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); }
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