[cairo] W32: Drawing globally-transparent stuff with cairo

[LRN]

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On 27.03.2014 19:54, LRN wrote:
> I've been trying to somehow hack GTK to have RGBA GdkWindows, with
>  mixed results so far (i either get massive alpha corruption, or 
> crash pixman inside bitblt).
> 
> Decided to take a step back and see if i can make it work 100% 
> correctly with just GDI & cairo. Turns out, i can't.
> 
> I've attached an example, compile with gcc main.c -o main.exe 
> -I/mingw/include/cairo -lcairo -lgdi32 -ldwmapi
> 
> It draws two gradients - one transparent, and one opaque. 
> Transparency only works when window is invalidated and repainted 
> (such as when it is obscured by another window and later shown 
> again).
> 
> The problem is most likely W32-specific, and not directly related 
> to cairo, but i simply can't find what is wrong :(
> 

I'd like to thank everyone for the help.

The problem was mostly in W32 display config (glass transparency not
enabled).

I'm now convinced that the rest of my problems are due to a bug in
cairo/pixman.

GTK bug tracking this is:
https://bugzilla.gnome.org/show_bug.cgi?id=727316

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