[cogl] Add the cogl_point_coord snippet builtin

[Neil Roberts <nroberts src gnome org>]

commit c28fc054788e88627bcc2346f4c4c368870ff777
Author: Neil Roberts <neil linux intel com>
Date:   Sun Aug 25 02:19:05 2013 +0100

    Add the cogl_point_coord snippet builtin
    
    This adds a #define for gl_PointCoord to all shaders so that it can be
    accessed with a name in the Cogl namespace.
    
    Reviewed-by: Robert Bragg <robert linux intel com>

 cogl/cogl-glsl-shader-boilerplate.h         |    4 +++-
 cogl/cogl-snippet.h                         |   13 +++++++++++++
 cogl/driver/gl/cogl-pipeline-fragend-glsl.c |    2 +-
 3 files changed, 17 insertions(+), 2 deletions(-)
---
diff --git a/cogl/cogl-glsl-shader-boilerplate.h b/cogl/cogl-glsl-shader-boilerplate.h
index 99c1dbc..798149e 100644
--- a/cogl/cogl-glsl-shader-boilerplate.h
+++ b/cogl/cogl-glsl-shader-boilerplate.h
@@ -64,7 +64,9 @@
   "#define cogl_color_out gl_FragColor\n" \
   "#define cogl_depth_out gl_FragDepth\n" \
   "\n" \
-  "#define cogl_front_facing gl_FrontFacing\n"
+  "#define cogl_front_facing gl_FrontFacing\n" \
+  "\n" \
+  "#define cogl_point_coord gl_PointCoord\n"
 #if 0
   /* GLSL 1.2 has a bottom left origin, though later versions
    * allow use of an origin_upper_left keyword which would be
diff --git a/cogl/cogl-snippet.h b/cogl/cogl-snippet.h
index 5eecbfc..cdce3b2 100644
--- a/cogl/cogl-snippet.h
+++ b/cogl/cogl-snippet.h
@@ -271,6 +271,19 @@ COGL_BEGIN_DECLS
  *    coloring algorithms. This is equivalent to #gl_FrontFacing.
  *   </para></glossdef>
  *  </glossentry>
+ *  <glossentry>
+ *   <glossterm>vec2 <emphasis>cogl_point_coord</emphasis></glossterm>
+ *   <glossdef><para>
+ *    When rendering points, this will contain a vec2 which represents
+ *    the position within the point of the current fragment.
+ *    vec2(0.0,0.0) will be the topleft of the point and vec2(1.0,1.0)
+ *    will be the bottom right. Note that there is currently a bug in
+ *    Cogl where when rendering to an offscreen buffer these
+ *    coordinates will be upside-down. The value is undefined when not
+ *    rendering points. This builtin can only be used if the
+ *    %COGL_FEATURE_ID_POINT_SPRITE feature is available.
+ *   </para></glossdef>
+ *  </glossentry>
  * </glosslist>
  *
  * Here is an example of using a snippet to add a desaturate effect to the
diff --git a/cogl/driver/gl/cogl-pipeline-fragend-glsl.c b/cogl/driver/gl/cogl-pipeline-fragend-glsl.c
index 46264a9..aff4225 100644
--- a/cogl/driver/gl/cogl-pipeline-fragend-glsl.c
+++ b/cogl/driver/gl/cogl-pipeline-fragend-glsl.c
@@ -408,7 +408,7 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
   if (cogl_pipeline_get_layer_point_sprite_coords_enabled (pipeline,
                                                            layer->index))
     g_string_append_printf (shader_state->source,
-                            "vec4 (gl_PointCoord, 0.0, 1.0)");
+                            "vec4 (cogl_point_coord, 0.0, 1.0)");
   else
     g_string_append_printf (shader_state->source,
                             "cogl_tex_coord%i_in",