I did a simple test today, with a camera preview and a View subclass
on top of it, in a FrameLayout. The View subclass simply draws a
number of white squares in it's onDraw method (see code below).
I expected five white squares with varying transparency, but the
result is a number of squares with varying shades of grey. I recon
this is because the compositing done by the window manager uses an
xfermode of DST_IN or similar, where the destination color is
multiplied by the source alpha (Sa*Dc). For various reasons, I need
the behaviour to be something more like an overlay where the src alpha
is treated like a mask (imagine trying to make a viewfinder "peephole"
where the edges are translucent without darkening the preview pixels
underneath it).
Is this at all possible?
protected void onDraw(Canvas canvas) {
Paint p = new Paint();
for(int i=0; i < 5;i++) {
p.setColor(0xffffffff);
p.setAlpha(i*20);
canvas.drawRect(i*40, 100, i*40+40, 140, p);
}
super.onDraw(canvas);
}
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