material: Adds _get_layer_combine_constant API

This adds an internal _cogl_material_get_layer_combine_constant function
so we can query the current layer combine constant back. We should
probably make this a public property getter, but for now we just need
this so we can read the constant in the arbfp backend.

clutter/cogl/cogl/cogl-material-private.h

@@ -913,5 +913,10 @@ _cogl_material_foreach_layer (CoglMaterial *material,
 int
 _cogl_material_layer_get_unit_index (CoglMaterialLayer *layer);
 
+void
+_cogl_material_get_layer_combine_constant (CoglMaterial *material,
+                                           int layer_index,
+                                           float *constant);
+
 #endif /* __COGL_MATERIAL_PRIVATE_H */
 

clutter/cogl/cogl/cogl-material.c

@@ -4875,6 +4875,32 @@ changed:
   handle_automatic_blend_enable (material, COGL_MATERIAL_STATE_LAYERS);
 }
 
+void
+_cogl_material_get_layer_combine_constant (CoglMaterial *material,
+                                           int layer_index,
+                                           float *constant)
+{
+  CoglMaterialLayerState       change =
+    COGL_MATERIAL_LAYER_STATE_COMBINE_CONSTANT;
+  CoglMaterialLayer *layer;
+  CoglMaterialLayer *authority;
+
+  g_return_if_fail (cogl_is_material (material));
+
+  /* Note: this will ensure that the layer exists, creating one if it
+   * doesn't already.
+   *
+   * Note: If the layer already existed it's possibly owned by another
+   * material. If the layer is created then it will be owned by
+   * material. */
+  layer = _cogl_material_get_layer (material, layer_index);
+  /* FIXME: we shouldn't ever construct a layer in a getter function */
+
+  authority = _cogl_material_layer_get_authority (layer, change);
+  memcpy (constant, authority->big_state->texture_combine_constant,
+          sizeof (float) * 4);
+}
+
 void
 cogl_material_set_layer_matrix (CoglMaterial *material,
 				int layer_index,