cogl-debug: Add an option to disable atlasing sharing

If COGL_DEBUG contains disable-shared-atlas Cogl will not try to share
the atlas between glyphs and images.

clutter/cogl/cogl/cogl-debug-options.h

@@ -112,6 +112,12 @@ OPT (DISABLE_ATLAS,
      "disable-atlas",
      "Disable texture atlasing",
      "Disable use of texture atlasing")
+OPT (DISABLE_SHARED_ATLAS,
+     "Root Cause",
+     "disable-shared-atlas",
+     "Disable sharing the texture atlas between text and images",
+     "When this is set the glyph cache will always use a separate texture "
+     "for its atlas. Otherwise it will try to share the atlas with images.")
 OPT (DISABLE_TEXTURING,
      "Root Cause",
      "disable-texturing",

clutter/cogl/cogl/cogl-debug.c

@@ -68,6 +68,7 @@ static const GDebugKey cogl_behavioural_debug_keys[] = {
   { "disable-software-transform", COGL_DEBUG_DISABLE_SOFTWARE_TRANSFORM },
   { "dump-atlas-image", COGL_DEBUG_DUMP_ATLAS_IMAGE },
   { "disable-atlas", COGL_DEBUG_DISABLE_ATLAS },
+  { "disable-shared-atlas", COGL_DEBUG_DISABLE_SHARED_ATLAS },
   { "disable-texturing", COGL_DEBUG_DISABLE_TEXTURING},
   { "disable-arbfp", COGL_DEBUG_DISABLE_ARBFP},
   { "disable-fixed", COGL_DEBUG_DISABLE_FIXED},

clutter/cogl/cogl/cogl-debug.h

@@ -49,6 +49,7 @@ typedef enum {
   COGL_DEBUG_ATLAS,
   COGL_DEBUG_DUMP_ATLAS_IMAGE,
   COGL_DEBUG_DISABLE_ATLAS,
+  COGL_DEBUG_DISABLE_SHARED_ATLAS,
   COGL_DEBUG_OPENGL,
   COGL_DEBUG_DISABLE_TEXTURING,
   COGL_DEBUG_DISABLE_ARBFP,

clutter/cogl/pango/cogl-pango-glyph-cache.c

@@ -204,6 +204,9 @@ cogl_pango_glyph_cache_add_to_global_atlas (CoglPangoGlyphCache *cache,
 {
   CoglHandle texture;
 
+  if (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_SHARED_ATLAS))
+    return FALSE;
+
   /* If the cache is using mipmapping then we can't use the global
      atlas because it would just get migrated back out */
   if (cache->use_mipmapping)