OsmPath.java

package org.osmdroid.views.drawing;

import org.osmdroid.util.GeoPoint;
import org.osmdroid.views.Projection;

import android.graphics.Path;
import android.graphics.Point;

/**
 * Since the osmdroid canvas coordinate system is changing with every scroll, the x/y coordinates of
 * lat/long points is also always changing. Converting from lat/long to pixel values is a
 * potentially expensive operation and shouldn't be performed in the draw() cycle. Instead of
 * recalculating your {@link Path} points every draw cycle, you can use an OsmPath and call
 * {@link #onDrawCycle(Projection)} at the start of your draw call. This will simply shift the Path
 * the proper amount so that it is in the correct pixel position.
 * 
 * @author Marc Kurtz
 * 
 */
public class OsmPath extends Path {

	private final static GeoPoint sReferenceGeoPoint = new GeoPoint(0, 0);
	protected final Point mReferencePoint = new Point();
	private int mLastZoomLevel = -1;
	
    public OsmPath() {
		super();
	}

	public OsmPath(Path src) {
		super(src);
	}

	/**
	 * Call this method at the beginning of every draw() call.
	 */
	public void onDrawCycle(Projection proj) {
		if (mLastZoomLevel != proj.getZoomLevel()) {
			proj.toPixels(sReferenceGeoPoint, mReferencePoint);
			mLastZoomLevel = proj.getZoomLevel();
		}
		int x = mReferencePoint.x;
		int y = mReferencePoint.y;
		proj.toPixels(sReferenceGeoPoint, mReferencePoint);
		int deltaX = mReferencePoint.x - x;
		int deltaY = mReferencePoint.y - y;

		offset(deltaX, deltaY);
	}
}