[Scummvm-devel] Overlay handling

[Marcus Comstedt]

Max Horn <max at quendi.de> writes:

> Of course we can use an alpha channel w/o  
> kFeatureOverlaySupportsAlpha. Its sole function was to determine (in  
> the old GUI rendering code) where compositing happens: In the backend  
> or the "frontend" code.

Not fully accurate.  Even with an overlay with HW alpha, there was
still "frontend" compositing, if the GUI drew to the same place twice
using semitransparance.  The only difference between the two cases
was that with an overlay without alpha, the code could be simplified
by the assumption that the alpha of the existing overlay pixel would
always be 1.0.  No assumption could be made that the old alpha would
be 0.0 in the case with alpha overlays though, as the pixel could have
been painted to before.


  // Marcus