alpha blending frame buffer


WizardStan

Mega GP Mania
Joined
May 24, 2008
Messages
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Has anyone figured out how to set the framebuffer to support alpha blending? I've tried setting "alpha_blending_enabled", using fbset to specify -rgba 5,5,5,1 and -rgba 8,8,8,8 (16 and 32 bit respectively) but it always remains default (5,6,5,0 and 8,8,8,0 respectively). For my overlay menu, I had to use a transparency colour, otherwise it would just cover the entire thing with black and you'd not see the underlying framebuffers. Ideally I'd prefer to use the alpha channel. The "global_alpha" setting works, suggesting that alpha blending is at least hardware supported, but I don't want it to be global, I want to specify individual pixels as invisible or not.


To be clear, I'm not looking for the SDL style alpha blending where it needs to manually blend two software layers into one framebuffer, I mean alpha blending on the three hardware framebuffers we have. I'm probably the only person who has looked into this on the Pandora, but I figured it wouldn't hurt to ask. Maybe someone has had experience on other systems?


If not, I'll stick with the colour key transparency. No fancy partial transparency, but I can work with it.
 
I don't think this is supported by the driver in any way, and IIRC hardware alpha support is weird, needs to switch to some mode where layers are reversed and then certain restrictions apply, so it might not be that useful in practice (I forget the details).
 
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I figured. I know it is somewhat possible, I can tweak the global alpha setting for the overlay, and maybe that's enough. On the other hand, maybe I should stop trying to make it "look cool" and worry about getting something actually functional, first. :p
 
I'll stick with the colour key transparency. No fancy partial transparency, but I can work with it.

You can get tricky and turn edge pixels on and off each frame for monochrome anti-aliasing...
 
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