Generate GLSL in the CoglPipeline GLSL backend

The GLSL pipeline backend can now generate code to represent the
pipeline state in a similar way to the ARBfp backend. Most of the code
for this is taken from the GLES 2 wrapper.

clutter/cogl/cogl/cogl-context.c

@@ -132,6 +132,7 @@ cogl_create_context (void)
   _context->opaque_color_pipeline = cogl_pipeline_new ();
   _context->blended_color_pipeline = cogl_pipeline_new ();
   _context->texture_pipeline = cogl_pipeline_new ();
+  _context->fragment_header_buffer = g_string_new ("");
   _context->fragment_source_buffer = g_string_new ("");
   _context->source_stack = NULL;
 

clutter/cogl/cogl/cogl-context.h

@@ -86,6 +86,7 @@ typedef struct
   CoglPipeline     *opaque_color_pipeline; /* used for set_source_color */
   CoglPipeline     *blended_color_pipeline; /* used for set_source_color */
   CoglPipeline     *texture_pipeline; /* used for set_source_texture */
+  GString          *fragment_header_buffer;
   GString          *fragment_source_buffer;
   GList            *source_stack;
 

clutter/cogl/cogl/cogl-pipeline-glsl.c

@@ -29,8 +29,11 @@
 #include "config.h"
 #endif
 
+#include <string.h>
+
 #include "cogl-pipeline-private.h"
 #include "cogl-shader-private.h"
+#include "cogl-blend-string.h"
 
 #ifdef COGL_PIPELINE_BACKEND_GLSL
 
@@ -50,6 +53,15 @@
 #define glDeleteProgram      ctx->drv.pf_glDeleteProgram
 #define glGetProgramInfoLog  ctx->drv.pf_glGetProgramInfoLog
 #define glGetProgramiv       ctx->drv.pf_glGetProgramiv
+#define glCreateShader       ctx->drv.pf_glCreateShader
+#define glGetShaderiv        ctx->drv.pf_glGetShaderiv
+#define glGetShaderInfoLog   ctx->drv.pf_glGetShaderInfoLog
+#define glCompileShader      ctx->drv.pf_glCompileShader
+#define glShaderSource       ctx->drv.pf_glShaderSource
+#define glDeleteShader       ctx->drv.pf_glDeleteShader
+#define glGetUniformLocation ctx->drv.pf_glGetUniformLocation
+#define glUniform1i          ctx->drv.pf_glUniform1i
+#define glUniform4fv         ctx->drv.pf_glUniform4fv
 
 #endif /* HAVE_COGL_GLES2 */
 
@@ -63,6 +75,20 @@
 #include "../gles/cogl-gles2-wrapper.h"
 #endif
 
+/* This might not be defined on GLES */
+#ifndef GL_TEXTURE_3D
+#define GL_TEXTURE_3D                           0x806F
+#endif
+
+typedef struct _UnitState
+{
+  unsigned int sampled:1;
+  unsigned int combine_constant_used:1;
+  unsigned int dirty_combine_constant:1;
+
+  GLint combine_constant_uniform;
+} UnitState;
+
 typedef struct _GlslProgramState
 {
   int ref_count;
@@ -72,8 +98,9 @@ typedef struct _GlslProgramState
      program */
   unsigned int user_program_age;
   GLuint gl_program;
+  GString *header, *source;
+  UnitState *unit_state;
 
-#ifdef HAVE_COGL_GLES2
   /* To allow writing shaders that are portable between GLES 2 and
    * OpenGL Cogl prepends a number of boilerplate #defines and
    * declarations to user shaders. One of those declarations is an
@@ -82,11 +109,6 @@ typedef struct _GlslProgramState
    * attributes are in use.  The boilerplate also needs to be changed
    * if this increases. */
   int n_tex_coord_attribs;
-#endif
-
-  /* This is set to TRUE if the program has changed since we last
-     flushed the uniforms */
-  gboolean gl_program_changed;
 
 #ifdef HAVE_COGL_GLES2
   /* The GLES2 generated program that was generated from the user
@@ -96,6 +118,10 @@ typedef struct _GlslProgramState
      this GLSL backend starts generating its own shaders */
   GLuint gles2_program;
 #endif
+
+  /* We need to track the last pipeline that the program was used with
+   * so know if we need to update all of the uniforms */
+  CoglPipeline *last_used_for_pipeline;
 } GlslProgramState;
 
 typedef struct _CoglPipelineBackendGlslPrivate
@@ -117,6 +143,7 @@ glsl_program_state_new (int n_layers)
   GlslProgramState *state = g_slice_new0 (GlslProgramState);
 
   state->ref_count = 1;
+  state->unit_state = g_new0 (UnitState, n_layers);
 
   return state;
 }
@@ -158,23 +185,12 @@ glsl_program_state_unref (GlslProgramState *state)
           state->gl_program = 0;
         }
 
+      g_free (state->unit_state);
+
       g_slice_free (GlslProgramState, state);
     }
 }
 
-/* This tries to find the oldest ancestor whos state would generate
- * the same glsl program as the current pipeline. This is a simple
- * mechanism for reducing the number of glsl programs we have to
- * generate.
- */
-static CoglPipeline *
-find_glsl_authority (CoglPipeline *pipeline, CoglHandle user_program)
-{
-  /* Find the first pipeline that modifies the user shader */
-  return _cogl_pipeline_get_authority (pipeline,
-                                       COGL_PIPELINE_STATE_USER_SHADER);
-}
-
 static CoglPipelineBackendGlslPrivate *
 get_glsl_priv (CoglPipeline *pipeline)
 {
@@ -270,8 +286,8 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
   CoglPipeline *authority;
   CoglPipelineBackendGlslPrivate *authority_priv;
   CoglProgram *user_program;
-  GLuint gl_program;
   GSList *l;
+  int i;
 
   _COGL_GET_CONTEXT (ctx, FALSE);
 
@@ -279,9 +295,9 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
     return FALSE;
 
   user_program = cogl_pipeline_get_user_program (pipeline);
-  if (user_program == COGL_INVALID_HANDLE ||
+  if (user_program &&
       _cogl_program_get_language (user_program) != COGL_SHADER_LANGUAGE_GLSL)
-    return FALSE; /* XXX: change me when we support code generation here */
+    return FALSE;
 
   /* Now lookup our glsl backend private state (allocating if
    * necessary) */
@@ -302,12 +318,13 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
        * Also if the number of texture coordinate attributes in use has
        * increased, then delete the program so we can prepend a new
        * _cogl_tex_coord[] varying array declaration. */
-      if (priv->glsl_program_state->user_program_age == user_program->age
+      if (user_program == NULL ||
+          (priv->glsl_program_state->user_program_age == user_program->age
 #ifdef HAVE_COGL_GLES2
-          && priv->glsl_program_state->n_tex_coord_attribs >=
+           && (priv->glsl_program_state->n_tex_coord_attribs >=
-             n_tex_coord_attribs
+               n_tex_coord_attribs)
 #endif
-         )
+           ))
         return TRUE;
 
       /* Destroy the existing program. We can't just dirty the whole
@@ -326,7 +343,8 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
        * glsl-authority to maximize the chance that other pipelines can
        * share it.
        */
-      authority = find_glsl_authority (pipeline, user_program);
+      authority =
+        _cogl_pipeline_find_codegen_authority (pipeline, user_program);
       authority_priv = get_glsl_priv (authority);
       if (!authority_priv)
         {
@@ -342,6 +360,7 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
           GlslProgramState *glsl_program_state =
             glsl_program_state_new (n_layers);
           authority_priv->glsl_program_state = glsl_program_state;
+        }
 
       /* If the pipeline isn't actually its own glsl-authority
        * then take a reference to the program state associated
@@ -350,21 +369,17 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
         priv->glsl_program_state =
           glsl_program_state_ref (authority_priv->glsl_program_state);
     }
-    }
 
   /* If we make it here then we have a glsl_program_state struct
      without a gl_program either because this is the first time we've
      encountered it or because the user program has changed since it
      was last linked */
 
-  priv->glsl_program_state->gl_program_changed = TRUE;
-
-  GE_RET( gl_program, glCreateProgram () );
-
 #ifdef HAVE_COGL_GLES2
   /* Find the largest count of texture coordinate attributes
    * associated with each of the shaders so we can ensure a consistent
    * _cogl_tex_coord[] array declaration across all of the shaders.*/
+  if (user_program)
     for (l = user_program->attached_shaders; l; l = l->next)
       {
         CoglShader *shader = l->data;
@@ -373,40 +388,493 @@ _cogl_pipeline_backend_glsl_start (CoglPipeline *pipeline,
       }
 #endif
 
-  /* Add all of the shaders from the user program */
+  priv->glsl_program_state->n_tex_coord_attribs = n_tex_coord_attribs;
+
+  /* Check whether the user program contains a fragment
+     shader. Otherwise we need to generate one */
+  if (user_program)
     for (l = user_program->attached_shaders; l; l = l->next)
       {
         CoglShader *shader = l->data;
 
-      g_assert (shader->language == COGL_SHADER_LANGUAGE_GLSL);
+        if (shader->type == COGL_SHADER_TYPE_FRAGMENT)
-
+          goto no_fragment_shader_needed;
-      _cogl_shader_compile_real (shader, n_tex_coord_attribs);
-
-      GE( glAttachShader (gl_program, shader->gl_handle) );
       }
 
-  priv->glsl_program_state->gl_program = gl_program;
+  /* We reuse two grow-only GStrings for code-gen. One string
-  priv->glsl_program_state->user_program_age = user_program->age;
+     contains the uniform and attribute declarations while the
-#ifdef HAVE_COGL_GLES2
+     other contains the main function. We need two strings
-  priv->glsl_program_state->n_tex_coord_attribs = n_tex_coord_attribs;
+     because we need to dynamically declare attributes as the
-#endif
+     add_layer callback is invoked */
+  g_string_set_size (ctx->fragment_header_buffer, 0);
+  g_string_set_size (ctx->fragment_source_buffer, 0);
+  priv->glsl_program_state->header = ctx->fragment_header_buffer;
+  priv->glsl_program_state->source = ctx->fragment_source_buffer;
 
-  link_program (gl_program);
+  g_string_append (priv->glsl_program_state->source,
+                   "void\n"
+                   "main ()\n"
+                   "{\n");
+
+  for (i = 0; i < n_layers; i++)
+    {
+      priv->glsl_program_state->unit_state[i].sampled = FALSE;
+      priv->glsl_program_state->unit_state[i].combine_constant_used = FALSE;
+      priv->glsl_program_state->unit_state[i].dirty_combine_constant = FALSE;
+    }
+
+ no_fragment_shader_needed:
 
   return TRUE;
 }
 
-gboolean
+static void
+add_constant_lookup (GlslProgramState *glsl_program_state,
+                     CoglPipeline *pipeline,
+                     CoglPipelineLayer *layer,
+                     const char *swizzle)
+{
+  int unit_index = _cogl_pipeline_layer_get_unit_index (layer);
+
+  /* Create a sampler uniform for this layer if we haven't already */
+  if (!glsl_program_state->unit_state[unit_index].combine_constant_used)
+    {
+      g_string_append_printf (glsl_program_state->header,
+                              "uniform vec4 _cogl_layer_constant_%i;\n",
+                              unit_index);
+      glsl_program_state->unit_state[unit_index].combine_constant_used = TRUE;
+      glsl_program_state->unit_state[unit_index].dirty_combine_constant = TRUE;
+    }
+
+  g_string_append_printf (glsl_program_state->source,
+                          "_cogl_layer_constant_%i.%s",
+                          unit_index, swizzle);
+}
+
+static void
+add_texture_lookup (GlslProgramState *glsl_program_state,
+                    CoglPipeline *pipeline,
+                    CoglPipelineLayer *layer,
+                    const char *swizzle)
+{
+  CoglHandle texture;
+  int unit_index = _cogl_pipeline_layer_get_unit_index (layer);
+  const char *target_string, *tex_coord_swizzle;
+
+  texture = _cogl_pipeline_layer_get_texture (layer);
+
+  if (texture == COGL_INVALID_HANDLE)
+    {
+      target_string = "2D";
+      tex_coord_swizzle = "st";
+    }
+  else
+    {
+      GLenum gl_target;
+
+      cogl_texture_get_gl_texture (texture, NULL, &gl_target);
+      switch (gl_target)
+        {
+#ifndef HAVE_COGL_GLES2
+        case GL_TEXTURE_1D:
+          target_string = "1D";
+          tex_coord_swizzle = "s";
+          break;
+#endif
+
+        case GL_TEXTURE_2D:
+          target_string = "2D";
+          tex_coord_swizzle = "st";
+          break;
+
+#ifdef GL_ARB_texture_rectangle
+        case GL_TEXTURE_RECTANGLE_ARB:
+          target_string = "2DRect";
+          tex_coord_swizzle = "st";
+          break;
+#endif
+
+        case GL_TEXTURE_3D:
+          target_string = "3D";
+          tex_coord_swizzle = "stp";
+          break;
+
+        default:
+          g_assert_not_reached ();
+        }
+    }
+
+  /* Create a sampler uniform for this layer if we haven't already */
+  if (!glsl_program_state->unit_state[unit_index].sampled)
+    {
+      g_string_append_printf (glsl_program_state->header,
+                              "uniform sampler%s _cogl_sampler_%i;\n",
+                              target_string,
+                              unit_index);
+      glsl_program_state->unit_state[unit_index].sampled = TRUE;
+    }
+
+  g_string_append_printf (glsl_program_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 */
+  if (cogl_pipeline_get_layer_point_sprite_coords_enabled (pipeline,
+                                                           layer->index))
+    g_string_append_printf (glsl_program_state->source,
+                            "gl_PointCoord.%s",
+                            tex_coord_swizzle);
+  else
+    g_string_append_printf (glsl_program_state->source,
+                            "cogl_tex_coord_in[%d].%s",
+                            unit_index, tex_coord_swizzle);
+
+  g_string_append_printf (glsl_program_state->source, ").%s", swizzle);
+}
+
+typedef struct
+{
+  int unit_index;
+  CoglPipelineLayer *layer;
+} FindPipelineLayerData;
+
+static gboolean
+find_pipeline_layer_cb (CoglPipelineLayer *layer,
+                        void *user_data)
+{
+  FindPipelineLayerData *data = user_data;
+  int unit_index;
+
+  unit_index = _cogl_pipeline_layer_get_unit_index (layer);
+
+  if (unit_index == data->unit_index)
+    {
+      data->layer = layer;
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static void
+add_arg (GlslProgramState *glsl_program_state,
+         CoglPipeline *pipeline,
+         CoglPipelineLayer *layer,
+         GLint src,
+         GLenum operand,
+         const char *swizzle)
+{
+  GString *shader_source = glsl_program_state->source;
+  char alpha_swizzle[5] = "aaaa";
+
+  g_string_append_c (shader_source, '(');
+
+  if (operand == GL_ONE_MINUS_SRC_COLOR || operand == GL_ONE_MINUS_SRC_ALPHA)
+    g_string_append_printf (shader_source,
+                            "vec4(1.0, 1.0, 1.0, 1.0).%s - ",
+                            swizzle);
+
+  /* If the operand is reading from the alpha then replace the swizzle
+     with the same number of copies of the alpha */
+  if (operand == GL_SRC_ALPHA || operand == GL_ONE_MINUS_SRC_ALPHA)
+    {
+      alpha_swizzle[strlen (swizzle)] = '\0';
+      swizzle = alpha_swizzle;
+    }
+
+  switch (src)
+    {
+    case GL_TEXTURE:
+      add_texture_lookup (glsl_program_state,
+                          pipeline,
+                          layer,
+                          swizzle);
+      break;
+
+    case GL_CONSTANT:
+      add_constant_lookup (glsl_program_state,
+                           pipeline,
+                           layer,
+                           swizzle);
+      break;
+
+    case GL_PREVIOUS:
+      if (_cogl_pipeline_layer_get_unit_index (layer) > 0)
+        {
+          g_string_append_printf (shader_source, "cogl_color_out.%s", swizzle);
+          break;
+        }
+      /* flow through */
+    case GL_PRIMARY_COLOR:
+      g_string_append_printf (shader_source, "cogl_color_in.%s", swizzle);
+      break;
+
+    default:
+      if (src >= GL_TEXTURE0 && src < GL_TEXTURE0 + 32)
+        {
+          FindPipelineLayerData data;
+
+          data.unit_index = src - GL_TEXTURE0;
+          data.layer = layer;
+
+          _cogl_pipeline_foreach_layer_internal (pipeline,
+                                                 find_pipeline_layer_cb,
+                                                 &data);
+
+          add_texture_lookup (glsl_program_state,
+                              pipeline,
+                              data.layer,
+                              swizzle);
+        }
+      break;
+    }
+
+  g_string_append_c (shader_source, ')');
+}
+
+static void
+append_masked_combine (CoglPipeline *pipeline,
+                       CoglPipelineLayer *layer,
+                       const char *swizzle,
+                       GLint function,
+                       GLint *src,
+                       GLint *op)
+{
+  GlslProgramState *glsl_program_state = get_glsl_program_state (pipeline);
+  GString *shader_source = glsl_program_state->source;
+
+  g_string_append_printf (glsl_program_state->source,
+                          "  cogl_color_out.%s = ", swizzle);
+
+  switch (function)
+    {
+    case GL_REPLACE:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      break;
+
+    case GL_MODULATE:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      g_string_append (shader_source, " * ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], swizzle);
+      break;
+
+    case GL_ADD:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      g_string_append (shader_source, " + ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], swizzle);
+      break;
+
+    case GL_ADD_SIGNED:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      g_string_append (shader_source, " + ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], swizzle);
+      g_string_append_printf (shader_source,
+                              " - vec4(0.5, 0.5, 0.5, 0.5).%s",
+                              swizzle);
+      break;
+
+    case GL_SUBTRACT:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      g_string_append (shader_source, " - ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], swizzle);
+      break;
+
+    case GL_INTERPOLATE:
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], swizzle);
+      g_string_append (shader_source, " * ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[2], op[2], swizzle);
+      g_string_append (shader_source, " + ");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], swizzle);
+      g_string_append_printf (shader_source,
+                              " * (vec4(1.0, 1.0, 1.0, 1.0).%s - ",
+                              swizzle);
+      add_arg (glsl_program_state, pipeline, layer,
+               src[2], op[2], swizzle);
+      g_string_append_c (shader_source, ')');
+      break;
+
+    case GL_DOT3_RGB:
+    case GL_DOT3_RGBA:
+      g_string_append (shader_source, "vec4(4 * ((");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], "r");
+      g_string_append (shader_source, " - 0.5) * (");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], "r");
+      g_string_append (shader_source, " - 0.5) + (");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], "g");
+      g_string_append (shader_source, " - 0.5) * (");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], "g");
+      g_string_append (shader_source, " - 0.5) + (");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[0], op[0], "b");
+      g_string_append (shader_source, " - 0.5) * (");
+      add_arg (glsl_program_state, pipeline, layer,
+               src[1], op[1], "b");
+      g_string_append_printf (shader_source, " - 0.5))).%s", swizzle);
+      break;
+    }
+
+  g_string_append_printf (shader_source, ";\n");
+}
+
+static gboolean
 _cogl_pipeline_backend_glsl_add_layer (CoglPipeline *pipeline,
                                         CoglPipelineLayer *layer,
                                         unsigned long layers_difference)
 {
+  GlslProgramState *glsl_program_state = get_glsl_program_state (pipeline);
+  CoglPipelineLayer *combine_authority =
+    _cogl_pipeline_layer_get_authority (layer,
+                                        COGL_PIPELINE_LAYER_STATE_COMBINE);
+  CoglPipelineLayerBigState *big_state = combine_authority->big_state;
+
+  if (!glsl_program_state->source)
+    return TRUE;
+
+  if (!_cogl_pipeline_need_texture_combine_separate (combine_authority) ||
+      /* GL_DOT3_RGBA Is a bit weird as a GL_COMBINE_RGB function
+       * since if you use it, it overrides your ALPHA function...
+       */
+      big_state->texture_combine_rgb_func == GL_DOT3_RGBA)
+    append_masked_combine (pipeline,
+                           layer,
+                           "rgba",
+                           big_state->texture_combine_rgb_func,
+                           big_state->texture_combine_rgb_src,
+                           big_state->texture_combine_rgb_op);
+  else
+    {
+      append_masked_combine (pipeline,
+                             layer,
+                             "rgb",
+                             big_state->texture_combine_rgb_func,
+                             big_state->texture_combine_rgb_src,
+                             big_state->texture_combine_rgb_op);
+      append_masked_combine (pipeline,
+                             layer,
+                             "a",
+                             big_state->texture_combine_alpha_func,
+                             big_state->texture_combine_alpha_src,
+                             big_state->texture_combine_alpha_op);
+    }
+
   return TRUE;
 }
 
 gboolean
 _cogl_pipeline_backend_glsl_passthrough (CoglPipeline *pipeline)
 {
+  GlslProgramState *glsl_program_state = get_glsl_program_state (pipeline);
+
+  if (!glsl_program_state->source)
+    return TRUE;
+
+  g_string_append (glsl_program_state->source,
+                   "  cogl_color_out = cogl_color_in;\n");
+
+  return TRUE;
+}
+
+typedef struct
+{
+  int unit;
+  GLuint gl_program;
+  gboolean update_all;
+  GlslProgramState *glsl_program_state;
+} UpdateUniformsState;
+
+static gboolean
+get_uniform_cb (CoglPipeline *pipeline,
+                int layer_index,
+                void *user_data)
+{
+  UpdateUniformsState *state = user_data;
+  GlslProgramState *glsl_program_state = state->glsl_program_state;
+  UnitState *unit_state = &glsl_program_state->unit_state[state->unit];
+  GLint uniform_location;
+
+  _COGL_GET_CONTEXT (ctx, FALSE);
+
+  if (unit_state->sampled)
+    {
+      /* We can reuse the source buffer to create the uniform name because
+         the program has now been linked */
+      g_string_set_size (ctx->fragment_source_buffer, 0);
+      g_string_append_printf (ctx->fragment_source_buffer,
+                              "_cogl_sampler_%i", state->unit);
+
+      GE_RET( uniform_location,
+              glGetUniformLocation (state->gl_program,
+                                    ctx->fragment_source_buffer->str) );
+
+      g_return_val_if_fail (uniform_location != -1, TRUE);
+
+      /* We can set the uniform immediately because the samplers are
+         the unit index not the texture object number so it will never
+         change. Unfortunately GL won't let us use a constant instead
+         of a uniform */
+      GE( glUniform1i (uniform_location, state->unit) );
+    }
+
+  if (unit_state->combine_constant_used)
+    {
+      g_string_set_size (ctx->fragment_source_buffer, 0);
+      g_string_append_printf (ctx->fragment_source_buffer,
+                              "_cogl_layer_constant_%i", state->unit);
+
+      GE_RET( uniform_location,
+              glGetUniformLocation (state->gl_program,
+                                    ctx->fragment_source_buffer->str) );
+
+      g_return_val_if_fail (uniform_location != -1, TRUE);
+
+      unit_state->combine_constant_uniform = uniform_location;
+    }
+
+  state->unit++;
+
+  return TRUE;
+}
+
+static gboolean
+update_constants_cb (CoglPipeline *pipeline,
+                     int layer_index,
+                     void *user_data)
+{
+  UpdateUniformsState *state = user_data;
+  GlslProgramState *glsl_program_state = state->glsl_program_state;
+  UnitState *unit_state = &glsl_program_state->unit_state[state->unit++];
+
+  _COGL_GET_CONTEXT (ctx, FALSE);
+
+  if (unit_state->combine_constant_used &&
+      (state->update_all || unit_state->dirty_combine_constant))
+    {
+      float constant[4];
+      _cogl_pipeline_get_layer_combine_constant (pipeline,
+                                                 layer_index,
+                                                 constant);
+      GE (glUniform4fv (unit_state->combine_constant_uniform,
+                        1, constant));
+      unit_state->dirty_combine_constant = FALSE;
+    }
   return TRUE;
 }
 
@@ -415,11 +883,105 @@ _cogl_pipeline_backend_glsl_end (CoglPipeline *pipeline,
                                  unsigned long pipelines_difference)
 {
   GlslProgramState *glsl_program_state = get_glsl_program_state (pipeline);
+  CoglProgram *user_program;
   GLuint gl_program;
-  gboolean gl_program_changed;
+  gboolean gl_program_changed = FALSE;
+  UpdateUniformsState state;
+
+  _COGL_GET_CONTEXT (ctx, FALSE);
 
   gl_program = glsl_program_state->gl_program;
-  gl_program_changed = glsl_program_state->gl_program_changed;
+  user_program = cogl_pipeline_get_user_program (pipeline);
+
+  if (gl_program == 0)
+    {
+      gl_program_changed = TRUE;
+
+      GE_RET( gl_program, glCreateProgram () );
+
+      if (user_program)
+        {
+          GSList *l;
+
+          /* Add all of the shaders from the user program */
+          for (l = user_program->attached_shaders; l; l = l->next)
+            {
+              CoglShader *shader = l->data;
+
+              g_assert (shader->language == COGL_SHADER_LANGUAGE_GLSL);
+
+              _cogl_shader_compile_real (shader,
+                                         glsl_program_state->
+                                         n_tex_coord_attribs);
+
+              GE( glAttachShader (gl_program, shader->gl_handle) );
+            }
+
+          glsl_program_state->user_program_age = user_program->age;
+        }
+
+      if (glsl_program_state->source)
+        {
+          const GLchar *source_strings[2];
+          GLint lengths[2];
+          GLint compile_status;
+          GLuint shader;
+
+          COGL_STATIC_COUNTER (backend_glsl_compile_counter,
+                               "glsl compile counter",
+                               "Increments each time a new GLSL "
+                               "program is compiled",
+                               0 /* no application private data */);
+          COGL_COUNTER_INC (_cogl_uprof_context, backend_glsl_compile_counter);
+
+          g_string_append (glsl_program_state->source, "}\n");
+
+          if (G_UNLIKELY (cogl_debug_flags & COGL_DEBUG_SHOW_SOURCE))
+            g_message ("pipeline program:\n%s%s",
+                       glsl_program_state->header->str,
+                       glsl_program_state->source->str);
+
+          GE_RET( shader, glCreateShader (GL_FRAGMENT_SHADER) );
+
+          lengths[0] = glsl_program_state->header->len;
+          source_strings[0] = glsl_program_state->header->str;
+          lengths[1] = glsl_program_state->source->len;
+          source_strings[1] = glsl_program_state->source->str;
+
+          _cogl_shader_set_source_with_boilerplate (shader, GL_FRAGMENT_SHADER,
+                                                    glsl_program_state->
+                                                    n_tex_coord_attribs,
+                                                    2, /* count */
+                                                    source_strings, lengths);
+
+          GE( glCompileShader (shader) );
+          GE( glGetShaderiv (shader, GL_COMPILE_STATUS, &compile_status) );
+
+          if (!compile_status)
+            {
+              GLint len = 0;
+              char *shader_log;
+
+              GE( glGetShaderiv (shader, GL_INFO_LOG_LENGTH, &len) );
+              shader_log = g_alloca (len);
+              GE( glGetShaderInfoLog (shader, len, &len, shader_log) );
+              g_warning ("Shader compilation failed:\n%s", shader_log);
+            }
+
+          GE( glAttachShader (gl_program, shader) );
+
+          /* We can delete the shader now, but it won't actually be
+             destroyed until the program is also desroyed */
+          GE( glDeleteShader (shader) );
+
+          glsl_program_state->header = NULL;
+          glsl_program_state->source = NULL;
+        }
+
+      link_program (gl_program);
+
+      glsl_program_state->gl_program = gl_program;
+    }
 
 #ifdef HAVE_COGL_GLES2
   /* This function is a massive hack to get the GLES2 backend to
@@ -437,10 +999,31 @@ _cogl_pipeline_backend_glsl_end (CoglPipeline *pipeline,
   _cogl_use_program (gl_program, COGL_PIPELINE_PROGRAM_TYPE_GLSL);
 #endif
 
-  _cogl_program_flush_uniforms (cogl_pipeline_get_user_program (pipeline),
+  state.unit = 0;
-                                gl_program, gl_program_changed);
+  state.gl_program = gl_program;
+  state.glsl_program_state = glsl_program_state;
 
-  glsl_program_state->gl_program_changed = FALSE;
+  if (gl_program_changed)
+    cogl_pipeline_foreach_layer (pipeline,
+                                 get_uniform_cb,
+                                 &state);
+
+  state.unit = 0;
+  state.update_all = (gl_program_changed ||
+                      glsl_program_state->last_used_for_pipeline != pipeline);
+
+  cogl_pipeline_foreach_layer (pipeline,
+                               update_constants_cb,
+                               &state);
+
+  if (user_program)
+    _cogl_program_flush_uniforms (user_program,
+                                  gl_program,
+                                  gl_program_changed);
+
+  /* We need to track the last pipeline that the program was used with
+   * so know if we need to update all of the uniforms */
+  glsl_program_state->last_used_for_pipeline = pipeline;
 
   return TRUE;
 }
@@ -450,15 +1033,60 @@ _cogl_pipeline_backend_glsl_pre_change_notify (CoglPipeline *pipeline,
                                                CoglPipelineState change,
                                                const CoglColor *new_color)
 {
-  static const unsigned long glsl_op_changes =
+  static const unsigned long fragment_op_changes =
+    COGL_PIPELINE_STATE_LAYERS |
     COGL_PIPELINE_STATE_USER_SHADER;
+    /* TODO: COGL_PIPELINE_STATE_FOG */
 
-  if (!(change & glsl_op_changes))
+  if (!(change & fragment_op_changes))
     return;
 
   dirty_glsl_program_state (pipeline);
 }
 
+/* NB: layers are considered immutable once they have any dependants
+ * so although multiple pipelines can end up depending on a single
+ * static layer, we can guarantee that if a layer is being *changed*
+ * then it can only have one pipeline depending on it.
+ *
+ * XXX: Don't forget this is *pre* change, we can't read the new value
+ * yet!
+ */
+static void
+_cogl_pipeline_backend_glsl_layer_pre_change_notify (
+                                                CoglPipeline *owner,
+                                                CoglPipelineLayer *layer,
+                                                CoglPipelineLayerState change)
+{
+  CoglPipelineBackendGlslPrivate *priv;
+  static const unsigned long not_fragment_op_changes =
+    COGL_PIPELINE_LAYER_STATE_COMBINE_CONSTANT |
+    COGL_PIPELINE_LAYER_STATE_TEXTURE;
+
+  priv = get_glsl_priv (owner);
+  if (!priv)
+    return;
+
+  if (!(change & not_fragment_op_changes))
+    {
+      dirty_glsl_program_state (owner);
+      return;
+    }
+
+  if (change & COGL_PIPELINE_LAYER_STATE_COMBINE_CONSTANT)
+    {
+      GlslProgramState *glsl_program_state =
+        get_glsl_program_state (owner);
+      int unit_index = _cogl_pipeline_layer_get_unit_index (layer);
+      glsl_program_state->unit_state[unit_index].dirty_combine_constant = TRUE;
+    }
+
+  /* TODO: we could be saving snippets of texture combine code along
+   * with each layer and then when a layer changes we would just free
+   * the snippet. */
+  return;
+}
+
 static void
 _cogl_pipeline_backend_glsl_free_priv (CoglPipeline *pipeline)
 {
@@ -481,7 +1109,7 @@ const CoglPipelineBackend _cogl_pipeline_glsl_backend =
   _cogl_pipeline_backend_glsl_end,
   _cogl_pipeline_backend_glsl_pre_change_notify,
   NULL, /* pipeline_set_parent_notify */
-  NULL, /* layer_pre_change_notify */
+  _cogl_pipeline_backend_glsl_layer_pre_change_notify,
   _cogl_pipeline_backend_glsl_free_priv,
   NULL /* free_layer_priv */
 };