libgui|ModelDrawable: Normal and height maps

The vertex data handled my ModelDrawable now contains information for
specifying the normal map for the geometry. This can come from the
model file (if specified), or it can use a common default normal map
(e.g., simple +Z vector). Also, one can manually specify a custom file
as the normal map.

doomsday/libgui/include/de/graphics/modeldrawable.h

@@ -45,6 +45,13 @@ class LIBGUI_PUBLIC ModelDrawable : public AssetGroup
     /// An error occurred during the loading of the model data. @ingroup errors
     DENG2_ERROR(LoadError);
 
+    enum TextureMap
+    {
+        Diffuse,
+        Normals,
+        Height
+    };
+
     /**
      * Animation state for a model. There can be any number of ongoing animations,
      * targeting individual nodes of a model.
@@ -196,6 +203,32 @@ class LIBGUI_PUBLIC ModelDrawable : public AssetGroup
      */
     void unsetAtlas();
 
+    /**
+     * Sets the normal map that is used if no other normals are provided.
+     *
+     * @param atlasId  Identifier in the atlas.
+     */
+    void setDefaultNormals(Id const &atlasId);
+
+    /**
+     * Locates a material specified in the model by its name.
+     *
+     * @param name  Name of the material
+     *
+     * @return Material id.
+     */
+    int materialId(String const &name) const;
+
+    /**
+     * Sets or changes one of the texture maps used by the model. This can be used to
+     * override the maps set up automatically by glInit().
+     *
+     * @param materialId  Which material to modify.
+     * @param textureMap  Texture to set.
+     * @param path        Path of the texture image.
+     */
+    void setTexturePath(int materialId, TextureMap textureMap, String const &path);
+
     /**
      * Sets the GL program used for shading the model.
      *