I'm trying to create a custom View which works simple: there is a Bitmap which is revealed by arc path - from 0deg to 360deg. Degrees are changing with some FPS.
So I made a custom View with overridden onDraw()
method:
@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
canvas.drawArc(arcRectF, -90, currentAngleSweep, true, arcPaint);
arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(bitmap, circleSourceRect, circleDestRect, arcPaint);
}
arcPaint
is initialized as follows:
arcPaint = new Paint();
arcPaint.setAntiAlias(true);
arcPaint.setColor(Color.RED); // Color doesn't matter
Now, everything draws great, but... the background is BLACK in whole View.
If I set canvas.drawColor(..., PorterDuff.Mode.DST)
and omit canvas.drawBitmap()
- the arc is drawn properly on transparent background.
My question is - how to set PorterDuff
modes to make it work with transparency?
Of course bitmap
is 32-bit PNG with alpha channel.
PorterDuff.Mode.CLEAR
doesn't work with hardware acceleration. Just set
view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
Works perfectly for me.