Re: NSColor question

[Fred Kiefer]

Chris B. Vetter wrote:
> Hi,
>
> I was trying to create a splash window, you know like Acroread displays
> during startup. For that, I figured to create a transparent window and
> add a content view that draws an irregular shape in -drawRect:
>
> Before working on the view I tried to create the transparent window,
> using the following:
>
>   color = [NSColor clearColor];
>
>   window = [[NSWindow alloc] initWithContentRect: rect
>              styleMask: NSBorderlessWindowMask
>              backing: NSBackingStoreBuffered
>              defer: NO];
>   [window setBackgroundColor: color];
>   [window setAlphaValue: 1.0];
>   [window setOpaque: NO];
>
>
> However, popping open the window, all I got was a _black_ background on
> back-art and a _white_ background on back-xlib.
>
> Looking at the source to NSColor, I saw that +clearColor really is just
> a [self colorWithCalibratedWhite: 0.0 alpha: 0.0]
>
> Playing around with various color settings I found out that both,
> +colorWithCalibratedWhite:alpha: and +colorWithDeviceWhite:alpha: do
> exactly the same thing: black on back-art, white on back-xlib, without
> any regard of the values passed for 'white' or 'alpha'.
> Using +setIgnoresAlpha: didn't seem to make a difference either.
>
> All the +<color>Color and +colorWith<whatever>:a:b:c: seem to work fine.
>
> Is this a known problem, or am I missing something?

Both X backends currently don't support an alpha value for the window 
itself, as X has no way of dealing with (half) transparent windows. Ok, 
there are ways to fake them even with X, but nobody has regarded this as 
worthwhile. What is interesting is, that both backends result in 
different colours being displayed instead. I have no idea, which is 
correcter.