pipeline: Add a snippet hook for the texture lookup

This adds a per-layer snippet hook for the texure lookup. Here the
snippet can modify the texture coordinates used for the lookup or
modify the texel resulting from the lookup. This is the first
per-layer hook so this also adds the
COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS state and all of the
boilerplate needed to make that work.

Most of the functions used by the pipeline state to manage the snippet
list has been moved into cogl-pipeline-snippet.c so that it can be
shared with the layer state.

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

11 files changed, 421 insertions, 149 deletions

diff --git a/cogl/cogl-pipeline-fragend-glsl.c b/cogl/cogl-pipeline-fragend-glsl.c
index 825e8fde..1a341359 100644
--- a/cogl/cogl-pipeline-fragend-glsl.c
+++ b/cogl/cogl-pipeline-fragend-glsl.c
@@ -191,6 +191,15 @@ get_fragment_snippets (CoglPipeline *pipeline)
   return &pipeline->big_state->fragment_snippets;
 }
 
+static CoglPipelineSnippetList *
+get_layer_fragment_snippets (CoglPipelineLayer *layer)
+{
+  unsigned long state = COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS;
+  layer = _cogl_pipeline_layer_get_authority (layer, state);
+
+  return &layer->big_state->fragment_snippets;
+}
+
 static gboolean
 _cogl_pipeline_fragend_glsl_start (CoglPipeline *pipeline,
                                    int n_layers,
@@ -368,6 +377,7 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
   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);
 
@@ -377,16 +387,29 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
   shader_state->unit_state[unit_index].sampled = TRUE;
 
   g_string_append_printf (shader_state->source,
-                          "  vec4 texel%i = ",
+                          "  vec4 texel%i = cogl_texture_lookup%i (",
+                          unit_index,
                           unit_index);
 
-  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_TEXTURING)))
-    {
-      g_string_append (shader_state->source,
-                       "vec4 (1.0, 1.0, 1.0, 1.0);\n");
+  /* If point sprite coord generation is being used then divert to the
+     built-in varying var for that instead of the texture
+     coordinates. We don't want to do this under GL because in that
+     case we will instead use glTexEnv(GL_COORD_REPLACE) to replace
+     the texture coords with the point sprite coords. Although GL also
+     supports the gl_PointCoord variable, it requires GLSL 1.2 which
+     would mean we would have to declare the GLSL version and check
+     for it */
+  if (ctx->driver == COGL_DRIVER_GLES2 &&
+      cogl_pipeline_get_layer_point_sprite_coords_enabled (pipeline,
+                                                           layer->index))
+    g_string_append_printf (shader_state->source,
+                            "gl_PointCoord");
+  else
+    g_string_append_printf (shader_state->source,
+                            "cogl_tex_coord_in[%d]",
+                            unit_index);
 
-      return;
-    }
+  g_string_append (shader_state->source, ");\n");
 
   texture = _cogl_pipeline_layer_get_texture (layer);
 
@@ -432,35 +455,50 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
     }
 
   /* Create a sampler uniform */
+  if (G_LIKELY (!COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_TEXTURING)))
+    g_string_append_printf (shader_state->header,
+                            "uniform sampler%s _cogl_sampler_%i;\n",
+                            target_string,
+                            unit_index);
+
   g_string_append_printf (shader_state->header,
-                          "uniform sampler%s _cogl_sampler_%i;\n",
-                          target_string,
+                          "vec4\n"
+                          "cogl_real_texture_lookup%i (vec4 coords)\n"
+                          "{\n"
+                          "  return ",
                           unit_index);
 
-  g_string_append_printf (shader_state->source,
-                          "texture%s (_cogl_sampler_%i, ",
-                          target_string, unit_index);
-
-  /* If point sprite coord generation is being used then divert to the
-     built-in varying var for that instead of the texture
-     coordinates. We don't want to do this under GL because in that
-     case we will instead use glTexEnv(GL_COORD_REPLACE) to replace
-     the texture coords with the point sprite coords. Although GL also
-     supports the gl_PointCoord variable, it requires GLSL 1.2 which
-     would mean we would have to declare the GLSL version and check
-     for it */
-  if (ctx->driver == COGL_DRIVER_GLES2 &&
-      cogl_pipeline_get_layer_point_sprite_coords_enabled (pipeline,
-                                                           layer->index))
-    g_string_append_printf (shader_state->source,
-                            "gl_PointCoord.%s",
-                            tex_coord_swizzle);
+  if (G_UNLIKELY (COGL_DEBUG_ENABLED (COGL_DEBUG_DISABLE_TEXTURING)))
+    g_string_append (shader_state->header,
+                     "vec4 (1.0, 1.0, 1.0, 1.0);\n");
   else
-    g_string_append_printf (shader_state->source,
-                            "cogl_tex_coord_in[%d].%s",
-                            unit_index, tex_coord_swizzle);
-
-  g_string_append (shader_state->source, ");\n");
+    g_string_append_printf (shader_state->header,
+                            "texture%s (_cogl_sampler_%i, coords.%s);\n",
+                            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));
+  snippet_data.snippets = get_layer_fragment_snippets (layer);
+  snippet_data.hook = COGL_PIPELINE_SNIPPET_HOOK_TEXTURE_LOOKUP;
+  snippet_data.chain_function = g_strdup_printf ("cogl_real_texture_lookup%i",
+                                                 unit_index);
+  snippet_data.final_name = g_strdup_printf ("cogl_texture_lookup%i",
+                                             unit_index);
+  snippet_data.function_prefix = g_strdup_printf ("cogl_texture_lookup_hook%i",
+                                                  unit_index);
+  snippet_data.return_type = "vec4";
+  snippet_data.return_variable = "cogl_texel";
+  snippet_data.arguments = "cogl_tex_coord";
+  snippet_data.argument_declarations = "vec4 cogl_tex_coord";
+  snippet_data.source_buf = shader_state->header;
+
+  _cogl_pipeline_snippet_generate_code (&snippet_data);
+
+  g_free ((char *) snippet_data.chain_function);
+  g_free ((char *) snippet_data.final_name);
+  g_free ((char *) snippet_data.function_prefix);
 }
 
 static void
diff --git a/cogl/cogl-pipeline-layer-private.h b/cogl/cogl-pipeline-layer-private.h
index 76fcf23b..e4285993 100644
--- a/cogl/cogl-pipeline-layer-private.h
+++ b/cogl/cogl-pipeline-layer-private.h
@@ -34,6 +34,7 @@
 #include "cogl-matrix.h"
 #include "cogl-pipeline-layer-state.h"
 #include "cogl-internal.h"
+#include "cogl-pipeline-snippet-private.h"
 
 #include <glib.h>
 
@@ -78,6 +79,7 @@ typedef enum
   COGL_PIPELINE_LAYER_STATE_COMBINE_CONSTANT_INDEX,
   COGL_PIPELINE_LAYER_STATE_USER_MATRIX_INDEX,
   COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS_INDEX,
+  COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS_INDEX,
 
   /* note: layers don't currently have any non-sparse state */
 
@@ -115,6 +117,9 @@ typedef enum
   COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS =
     1L<<COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS_INDEX,
 
+  COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS =
+    1L<<COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS_INDEX,
+
   /* COGL_PIPELINE_LAYER_STATE_TEXTURE_INTERN   = 1L<<8, */
 
 } CoglPipelineLayerState;
@@ -133,12 +138,14 @@ typedef enum
   (COGL_PIPELINE_LAYER_STATE_COMBINE | \
    COGL_PIPELINE_LAYER_STATE_COMBINE_CONSTANT | \
    COGL_PIPELINE_LAYER_STATE_USER_MATRIX | \
-   COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS)
+   COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS | \
+   COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS)
 
 #define COGL_PIPELINE_LAYER_STATE_MULTI_PROPERTY \
   (COGL_PIPELINE_LAYER_STATE_FILTERS | \
    COGL_PIPELINE_LAYER_STATE_WRAP_MODES | \
-   COGL_PIPELINE_LAYER_STATE_COMBINE)
+   COGL_PIPELINE_LAYER_STATE_COMBINE | \
+   COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS)
 
 #define COGL_PIPELINE_LAYER_STATE_AFFECTS_VERTEX_CODEGEN 0
 
@@ -193,6 +200,7 @@ typedef struct
 
   gboolean point_sprite_coords;
 
+  CoglPipelineSnippetList fragment_snippets;
 } CoglPipelineLayerBigState;
 
 struct _CoglPipelineLayer
diff --git a/cogl/cogl-pipeline-layer-state-private.h b/cogl/cogl-pipeline-layer-state-private.h
index b840fc94..a2831784 100644
--- a/cogl/cogl-pipeline-layer-state-private.h
+++ b/cogl/cogl-pipeline-layer-state-private.h
@@ -78,6 +78,10 @@ gboolean
 _cogl_pipeline_layer_point_sprite_coords_equal (CoglPipelineLayer *authority0,
                                                 CoglPipelineLayer *authority1);
 
+gboolean
+_cogl_pipeline_layer_fragment_snippets_equal (CoglPipelineLayer *authority0,
+                                              CoglPipelineLayer *authority1);
+
 void
 _cogl_pipeline_layer_hash_unit_state (CoglPipelineLayer *authority,
                                       CoglPipelineLayer **authorities,
@@ -123,4 +127,9 @@ _cogl_pipeline_layer_hash_point_sprite_state (CoglPipelineLayer *authority,
                                               CoglPipelineLayer **authorities,
                                               CoglPipelineHashState *state);
 
+void
+_cogl_pipeline_layer_hash_fragment_snippets_state (CoglPipelineLayer *authority,
+                                                   CoglPipelineLayer **authorities,
+                                                   CoglPipelineHashState *state);
+
 #endif /* __COGL_PIPELINE_LAYER_STATE_PRIVATE_H */
diff --git a/cogl/cogl-pipeline-layer-state.c b/cogl/cogl-pipeline-layer-state.c
index d0657639..8df86fca 100644
--- a/cogl/cogl-pipeline-layer-state.c
+++ b/cogl/cogl-pipeline-layer-state.c
@@ -774,6 +774,58 @@ cogl_pipeline_get_layer_point_sprite_coords_enabled (CoglPipeline *pipeline,
   return authority->big_state->point_sprite_coords;
 }
 
+static void
+_cogl_pipeline_layer_add_fragment_snippet (CoglPipeline *pipeline,
+                                           int layer_index,
+                                           CoglPipelineSnippetHook hook,
+                                           CoglSnippet *snippet)
+{
+  CoglPipelineLayerState change = COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS;
+  CoglPipelineLayer *layer, *authority;
+
+  _COGL_RETURN_IF_FAIL (cogl_is_pipeline (pipeline));
+
+  /* Note: this will ensure that the layer exists, creating one if it
+   * doesn't already.
+   *
+   * Note: If the layer already existed it's possibly owned by another
+   * pipeline. If the layer is created then it will be owned by
+   * pipeline. */
+  layer = _cogl_pipeline_get_layer (pipeline, layer_index);
+
+  /* Now find the ancestor of the layer that is the authority for the
+   * state we want to change */
+  authority = _cogl_pipeline_layer_get_authority (layer, change);
+
+  layer = _cogl_pipeline_layer_pre_change_notify (pipeline, layer, change);
+
+  _cogl_pipeline_snippet_list_add (&layer->big_state->fragment_snippets,
+                                   hook,
+                                   snippet);
+
+  /* If we weren't previously the authority on this state then we need
+   * to extended our differences mask and so it's possible that some
+   * of our ancestry will now become redundant, so we aim to reparent
+   * ourselves if that's true... */
+  if (layer != authority)
+    {
+      layer->differences |= change;
+      _cogl_pipeline_layer_prune_redundant_ancestry (layer);
+    }
+}
+
+void
+cogl_pipeline_add_texture_lookup_hook (CoglPipeline *pipeline,
+                                       int layer_index,
+                                       CoglSnippet *snippet)
+{
+  CoglPipelineSnippetHook hook = COGL_PIPELINE_SNIPPET_HOOK_TEXTURE_LOOKUP;
+  _cogl_pipeline_layer_add_fragment_snippet (pipeline,
+                                             layer_index,
+                                             hook,
+                                             snippet);
+}
+
 gboolean
 _cogl_pipeline_layer_texture_target_equal (CoglPipelineLayer *authority0,
                                            CoglPipelineLayer *authority1,
@@ -911,6 +963,16 @@ _cogl_pipeline_layer_point_sprite_coords_equal (CoglPipelineLayer *authority0,
   return big_state0->point_sprite_coords == big_state1->point_sprite_coords;
 }
 
+gboolean
+_cogl_pipeline_layer_fragment_snippets_equal (CoglPipelineLayer *authority0,
+                                              CoglPipelineLayer *authority1)
+{
+  return _cogl_pipeline_snippet_list_equal (&authority0->big_state->
+                                            fragment_snippets,
+                                            &authority1->big_state->
+                                            fragment_snippets);
+}
+
 static void
 setup_texture_combine_state (CoglBlendStringStatement *statement,
                              CoglPipelineCombineFunc *texture_combine_func,
@@ -1664,4 +1726,11 @@ _cogl_pipeline_layer_hash_point_sprite_state (CoglPipelineLayer *authority,
                                    sizeof (big_state->point_sprite_coords));
 }
 
-
+void
+_cogl_pipeline_layer_hash_fragment_snippets_state (CoglPipelineLayer *authority,
+                                                   CoglPipelineLayer **authorities,
+                                                   CoglPipelineHashState *state)
+{
+  _cogl_pipeline_snippet_list_hash (&authority->big_state->fragment_snippets,
+                                    &state->hash);
+}
diff --git a/cogl/cogl-pipeline-layer-state.h b/cogl/cogl-pipeline-layer-state.h
index b1f57367..7d6965b2 100644
--- a/cogl/cogl-pipeline-layer-state.h
+++ b/cogl/cogl-pipeline-layer-state.h
@@ -497,6 +497,47 @@ cogl_pipeline_set_layer_wrap_mode (CoglPipeline        *pipeline,
                                    int                  layer_index,
                                    CoglPipelineWrapMode mode);
 
+/**
+ * cogl_pipeline_add_texture_lookup_hook:
+ * @pipeline: A #CoglPipeline
+ * @layer: The layer whose texutre lookup should be hooked
+ * @snippet: The #CoglSnippet to add to the texture lookup for @layer
+ *
+ * Adds a shader snippet that will hook on to the texture lookup part
+ * of a given layer. This gives a chance for the application to modify
+ * the coordinates that will be used for the texture lookup or to
+ * alter the returned texel.
+ *
+ * Within the snippet code for this hook there are two extra variables
+ * available. ‘cogl_tex_coord’ is a vec4 which contains the texture
+ * coordinates that will be used for the texture lookup this can be
+ * modified. ‘cogl_texel’ will contain the result of the texture
+ * lookup. This can be modified.
+ *
+ * The ‘declarations’ string in @snippet will be inserted in the
+ * global scope of the shader. Use this to declare any uniforms,
+ * attributes or functions that the snippet requires.
+ *
+ * The ‘pre’ string in @snippet will be inserted at the top of the
+ * main() function before any fragment processing is done. This is a
+ * good place to modify the cogl_tex_coord variable.
+ *
+ * If a ‘replace’ string is given then this will be used instead of a
+ * the default texture lookup. The snippet would typically use its own
+ * sampler in this case.
+ *
+ * The ‘post’ string in @snippet will be inserted after texture lookup
+ * has been preformed. Here the snippet can modify the cogl_texel
+ * variable to alter the returned texel.
+ *
+ * Since: 1.10
+ * Stability: Unstable
+ */
+void
+cogl_pipeline_add_texture_lookup_hook (CoglPipeline *pipeline,
+                                       int layer_index,
+                                       CoglSnippet *snippet);
+
 #endif /* COGL_ENABLE_EXPERIMENTAL_API */
 
 G_END_DECLS
diff --git a/cogl/cogl-pipeline-layer.c b/cogl/cogl-pipeline-layer.c
index 0b5693fe..86e07508 100644
--- a/cogl/cogl-pipeline-layer.c
+++ b/cogl/cogl-pipeline-layer.c
@@ -204,6 +204,11 @@ _cogl_pipeline_layer_init_multi_property_sparse_state (
           }
         break;
       }
+    case COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS:
+      _cogl_pipeline_snippet_list_copy (&layer->big_state->fragment_snippets,
+                                        &authority->big_state->
+                                        fragment_snippets);
+      break;
     }
 }
 
@@ -579,6 +584,12 @@ _cogl_pipeline_layer_equal (CoglPipelineLayer *layer0,
                           _cogl_pipeline_layer_point_sprite_coords_equal))
     return FALSE;
 
+  if (layers_difference & COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS &&
+      !layer_state_equal (COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS_INDEX,
+                          authorities0, authorities1,
+                          _cogl_pipeline_layer_fragment_snippets_equal))
+    return FALSE;
+
   return TRUE;
 }
 
@@ -591,6 +602,9 @@ _cogl_pipeline_layer_free (CoglPipelineLayer *layer)
       layer->texture != NULL)
     cogl_object_unref (layer->texture);
 
+  if (layer->differences & COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS)
+    _cogl_pipeline_snippet_list_free (&layer->big_state->fragment_snippets);
+
   if (layer->differences & COGL_PIPELINE_LAYER_STATE_NEEDS_BIG_STATE)
     g_slice_free (CoglPipelineLayerBigState, layer->big_state);
 
diff --git a/cogl/cogl-pipeline-snippet-private.h b/cogl/cogl-pipeline-snippet-private.h
index 49fd6e55..0df49726 100644
--- a/cogl/cogl-pipeline-snippet-private.h
+++ b/cogl/cogl-pipeline-snippet-private.h
@@ -32,18 +32,12 @@
 #include "cogl-queue.h"
 
 /* Enumeration of all the hook points that a snippet can be attached
-   to within a pipeline. Note that although there are currently only
-   two points that directly correspond to the two state flags, the
-   idea isn't that each new enum here will mean a state flag. The
-   state flags are just intended to mark the split between hooks that
-   affect the fragment shader and hooks that affect the vertex
-   shader. For example, if we add a hook to wrap around the processing
-   for a particular layer then that hook would be part of the fragment
-   snippets state. */
+   to within a pipeline. */
 typedef enum
 {
   COGL_PIPELINE_SNIPPET_HOOK_VERTEX,
-  COGL_PIPELINE_SNIPPET_HOOK_FRAGMENT
+  COGL_PIPELINE_SNIPPET_HOOK_FRAGMENT,
+  COGL_PIPELINE_SNIPPET_HOOK_TEXTURE_LOOKUP
 } CoglPipelineSnippetHook;
 
 typedef struct _CoglPipelineSnippet CoglPipelineSnippet;
@@ -99,5 +93,25 @@ typedef struct
 void
 _cogl_pipeline_snippet_generate_code (const CoglPipelineSnippetData *data);
 
+void
+_cogl_pipeline_snippet_list_free (CoglPipelineSnippetList *list);
+
+void
+_cogl_pipeline_snippet_list_add (CoglPipelineSnippetList *list,
+                                 CoglPipelineSnippetHook hook,
+                                 CoglSnippet *snippet);
+
+void
+_cogl_pipeline_snippet_list_copy (CoglPipelineSnippetList *dst,
+                                  const CoglPipelineSnippetList *src);
+
+void
+_cogl_pipeline_snippet_list_hash (CoglPipelineSnippetList *list,
+                                  unsigned int *hash);
+
+gboolean
+_cogl_pipeline_snippet_list_equal (CoglPipelineSnippetList *list0,
+                                   CoglPipelineSnippetList *list1);
+
 #endif /* __COGL_PIPELINE_SNIPPET_PRIVATE_H */
 
diff --git a/cogl/cogl-pipeline-snippet.c b/cogl/cogl-pipeline-snippet.c
index b7a694c7..bb57abd6 100644
--- a/cogl/cogl-pipeline-snippet.c
+++ b/cogl/cogl-pipeline-snippet.c
@@ -32,6 +32,8 @@
 #include <string.h>
 
 #include "cogl-pipeline-snippet-private.h"
+#include "cogl-snippet-private.h"
+#include "cogl-util.h"
 
 /* Helper functions that are used by both GLSL pipeline backends */
 
@@ -158,3 +160,101 @@ _cogl_pipeline_snippet_generate_code (const CoglPipelineSnippetData *data)
                                 data->arguments ? data->arguments : "");
     }
 }
+
+static void
+_cogl_pipeline_snippet_free (CoglPipelineSnippet *pipeline_snippet)
+{
+  cogl_object_unref (pipeline_snippet->snippet);
+  g_slice_free (CoglPipelineSnippet, pipeline_snippet);
+}
+
+void
+_cogl_pipeline_snippet_list_free (CoglPipelineSnippetList *list)
+{
+  CoglPipelineSnippet *pipeline_snippet, *tmp;
+
+  COGL_LIST_FOREACH_SAFE (pipeline_snippet, list, list_node, tmp)
+    _cogl_pipeline_snippet_free (pipeline_snippet);
+}
+
+void
+_cogl_pipeline_snippet_list_add (CoglPipelineSnippetList *list,
+                                 CoglPipelineSnippetHook hook,
+                                 CoglSnippet *snippet)
+{
+  CoglPipelineSnippet *pipeline_snippet = g_slice_new (CoglPipelineSnippet);
+
+  pipeline_snippet->hook = hook;
+  pipeline_snippet->snippet = cogl_object_ref (snippet);
+
+  _cogl_snippet_make_immutable (pipeline_snippet->snippet);
+
+  if (COGL_LIST_EMPTY (list))
+    COGL_LIST_INSERT_HEAD (list, pipeline_snippet, list_node);
+  else
+    {
+      CoglPipelineSnippet *tail;
+
+      for (tail = COGL_LIST_FIRST (list);
+           COGL_LIST_NEXT (tail, list_node);
+           tail = COGL_LIST_NEXT (tail, list_node));
+
+      COGL_LIST_INSERT_AFTER (tail, pipeline_snippet, list_node);
+    }
+}
+
+void
+_cogl_pipeline_snippet_list_copy (CoglPipelineSnippetList *dst,
+                                  const CoglPipelineSnippetList *src)
+{
+  CoglPipelineSnippet *tail = NULL;
+  const CoglPipelineSnippet *l;
+
+  COGL_LIST_INIT (dst);
+
+  COGL_LIST_FOREACH (l, src, list_node)
+    {
+      CoglPipelineSnippet *copy = g_slice_dup (CoglPipelineSnippet, l);
+
+      cogl_object_ref (copy->snippet);
+
+      if (tail)
+        COGL_LIST_INSERT_AFTER (tail, copy, list_node);
+      else
+        COGL_LIST_INSERT_HEAD (dst, copy, list_node);
+
+      tail = copy;
+    }
+}
+
+void
+_cogl_pipeline_snippet_list_hash (CoglPipelineSnippetList *list,
+                                  unsigned int *hash)
+{
+  CoglPipelineSnippet *l;
+
+  COGL_LIST_FOREACH (l, list, list_node)
+    {
+      *hash = _cogl_util_one_at_a_time_hash (*hash,
+                                             &l->hook,
+                                             sizeof (CoglPipelineSnippetHook));
+      *hash = _cogl_util_one_at_a_time_hash (*hash,
+                                             &l->snippet,
+                                             sizeof (CoglSnippet *));
+    }
+}
+
+gboolean
+_cogl_pipeline_snippet_list_equal (CoglPipelineSnippetList *list0,
+                                   CoglPipelineSnippetList *list1)
+{
+  CoglPipelineSnippet *l0, *l1;
+
+  for (l0 = COGL_LIST_FIRST (list0), l1 = COGL_LIST_FIRST (list1);
+       l0 && l1;
+       l0 = COGL_LIST_NEXT (l0, list_node), l1 = COGL_LIST_NEXT (l1, list_node))
+    if (l0->hook != l1->hook || l0->snippet != l1->snippet)
+      return FALSE;
+
+  return l0 == NULL && l1 == NULL;
+}
diff --git a/cogl/cogl-pipeline-state.c b/cogl/cogl-pipeline-state.c
index 56cdb162..04caa918 100644
--- a/cogl/cogl-pipeline-state.c
+++ b/cogl/cogl-pipeline-state.c
@@ -340,21 +340,6 @@ _cogl_pipeline_uniforms_state_equal (CoglPipeline *authority0,
   return TRUE;
 }
 
-static gboolean
-_cogl_pipeline_snippet_list_equal (CoglPipelineSnippetList *list0,
-                                   CoglPipelineSnippetList *list1)
-{
-  CoglPipelineSnippet *l0, *l1;
-
-  for (l0 = COGL_LIST_FIRST (list0), l1 = COGL_LIST_FIRST (list1);
-       l0 && l1;
-       l0 = COGL_LIST_NEXT (l0, list_node), l1 = COGL_LIST_NEXT (l1, list_node))
-    if (l0->hook != l1->hook || l0->snippet != l1->snippet)
-      return FALSE;
-
-  return l0 == NULL && l1 == NULL;
-}
-
 gboolean
 _cogl_pipeline_vertex_snippets_state_equal (CoglPipeline *authority0,
                                             CoglPipeline *authority1)
@@ -1585,32 +1570,6 @@ cogl_pipeline_set_uniform_matrix (CoglPipeline *pipeline,
 }
 
 static void
-_cogl_pipeline_snippet_list_add (CoglPipelineSnippetList *list,
-                                 CoglPipelineSnippetHook hook,
-                                 CoglSnippet *snippet)
-{
-  CoglPipelineSnippet *pipeline_snippet = g_slice_new (CoglPipelineSnippet);
-
-  pipeline_snippet->hook = hook;
-  pipeline_snippet->snippet = cogl_object_ref (snippet);
-
-  _cogl_snippet_make_immutable (pipeline_snippet->snippet);
-
-  if (COGL_LIST_EMPTY (list))
-    COGL_LIST_INSERT_HEAD (list, pipeline_snippet, list_node);
-  else
-    {
-      CoglPipelineSnippet *tail;
-
-      for (tail = COGL_LIST_FIRST (list);
-           COGL_LIST_NEXT (tail, list_node);
-           tail = COGL_LIST_NEXT (tail, list_node));
-
-      COGL_LIST_INSERT_AFTER (tail, pipeline_snippet, list_node);
-    }
-}
-
-static void
 _cogl_pipeline_add_vertex_snippet (CoglPipeline *pipeline,
                                    CoglPipelineSnippetHook hook,
                                    CoglSnippet *snippet)
@@ -1682,14 +1641,40 @@ _cogl_pipeline_has_vertex_snippets (CoglPipeline *pipeline)
   return !COGL_LIST_EMPTY (&authority->big_state->vertex_snippets);
 }
 
+static gboolean
+check_layer_has_fragment_snippet (CoglPipelineLayer *layer,
+                                  void *user_data)
+{
+  unsigned long state = COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS;
+  CoglPipelineLayer *authority =
+    _cogl_pipeline_layer_get_authority (layer, state);
+  gboolean *found_fragment_snippet = user_data;
+
+  if (!COGL_LIST_EMPTY (&authority->big_state->fragment_snippets))
+    {
+      *found_fragment_snippet = TRUE;
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
 gboolean
 _cogl_pipeline_has_fragment_snippets (CoglPipeline *pipeline)
 {
   CoglPipeline *authority =
     _cogl_pipeline_get_authority (pipeline,
                                   COGL_PIPELINE_STATE_FRAGMENT_SNIPPETS);
+  gboolean found_fragment_snippet = FALSE;
 
-  return !COGL_LIST_EMPTY (&authority->big_state->fragment_snippets);
+  if (!COGL_LIST_EMPTY (&authority->big_state->fragment_snippets))
+    return TRUE;
+
+  _cogl_pipeline_foreach_layer_internal (pipeline,
+                                         check_layer_has_fragment_snippet,
+                                         &found_fragment_snippet);
+
+  return found_fragment_snippet;
 }
 
 void
@@ -1973,31 +1958,12 @@ _cogl_pipeline_compare_uniform_differences (unsigned long *differences,
     }
 }
 
-static void
-_cogl_pipeline_snippet_list_hash (CoglPipelineSnippetList *list,
-                                  CoglPipelineHashState *state)
-{
-  CoglPipelineSnippet *l;
-
-  COGL_LIST_FOREACH (l, list, list_node)
-    {
-      state->hash =
-        _cogl_util_one_at_a_time_hash (state->hash,
-                                       &l->hook,
-                                       sizeof (CoglPipelineSnippetHook));
-      state->hash =
-        _cogl_util_one_at_a_time_hash (state->hash,
-                                       &l->snippet,
-                                       sizeof (CoglSnippet *));
-    }
-}
-
 void
 _cogl_pipeline_hash_vertex_snippets_state (CoglPipeline *authority,
                                            CoglPipelineHashState *state)
 {
   _cogl_pipeline_snippet_list_hash (&authority->big_state->vertex_snippets,
-                                    state);
+                                    &state->hash);
 }
 
 void
@@ -2005,5 +1971,5 @@ _cogl_pipeline_hash_fragment_snippets_state (CoglPipeline *authority,
                                              CoglPipelineHashState *state)
 {
   _cogl_pipeline_snippet_list_hash (&authority->big_state->fragment_snippets,
-                                    state);
+                                    &state->hash);
 }
diff --git a/cogl/cogl-pipeline.c b/cogl/cogl-pipeline.c
index e47a5deb..2831b55f 100644
--- a/cogl/cogl-pipeline.c
+++ b/cogl/cogl-pipeline.c
@@ -445,22 +445,6 @@ destroy_weak_children_cb (CoglNode *node,
 }
 
 static void
-_cogl_pipeline_snippet_free (CoglPipelineSnippet *pipeline_snippet)
-{
-  cogl_object_unref (pipeline_snippet->snippet);
-  g_slice_free (CoglPipelineSnippet, pipeline_snippet);
-}
-
-static void
-_cogl_pipeline_snippet_list_free (CoglPipelineSnippetList *list)
-{
-  CoglPipelineSnippet *pipeline_snippet, *tmp;
-
-  COGL_LIST_FOREACH_SAFE (pipeline_snippet, list, list_node, tmp)
-    _cogl_pipeline_snippet_free (pipeline_snippet);
-}
-
-static void
 _cogl_pipeline_free (CoglPipeline *pipeline)
 {
   if (!pipeline->is_weak)
@@ -853,30 +837,6 @@ _cogl_pipeline_set_vertend (CoglPipeline *pipeline, int vertend)
 }
 
 static void
-_cogl_pipeline_snippet_list_copy (CoglPipelineSnippetList *dst,
-                                  const CoglPipelineSnippetList *src)
-{
-  CoglPipelineSnippet *tail = NULL;
-  const CoglPipelineSnippet *l;
-
-  COGL_LIST_INIT (dst);
-
-  COGL_LIST_FOREACH (l, src, list_node)
-    {
-      CoglPipelineSnippet *copy = g_slice_dup (CoglPipelineSnippet, l);
-
-      cogl_object_ref (copy->snippet);
-
-      if (tail)
-        COGL_LIST_INSERT_AFTER (tail, copy, list_node);
-      else
-        COGL_LIST_INSERT_HEAD (dst, copy, list_node);
-
-      tail = copy;
-    }
-}
-
-static void
 _cogl_pipeline_copy_differences (CoglPipeline *dest,
                                  CoglPipeline *src,
                                  unsigned long differences)
@@ -2642,9 +2602,12 @@ _cogl_pipeline_init_layer_state_hash_functions (void)
   _index = COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS_INDEX;
   layer_state_hash_functions[_index] =
     _cogl_pipeline_layer_hash_point_sprite_state;
+  _index = COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS_INDEX;
+  layer_state_hash_functions[_index] =
+    _cogl_pipeline_layer_hash_fragment_snippets_state;
 
   /* So we get a big error if we forget to update this code! */
-  g_assert (COGL_PIPELINE_LAYER_STATE_SPARSE_COUNT == 9);
+  g_assert (COGL_PIPELINE_LAYER_STATE_SPARSE_COUNT == 10);
 }
 
 static gboolean
@@ -2928,7 +2891,8 @@ _cogl_pipeline_get_layer_state_for_fragment_codegen (CoglContext *context)
     (COGL_PIPELINE_LAYER_STATE_COMBINE |
      COGL_PIPELINE_LAYER_STATE_TEXTURE_TARGET |
      COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS |
-     COGL_PIPELINE_LAYER_STATE_UNIT);
+     COGL_PIPELINE_LAYER_STATE_UNIT |
+     COGL_PIPELINE_LAYER_STATE_FRAGMENT_SNIPPETS);
 
   if (context->driver == COGL_DRIVER_GLES2)
     state |= COGL_PIPELINE_LAYER_STATE_POINT_SPRITE_COORDS;
diff --git a/tests/conform/test-snippets.c b/tests/conform/test-snippets.c
index f3e9ae11..2d96a992 100644
--- a/tests/conform/test-snippets.c
+++ b/tests/conform/test-snippets.c
@@ -9,6 +9,37 @@ typedef struct _TestState
   int stub;
 } TestState;
 
+static CoglPipeline *
+create_texture_pipeline (void)
+{
+  CoglPipeline *pipeline;
+  CoglHandle tex;
+  static const guint8 tex_data[] =
+    {
+      0xff, 0x00, 0x00, 0xff, /* red */  0x00, 0xff, 0x00, 0xff, /* green */
+      0x00, 0x00, 0xff, 0xff, /* blue */ 0xff, 0xff, 0x00, 0xff, /* yellow */
+    };
+
+  tex = cogl_texture_new_from_data (2, 2, /* width/height */
+                                    COGL_TEXTURE_NO_ATLAS,
+                                    COGL_PIXEL_FORMAT_RGBA_8888_PRE,
+                                    COGL_PIXEL_FORMAT_ANY,
+                                    8, /* rowstride */
+                                    tex_data);
+
+  pipeline = cogl_pipeline_new ();
+
+  cogl_pipeline_set_layer_texture (pipeline, 0, tex);
+
+  cogl_pipeline_set_layer_filters (pipeline, 0,
+                                   COGL_PIPELINE_FILTER_NEAREST,
+                                   COGL_PIPELINE_FILTER_NEAREST);
+
+  cogl_handle_unref (tex);
+
+  return pipeline;
+}
+
 static void
 paint (TestState *state)
 {
@@ -170,6 +201,23 @@ paint (TestState *state)
 
   cogl_object_unref (snippet);
 
+  /* Check the texture lookup hook */
+  snippet = cogl_snippet_new (NULL,
+                              "cogl_texel.b += 1.0;");
+  /* Flip the texture coordinates around the y axis so that it will
+     get the green texel */
+  cogl_snippet_set_pre (snippet, "cogl_tex_coord.x = 1.0 - cogl_tex_coord.x;");
+
+  pipeline = create_texture_pipeline ();
+  cogl_pipeline_add_texture_lookup_hook (pipeline, 0, snippet);
+  cogl_push_source (pipeline);
+  cogl_rectangle_with_texture_coords (80, 0, 90, 10,
+                                      0, 0, 0, 0);
+  cogl_pop_source ();
+  cogl_object_unref (pipeline);
+
+  cogl_object_unref (snippet);
+
   /* Sanity check modifying the snippet */
   snippet = cogl_snippet_new ("foo", "bar");
   g_assert_cmpstr (cogl_snippet_get_declarations (snippet), ==, "foo");
@@ -213,6 +261,7 @@ validate_result (void)
   test_utils_check_pixel (55, 5, 0x00ff00ff);
   test_utils_check_pixel (65, 5, 0x00ff00ff);
   test_utils_check_pixel (75, 5, 0x808000ff);
+  test_utils_check_pixel (85, 5, 0x00ffffff);
 }
 
 void