I am creating a pixel-hunting game. So my activity shows an ImageView. And I want to create a hint "show me where is the object". For this I need to blur whole image except a circle around a point where the object is located. Instead of blur I can show a just semitransparent black background. There is there is no problem to draw a semitransparent rectangle on the Canvas. But I don't know how to crop a transparent circle from it. The result should look like like this:
Please help me to achieve same result on Android SDK.
So finally I managed to do this.
Firstly I draw a semitransparent black rectangle on whole view.
After that using PorterDuff.Mode.CLEAR
I cut a transparent circle to show cat's position.
I had problem with PorterDuff.Mode.CLEAR
: firstly I was getting a black circle instead of a transparent one.
Thanks to Romain Guy's comments here: comment here I understood that my window is opaque and I should draw on another bitmap. And only after draw on View
's canvas.
Here is my onDraw
method:
private Canvas temp;
private Paint paint;
private Paint p = new Paint();
private Paint transparentPaint;
private void init(){
Bitmap bitmap = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_8888);
temp = new Canvas(bitmap);
paint = new Paint();
paint.setColor(0xcc000000);
transparentPaint = new Paint();
transparentPaint.setColor(getResources().getColor(android.R.color.transparent));
transparentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
}
protected void onDraw(Canvas canvas) {
temp.drawRect(0, 0, temp.getWidth(), temp.getHeight(), paint);
temp.drawCircle(catPosition.x + radius / 2, catPosition.y + radius / 2, radius, transparentPaint);
canvas.drawBitmap(bitmap, 0, 0, p);
}