Question

I want to draw arrows manually over map. I’m not using the rotation of drawables for performance issues as I have many overlays that slow the app if drawn using this technique.

I will draw arrows manually, given a gps point and rotation angle I need to draw the arrow over that point.
I will extend overlay class and on the draw method, I will do the drawing work.

Any suggestions ?

Answer 1

I dealt with the same problem in my app. The code is on github

Basically I override draw and rotate the canvas before drawing the arrow.

@Override
public void draw(Canvas canvas) {

    //NOTE: 0, 0 is the bottom center point of the bus icon

    //first draw the bus
    vehicle.draw(canvas);

    //then draw arrow
    if (arrow != null && heading != BusLocation.NO_HEADING)
    {
        //put the arrow in the bus window

        int arrowLeft = -(arrow.getIntrinsicWidth() / 4);
        int arrowTop = -vehicle.getIntrinsicHeight() + arrowTopDiff;

        //NOTE: use integer division when possible. This code is frequently executed
        int arrowWidth = (arrow.getIntrinsicWidth() * 6) / 10;  
        int arrowHeight = (arrow.getIntrinsicHeight() * 6) / 10;
        int arrowRight = arrowLeft + arrowWidth;
        int arrowBottom = arrowTop + arrowHeight;

        arrow.setBounds(arrowLeft, arrowTop, arrowRight, arrowBottom);

        canvas.save();
        //set rotation pivot at the center of the arrow image
        canvas.rotate(heading, arrowLeft + arrowWidth/2, arrowTop + arrowHeight / 2);

        Rect rect = arrow.getBounds();
        arrow.draw(canvas);
        arrow.setBounds(rect);

        canvas.restore();

    }

}