[cogl] gl: bind position attribute to location 0

[Robert Bragg <rbragg src gnome org>]

commit 992ef7b3b49ebb56adde2133bb36330c04133a3f
Author: Robert Bragg <robert linux intel com>
Date:   Fri Aug 16 21:23:37 2013 +0100

    gl: bind position attribute to location 0
    
    Full GL treats the position attribute specially and requires that it
    must be bound to generic attribute location 0 unlike GLES 2.0 or
    GL 3.2 core. We now make sure to unconditionally bind the
    cogl_position_in attribute to location 0 before linking any glsl program
    in cogl.
    
    For reference the relevant part of the GL 3.0 spec that covers these
    semantics is Section 2.7 "Vertex Specification" pg 27
    
    After this change there was one remaining problem in
    test-custom-attributes where the test_short_verts() test was using its
    own "pos" attribute instead of cogl_position_in and so cogl wasn't able
    to ensure it would be bound to location 0.
    
    This updates the test to use cogl_position_in but to work around the
    fact that glVertexPointer doesn't support UNSIGNED_SHORT components we
    force the test to use the glsl backend by setting a shader snippet on
    the pipeline.
    
    https://bugs.freedesktop.org/show_bug.cgi?id=67548
    
    Reviewed-by: Neil Roberts <neil linux intel com>

 cogl/driver/gl/cogl-pipeline-progend-glsl.c |    7 ++++
 tests/conform/test-custom-attributes.c      |   45 +++++++++++++++-----------
 2 files changed, 33 insertions(+), 19 deletions(-)
---
diff --git a/cogl/driver/gl/cogl-pipeline-progend-glsl.c b/cogl/driver/gl/cogl-pipeline-progend-glsl.c
index 6051bb0..077cfd7 100644
--- a/cogl/driver/gl/cogl-pipeline-progend-glsl.c
+++ b/cogl/driver/gl/cogl-pipeline-progend-glsl.c
@@ -673,6 +673,13 @@ _cogl_pipeline_progend_glsl_end (CoglPipeline *pipeline,
       if ((backend_shader = _cogl_pipeline_vertend_glsl_get_shader (pipeline)))
         GE( ctx, glAttachShader (program_state->program, backend_shader) );
 
+      /* XXX: OpenGL as a special case requires the vertex position to
+       * be bound to generic attribute 0 so for simplicity we
+       * unconditionally bind the cogl_position_in attribute here...
+       */
+      GE( ctx, glBindAttribLocation (program_state->program,
+                                     0, "cogl_position_in"));
+
       link_program (program_state->program);
 
       program_changed = TRUE;
diff --git a/tests/conform/test-custom-attributes.c b/tests/conform/test-custom-attributes.c
index c27dfa1..633dc2a 100644
--- a/tests/conform/test-custom-attributes.c
+++ b/tests/conform/test-custom-attributes.c
@@ -24,6 +24,7 @@ typedef struct
 typedef struct
 {
   int16_t x, y;
+  int16_t r, g, b, a;
 } ShortVert;
 
 static void
@@ -167,7 +168,7 @@ test_byte_verts (TestState *state, int offset_x, int offset_y)
 static void
 test_short_verts (TestState *state, int offset_x, int offset_y)
 {
-  CoglAttribute *attributes[1];
+  CoglAttribute *attributes[2];
   CoglAttributeBuffer *buffer;
   CoglPipeline *pipeline, *pipeline2;
   CoglSnippet *snippet;
@@ -175,32 +176,31 @@ test_short_verts (TestState *state, int offset_x, int offset_y)
 
   static const ShortVert short_verts[] =
     {
-      { -10, -10 },
-      { -1, -10 },
-      { -5, -1 }
+      { -10, -10, /**/ 0xffff, 0, 0, 0xffff },
+      { -1, -10,  /**/ 0xffff, 0, 0, 0xffff },
+      { -5, -1, /**/ 0xffff, 0, 0, 0xffff }
     };
 
-  pipeline = cogl_pipeline_new (test_ctx);
-  snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_VERTEX_TRANSFORM,
-                              "attribute vec2 pos;",
-                              NULL);
-  cogl_snippet_set_replace (snippet,
-                            "cogl_position_out = "
-                            "cogl_modelview_projection_matrix * "
-                            "vec4 (pos, 0.0, 1.0);");
-  cogl_pipeline_add_snippet (pipeline, snippet);
-  cogl_object_unref (snippet);
+
+  pipeline = cogl_pipeline_copy (state->pipeline);
 
   cogl_pipeline_set_color4ub (pipeline, 255, 0, 0, 255);
 
   buffer = cogl_attribute_buffer_new (test_ctx,
                                       sizeof (short_verts), short_verts);
   attributes[0] = cogl_attribute_new (buffer,
-                                      "pos",
+                                      "cogl_position_in",
                                       sizeof (ShortVert),
                                       G_STRUCT_OFFSET (ShortVert, x),
                                       2, /* n_components */
                                       COGL_ATTRIBUTE_TYPE_SHORT);
+  attributes[1] = cogl_attribute_new (buffer,
+                                      "color",
+                                      sizeof (ShortVert),
+                                      G_STRUCT_OFFSET (ShortVert, r),
+                                      4, /* n_components */
+                                      COGL_ATTRIBUTE_TYPE_UNSIGNED_SHORT);
+  cogl_attribute_set_normalized (attributes[1], TRUE);
 
   cogl_framebuffer_push_matrix (test_fb);
   cogl_framebuffer_translate (test_fb,
@@ -211,7 +211,7 @@ test_short_verts (TestState *state, int offset_x, int offset_y)
   primitive = cogl_primitive_new_with_attributes (COGL_VERTICES_MODE_TRIANGLES,
                                                   3, /* n_vertices */
                                                   attributes,
-                                                  1); /* n_attributes */
+                                                  2); /* n_attributes */
   cogl_primitive_draw (primitive, test_fb, pipeline);
   cogl_object_unref (primitive);
 
@@ -221,14 +221,21 @@ test_short_verts (TestState *state, int offset_x, int offset_y)
 
   /* Test again treating the attribute as unsigned */
   attributes[0] = cogl_attribute_new (buffer,
-                                      "pos",
+                                      "cogl_position_in",
                                       sizeof (ShortVert),
                                       G_STRUCT_OFFSET (ShortVert, x),
                                       2, /* n_components */
                                       COGL_ATTRIBUTE_TYPE_UNSIGNED_SHORT);
 
-  pipeline2 = cogl_pipeline_copy (pipeline);
-  cogl_pipeline_set_color4ub (pipeline2, 0, 255, 0, 255);
+  /* XXX: this is a hack to force the pipeline to use the glsl backend
+   * because we know it's not possible to test short vertex position
+   * components with the legacy GL backend since which might otherwise
+   * be used internally... */
+  pipeline2 = cogl_pipeline_new (test_ctx);
+  snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_VERTEX,
+                              "attribute vec4 color;",
+                              "cogl_color_out = vec4 (0.0, 1.0, 0.0, 1.0);");
+  cogl_pipeline_add_snippet (pipeline2, snippet);
 
   cogl_framebuffer_push_matrix (test_fb);
   cogl_framebuffer_translate (test_fb,