| Re: [AD] getpixel conflict with alpha blended sprites |
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On November 17, 2003 03:23 am, Eric Botcazou wrote:
> > However, if the bitmap has an alpha channel and happens to be fully
> > opaque and white (ie 32-bit colour value 0xFFFFFFFF) then it looks like
> > -1 to the code and aborts my function, thinking it's out of the bitmap's
> > area.
>
> Very classical problem.
>
> > So what I'm asking is, would it be ok to modify _linear_getpixel32 in
> > igfx32.s to automatically AND its return value with 0x00FFFFFF, to
> > effectively strip out the alpha channel? Or is there a better way around
> > this?
>
> I can't think of any. The same mask should be (conditionally) applied in
> src/c/cgfx.h and the documentation updated to reflect that getpixel()
> doesn't return the alpha channel (if any). Or, probably better, that all
> drawing primitives (as listed in "Drawing primitives" in the docs) don't
> take into account the alpha channel.
>
Or maybe they only touch the alpha when the set_write_alpha_blender() is in
use?
--
Thomas Fjellstrom
tfjellstrom@xxxxxxxxxx
http://strangesoft.net