Stopping transparent drawing going all the way through NSViews

I'm doing some simple drawing in my NSView's drawRect with code like this

[[NSColor colorWithCalibratedWhite:0.250 alpha:0.700] set];
NSRectFill(dRect);

This drawing is being done in a nested view and I'm finding that the transparency goes all the way through the parent view and w开发者_如何学编程indow showing some of the screen beneath it.

How do I get it so the transparency only goes through to the parent view (or any drawing that was done in that frame before it?

Thanks!

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You really shouldn't be using NSRectFill to draw a transparent color. A call to

NSRectFill(rect);

is really just a shortcut to

NSRectFillUsingOperation(rect, NSCompositeCopy);

NSCompositeCopy doesn't perform compositing, so you can get unexpected results when a transparent NSColor is set.

Try using this instead:

[[NSColor colorWithCalibratedWhite:0.250 alpha:0.700] set];
[NSBezierPath fillRect:rect];

That should draw the transparency properly, with the underlying drawing visible.