NSColor alpha value darkens color

Question

I am trying to fill an NSRect in a subview with a translucent color. I am using:

[[NSColor colorWithCalibratedWhite:1 alpha:0.5]set];

But the alpha value doesn't make it transparent but just darker. Using an alpha value of 0 simply gives black. I have used this code many times before and i do not know why it is not working.

Thank you in advance, Ben.

Answer 1

The color appears darker because the context itself is not transparent, you're seeing the blacks bleed through behind the transparency. You need to use this operation:

NSRectFillUsingOperation(theRect, NSCompositeSourceOver);