Re: [AD] getpixel conflict with alpha blended sprites

[Eric Botcazou <ebotcazou@xxxxxxxxxx>]

> 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.

-- 
Eric Botcazou