fragend-glsl: Don't generate the default texture lookup if replaced

Previously the function containing the default texture lookup is
always generated regardless of whether there is a snippet with a
replace string which would cause it not be used. Now this snippets are
all scanned to check for replace strings before generating the texture
lookup.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

cogl/cogl-pipeline-fragend-glsl.c

@@ -37,6 +37,7 @@
 #include "cogl-pipeline-layer-private.h"
 #include "cogl-shader-private.h"
 #include "cogl-blend-string.h"
+#include "cogl-snippet-private.h"
 
 #ifdef COGL_PIPELINE_FRAGEND_GLSL
 
@@ -200,6 +201,19 @@ get_layer_fragment_snippets (CoglPipelineLayer *layer)
   return &layer->big_state->fragment_snippets;
 }
 
+static gboolean
+has_replace_hook (CoglPipelineLayer *layer,
+                  CoglSnippetHook hook)
+{
+  CoglPipelineSnippet *snippet;
+
+  COGL_LIST_FOREACH (snippet, get_layer_fragment_snippets (layer), list_node)
+    if (snippet->snippet->hook == hook && snippet->snippet->replace)
+      return TRUE;
+
+  return FALSE;
+}
+
 static gboolean
 _cogl_pipeline_fragend_glsl_start (CoglPipeline *pipeline,
                                    int n_layers,
@@ -374,9 +388,7 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
                                  CoglPipeline *pipeline,
                                  CoglPipelineLayer *layer)
 {
-  CoglHandle texture;
   int unit_index = _cogl_pipeline_layer_get_unit_index (layer);
-  const char *target_string, *tex_coord_swizzle;
   CoglPipelineSnippetData snippet_data;
 
   _COGL_GET_CONTEXT (ctx, NO_RETVAL);
@@ -415,7 +427,12 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
 
   g_string_append (shader_state->source, ");\n");
 
-  texture = _cogl_pipeline_layer_get_texture (layer);
+  /* There's no need to generate the real texture lookup if it's going
+     to be replaced */
+  if (!has_replace_hook (layer, COGL_SNIPPET_HOOK_TEXTURE_LOOKUP))
+    {
+      CoglHandle texture = _cogl_pipeline_layer_get_texture (layer);
+      const char *target_string, *tex_coord_swizzle;
 
       if (texture == NULL)
         {
@@ -481,6 +498,7 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
                                 target_string, unit_index, tex_coord_swizzle);
 
       g_string_append (shader_state->header, "}\n");
+    }
 
   /* Wrap the texture lookup in any snippets that have been hooked */
   memset (&snippet_data, 0, sizeof (snippet_data));

tests/conform/test-snippets.c

@@ -232,6 +232,20 @@ paint (TestState *state)
 
   cogl_object_unref (snippet);
 
+  /* Check replacing the texture lookup hook */
+  snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_TEXTURE_LOOKUP, NULL, NULL);
+  cogl_snippet_set_replace (snippet, "cogl_texel = vec4 (0.0, 0.0, 1.0, 0.0);");
+
+  pipeline = create_texture_pipeline ();
+  cogl_pipeline_add_layer_snippet (pipeline, 0, snippet);
+  cogl_push_source (pipeline);
+  cogl_rectangle_with_texture_coords (90, 0, 100, 10,
+                                      0, 0, 0, 0);
+  cogl_pop_source ();
+  cogl_object_unref (pipeline);
+
+  cogl_object_unref (snippet);
+
   /* Test replacing a previous snippet */
   pipeline = create_texture_pipeline ();
 
@@ -302,6 +316,7 @@ validate_result (void)
   test_utils_check_pixel (65, 5, 0x00ff00ff);
   test_utils_check_pixel (75, 5, 0x808000ff);
   test_utils_check_pixel (85, 5, 0x00ffffff);
+  test_utils_check_pixel (95, 5, 0x0000ffff);
   test_utils_check_pixel (105, 5, 0xff0000ff);
 }