[Cogl] [PATCH] cogl-gst: Don't replace previous layers in default shader

[Neil Roberts]

Previously, when CoglGST generated the default sampling snippet it
would set the replace string so that Cogl wouldn't generate any
redundant code for the other layers. However this also meant that it
wouldn't modulate with the default colour. This patch changes it to
set the combine mode on all of the layers to REPLACE(PREVIOUS) so that
it just copies the previous layer without generating any texture
sampling. That way the fragment snippet for the final layer can just
modulate the previous value with the video sampling function. This
makes it possible to set a color on the pipeline and have it modulate
the video. Also if we eventually add a way to insert layers before the
GST sampling layer then it can modulate with those.
---
 cogl-gst/cogl-gst-shader.c     |  2 +-
 cogl-gst/cogl-gst-video-sink.c | 20 +++++++++++++-------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/cogl-gst/cogl-gst-shader.c b/cogl-gst/cogl-gst-shader.c
index bc11f18..0a81025 100644
--- a/cogl-gst/cogl-gst-shader.c
+++ b/cogl-gst/cogl-gst-shader.c
@@ -78,4 +78,4 @@ _cogl_gst_shader_ayuv_to_rgba_decl[] =
 
 const char
 _cogl_gst_shader_default_sample[] =
-  "  cogl_layer = cogl_gst_sample_video (cogl_tex_coord0_in.st);\n";
+  "  cogl_layer *= cogl_gst_sample_video (cogl_tex_coord0_in.st);\n";
diff --git a/cogl-gst/cogl-gst-video-sink.c b/cogl-gst/cogl-gst-video-sink.c
index 414cc06..231b828 100644
--- a/cogl-gst/cogl-gst-video-sink.c
+++ b/cogl-gst/cogl-gst-video-sink.c
@@ -226,6 +226,7 @@ create_template_pipeline (CoglGstVideoSink *sink,
   if (decl)
     {
       static CoglSnippet *default_sample_snippet = NULL;
+      int i;
 
       /* The global sampling function gets added to both the fragment
        * and vertex stages. The hope is that the GLSL compiler will
@@ -246,16 +247,21 @@ create_template_pipeline (CoglGstVideoSink *sink,
       cogl_pipeline_add_snippet (priv->pipeline,
                                  snippet_cache->fragment_snippet);
 
-      /* Set the replace string for the last layer so that no
-       * redundant code for the previous layers will be generated. The
-       * application can also replace this default sampling by adding
-       * another layer */
+      /* Set all of the layers to just directly copy from the previous
+       * layer so that it won't redundantly generate code to sample
+       * the intermediate textures */
+      for (i = 0; i < n_layers; i++)
+        cogl_pipeline_set_layer_combine (priv->pipeline,
+                                         i,
+                                         "RGBA=REPLACE(PREVIOUS)",
+                                         NULL);
+
       if (default_sample_snippet == NULL)
         {
           default_sample_snippet =
-            cogl_snippet_new (COGL_SNIPPET_HOOK_LAYER_FRAGMENT, NULL, NULL);
-          cogl_snippet_set_replace (default_sample_snippet,
-                                    _cogl_gst_shader_default_sample);
+            cogl_snippet_new (COGL_SNIPPET_HOOK_LAYER_FRAGMENT,
+                              NULL, /* declarations */
+                              _cogl_gst_shader_default_sample);
         }
       cogl_pipeline_add_layer_snippet (priv->pipeline,
                                        n_layers - 1,
-- 
1.7.11.3.g3c3efa5