libgui|GL: TextureBank can use multiple atlases

Based on user-provided atlas IDs, the allocations in a TextureBank
can be split to multiple atlases.

ModelDrawable was updated to support separate atlases for different
texture map types.

doomsday/libs/gui/include/de/graphics/modeldrawable.h

@@ -473,12 +473,22 @@ class LIBGUI_PUBLIC ModelDrawable : public AssetGroup
     void setAtlas(IAtlas &atlas);
 
     /**
-     * Removes the model's atlas. All allocations this model has made from the atlas
+     * Sets the atlas to use for a specific type of textures. THis is needed for glInit(). Unlike
+     * setAtlas(atlas) that uses the same atlas for everything, this will associate a certain type
+     * of texture with a specific atlas.
+     *
+     * @param textureMap  Texture map. This
+     * @param atlas       Atlas for model textures of type @a textureMap.
+     */
+    void setAtlas(TextureMap textureMap, IAtlas &atlas);
+
+    /**
+     * Removes the model's atlases. All allocations this model has made from the atlas
      * are freed.
      */
     void unsetAtlas();
 
-    IAtlas *atlas() const;
+    IAtlas *atlas(TextureMap textureMap = Unknown) const;
 
     /**
      * Sets which textures are to be passed to the model shader via the GL buffer.

doomsday/libs/gui/include/de/graphics/texturebank.h

@@ -25,7 +25,7 @@
 namespace de {
 
 /**
- * Bank that stores images on an atlas.
+ * Bank that stores images on one or more atlases.
  *
  * The data item sources in the bank must be derived from TextureBank::ImageSource.
  *
@@ -34,6 +34,8 @@ namespace de {
 class LIBGUI_PUBLIC TextureBank : public Bank
 {
 public:
+    using AtlasId = int;
+
     /**
      * Base classs for entries in the bank. When requested, provides the Image data
      * of the specified item.
@@ -42,6 +44,9 @@ class LIBGUI_PUBLIC TextureBank : public Bank
     {
     public:
         ImageSource(DotPath const &sourcePath = "");
+        ImageSource(AtlasId atlasId, DotPath const &sourcePath);
+
+        AtlasId atlasId() const;
         DotPath const &sourcePath() const;
 
         virtual Image load() const = 0;
@@ -50,6 +55,14 @@ class LIBGUI_PUBLIC TextureBank : public Bank
         DENG2_PRIVATE(d)
     };
 
+    struct LIBGUI_PUBLIC Allocation
+    {
+        Id id;
+        AtlasId atlas;
+
+        operator Id const &() const { return id; }
+    };
+
 public:
     TextureBank(char const *nameForLog = "TextureBank",
                 Flags const &flags = DefaultFlags);
@@ -61,9 +74,18 @@ class LIBGUI_PUBLIC TextureBank : public Bank
      */
     void setAtlas(IAtlas *atlas);
 
-    IAtlas *atlas();
+    /**
+     * Sets one of the atlases that will be used for allocating images.
+     *
+     * @param atlasId  Id of the atlas.
+     *
+     * @param atlas Texture atlas.
+     */
+    void setAtlas(AtlasId atlasId, IAtlas *atlas);
+
+    IAtlas *atlas(AtlasId atlasId = 0);
 
-    Id const &texture(DotPath const &id);
+    Allocation texture(DotPath const &id);
 
     /**
      * Returns the source path of an image that has been loaded into the atlas.