BucketRenderer: add default implementation for update()

- handy for simple (debug) layers

vtm/src/org/oscim/renderer/BucketRenderer.java

@@ -43,7 +43,7 @@ import org.slf4j.LoggerFactory;
  * 
  * All methods that modify 'buckets' MUST be synchronized!
  */
-public abstract class BucketRenderer extends LayerRenderer {
+public class BucketRenderer extends LayerRenderer {
 
 	public static final Logger log = LoggerFactory.getLogger(BucketRenderer.class);
 
@@ -65,6 +65,21 @@ public abstract class BucketRenderer extends LayerRenderer {
 		mMapPosition = new MapPosition();
 	}
 
+	protected boolean mInititialzed;
+
+	/**
+	 * Default implementation:
+	 * Copy initial Viewport position and compile buckets.
+	 */
+	@Override
+	protected void update(GLViewport v) {
+		if (!mInititialzed) {
+			mMapPosition.copy(v.pos);
+			mInititialzed = true;
+			compile();
+		}
+	}
+
 	/**
 	 * Render all 'buckets'
 	 */