add RenderElement.getOffset()

vtm/src/org/oscim/renderer/elements/RenderElement.java

@@ -57,6 +57,14 @@ public abstract class RenderElement extends Inlist<RenderElement> {
 	/** compile vertex data to vbo. */
 	protected void compile(ShortBuffer sbuf) {
 
+	}
+
+	public int getOffset() {
+	    return offset;
+    }
+
+	public void setOffset(int offset) {
+	    this.offset = offset;
     }
 
 	/**