[cogl] Fix point sprite coordinates in shaders on GLES2

[Neil Roberts <nroberts src gnome org>]

commit cb3409b23caf324a548f82cfb88acc684cc71930
Author: Neil Roberts <neil linux intel com>
Date:   Mon Jul 2 14:23:10 2012 +0100

    Fix point sprite coordinates in shaders on GLES2
    
    When using the GLES2 driver with a pipeline layer that has point
    sprite coordinates enabled it extracts the texture coordinates from
    the gl_PointCoord builtin instead of cogl_tex_coord_in[*].
    gl_PointCoord is not quite the same as the regular texture coordinates
    because it is only a vec2 instead of a vec4. This used to work ok
    because either set of texture coordinates would always immediately be
    accessed using a swizzle of '.st' so it would effectively be converted
    to a vec2 anyway. However since the snippet hook for texture lookups
    was added the texture coordinates are now passed to a function to
    perform the actual lookup instead. This function always takes a vec4
    so the shader would not compile. This patch fixes it to construct a
    vec4 from gl_PointCoord by setting the third and fourth components to
    0.0 and 1.0.
    
    Reviewed-by: Robert Bragg <robert linux intel com>

 cogl/cogl-pipeline-fragend-glsl.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/cogl/cogl-pipeline-fragend-glsl.c b/cogl/cogl-pipeline-fragend-glsl.c
index c2c0370..d4e5a29 100644
--- a/cogl/cogl-pipeline-fragend-glsl.c
+++ b/cogl/cogl-pipeline-fragend-glsl.c
@@ -425,7 +425,7 @@ ensure_texture_lookup_generated (CoglPipelineShaderState *shader_state,
       cogl_pipeline_get_layer_point_sprite_coords_enabled (pipeline,
                                                            layer->index))
     g_string_append_printf (shader_state->source,
-                            "gl_PointCoord");
+                            "vec4 (gl_PointCoord, 0.0, 1.0)");
   else
     g_string_append_printf (shader_state->source,
                             "cogl_tex_coord_in[%d]",