libgui|Drawable: Adding buffers with automatically generated identifiers

doomsday/libgui/include/de/gui/drawable.h

@@ -129,6 +129,17 @@ class LIBGUI_PUBLIC Drawable : public AssetGroup
      */
     void addBuffer(Id id, GLBuffer *buffer);
 
+    /**
+     * Adds a new buffer, reserving an unused identifier for it. The chosen
+     * identifier is larger than any of the buffer identifiers currently in
+     * use.
+     *
+     * @param buffer  GL buffer. Drawable gets ownership.
+     *
+     * @return  Identifier chosen for the buffer.
+     */
+    Id addBuffer(GLBuffer *buffer);
+
     /**
      * Creates a program or replaces an existing one with a blank program.
      * @param id  Identifier of the program. Cannot be zero.

doomsday/libgui/src/drawable.cpp

@@ -65,6 +65,16 @@ DENG2_PIMPL(Drawable)
         configs.clear();
     }
 
+    Id nextBufferId() const
+    {
+        Id next = 1;
+        foreach(Id id, buffers.keys())
+        {
+            next = de::max(id + 1, next);
+        }
+        return next;
+    }
+
     void replaceProgram(GLProgram const *src, GLProgram const *dest)
     {
         DENG2_FOR_EACH(BufferConfigs, i, configs)
@@ -154,6 +164,13 @@ void Drawable::addBuffer(Id id, GLBuffer *buffer)
     insert(*buffer, Required);
 }
 
+Drawable::Id Drawable::addBuffer(GLBuffer *buffer)
+{
+    Id id = d->nextBufferId();
+    addBuffer(id, buffer);
+    return id;
+}
+
 GLProgram &Drawable::addProgram(Id id)
 {
     // Program 0 is the default program.