[cogl] cogl-pipeline-opengl: Don't use number of tex units on fixed-function

[Neil Roberts <nroberts src gnome org>]

commit d8df30cb9cf818bba9c6f65090fc6722c3ddc418
Author: Neil Roberts <neil linux intel com>
Date:   Tue May 24 13:23:13 2011 +0100

    cogl-pipeline-opengl: Don't use number of tex units on fixed-function
    
    The CoglPipeline code uses a combination of GL_MAX_TEXTURE_COORDS,
    GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS and GL_MAX_TEXTURE_UNITS to
    determine the maximum number of layers to allow in a pipeline. However
    on fixed function hardware that doesn't advertise either GLSL or ARBfp
    it was still using the first two enums which will probably just return
    0 and set a GLerror. This meant that we effectively didn't support
    using any layers on purely fixed function hardware. This patch changes
    it to only use those two enums if the appropriate extensions are
    advertised and to always use GL_MAX_TEXTURE_UNITS except on GLES2
    where there is no fixed function.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=650966

 cogl/cogl-pipeline-opengl.c |   69 +++++++++++++++++++++++++++++++------------
 1 files changed, 50 insertions(+), 19 deletions(-)
---
diff --git a/cogl/cogl-pipeline-opengl.c b/cogl/cogl-pipeline-opengl.c
index 5019125..d91c706 100644
--- a/cogl/cogl-pipeline-opengl.c
+++ b/cogl/cogl-pipeline-opengl.c
@@ -646,28 +646,59 @@ get_max_activateable_texture_units (void)
 
   if (G_UNLIKELY (ctx->max_activateable_texture_units == -1))
     {
-#if defined (HAVE_COGL_GL)
-      GLint max_tex_coords;
-      GLint max_combined_tex_units;
-      GE (glGetIntegerv (GL_MAX_TEXTURE_COORDS, &max_tex_coords));
-      GE (glGetIntegerv (GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
-                         &max_combined_tex_units));
-      ctx->max_activateable_texture_units =
-        MAX (max_tex_coords - 1, max_combined_tex_units);
-#elif defined (HAVE_COGL_GLES2)
-      GLint max_vertex_attribs;
-      GLint max_combined_tex_units;
-      GE (glGetIntegerv (GL_MAX_VERTEX_ATTRIBS, &max_vertex_attribs));
-      GE (glGetIntegerv (GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
-                         &max_combined_tex_units));
+      GLint values[3];
+      int n_values = 0;
+      int i;
+
+#ifdef HAVE_COGL_GL
+      /* GL_MAX_TEXTURE_COORDS is provided for both GLSL and ARBfp. It
+         defines the number of texture coordinates that can be
+         uploaded (but doesn't necessarily relate to how many texture
+         images can be sampled) */
+      if (cogl_features_available (COGL_FEATURE_SHADERS_GLSL) ||
+          cogl_features_available (COGL_FEATURE_SHADERS_ARBFP))
+        /* Previously this code subtracted the value by one but there
+           was no explanation for why it did this and it doesn't seem
+           to make sense so it has been removed */
+        GE (glGetIntegerv (GL_MAX_TEXTURE_COORDS, values + n_values++));
+
+      /* GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS is defined for GLSL but
+         not ARBfp */
+      if (cogl_features_available (COGL_FEATURE_SHADERS_GLSL))
+        GE (glGetIntegerv (GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
+                           values + n_values++));
+#endif /* HAVE_COGL_GL */
+
+#ifdef HAVE_COGL_GLES2
+
+      GE (glGetIntegerv (GL_MAX_VERTEX_ATTRIBS, values + n_values));
       /* Two of the vertex attribs need to be used for the position
          and color */
-      ctx->max_activateable_texture_units =
-        MAX (max_vertex_attribs - 2, max_combined_tex_units);
-#else
+      values[n_values++] -= 2;
+
+      GE (glGetIntegerv (GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
+                         values + n_values++));
+
+#else /* HAVE_COGL_GLES2 */
+
+      /* GL_MAX_TEXTURE_UNITS defines the number of units that are
+         usable from the fixed function pipeline, therefore it isn't
+         available in GLES2. These are also tied to the number of
+         texture coordinates that can be uploaded so it should be less
+         than that available from the shader extensions */
       GE (glGetIntegerv (GL_MAX_TEXTURE_UNITS,
-                         &ctx->max_activateable_texture_units));
-#endif
+                         values + n_values++));
+
+#endif /* HAVE_COGL_GLES2 */
+
+      g_assert (n_values <= G_N_ELEMENTS (values) &&
+                n_values > 0);
+
+      /* Use the maximum value */
+      ctx->max_activateable_texture_units = values[0];
+      for (i = 1; i < n_values; i++)
+        ctx->max_activateable_texture_units =
+          MAX (values[i], ctx->max_activateable_texture_units);
     }
 
   return ctx->max_activateable_texture_units;