map.

diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
index 269c3c1..cdc9c40 100644 (file)
--- a/pixman/pixman-image.c
+++ b/pixman/pixman-image.c
@@ -101,6 +101,7 @@ _pixman_image_allocate (void)
 
        pixman_region32_init (&common->clip_region);
 
+       common->alpha_count = 0;
        common->have_clip_region = FALSE;
        common->clip_sources = FALSE;
        common->transform = NULL;
@@ -668,15 +669,41 @@ pixman_image_set_alpha_map (pixman_image_t *image,
 
     return_if_fail (!alpha_map || alpha_map->type == BITS);
 
+    if (alpha_map && common->alpha_count > 0)
+    {
+       /* If this image is being used as an alpha map itself,
+        * then you can't give it an alpha map of its own.
+        */
+       return;
+    }
+
+    if (alpha_map && alpha_map->common.alpha_map)
+    {
+       /* If the image has an alpha map of its own,
+        * then it can't be used as an alpha map itself
+        */
+       return;
+    }
+
     if (common->alpha_map != (bits_image_t *)alpha_map)
     {
        if (common->alpha_map)
+       {
+           common->alpha_map->common.alpha_count--;
+
            pixman_image_unref ((pixman_image_t *)common->alpha_map);
+       }
 
        if (alpha_map)
+       {
            common->alpha_map = (bits_image_t *)pixman_image_ref (alpha_map);
+
+           common->alpha_map->common.alpha_count++;
+       }
        else
+       {
            common->alpha_map = NULL;
+       }
     }
 
     common->alpha_origin_x = x;

diff --git a/pixman/pixman-private.h b/pixman/pixman-private.h
index 0629c42..c4e6bb8 100644 (file)
--- a/pixman/pixman-private.h
+++ b/pixman/pixman-private.h
@@ -80,6 +80,7 @@ struct image_common
     image_type_t                type;
     int32_t                     ref_count;
     pixman_region32_t           clip_region;
+    int32_t                    alpha_count;        /* How many times this image is being used as an alpha map */
     pixman_bool_t               have_clip_region;   /* FALSE if there is no clip */
     pixman_bool_t               client_clip;        /* Whether the source clip was
                                                       set by a client */