Android draw on camera preview

Question

I\'m making a virtual reality application where the camera should detect faces, locate them and show their location on the camera preview.

I know of 3 ways to do it,

Answer 1

I could said,

It's not about a Thread.

It not because of this line that make error either.

canvas.drawPoint(leftEye.x, leftEye.y, red);

It because of the canvas still using and can't lock it

If you carefully check, you will see this canvas you get is == null

canvas = canvasHolder.lockCanvas();
    if (canvas == null)  Log.i("Error", "Canvas == null!"); 

You might have question then where is it already use?

It already use to display to show what's going on to you! That is

camera.setPreviewDisplay(previewHolder);

So, I suggest, If you want to draw Point over your eye, you might need to have another SurfaceView / SurfaceHolder over you SurfaceView for preview camera :]