David Bucciarelli wrote:
>
>> (Eero Wrote)
> > There has been some reports on R and B colours getting
> > mixed in glDrawPixels/glReadPixels on win32/glide based
> > Mesa. (In my case with V2, which might be significant
> > also)
> >
> > I am now seeing this bug "reliably" on my application:
> >
> > -when doing glReadPixels the R and B channel
> > datas are swapped.
> >
> > -the bug seems to "get started" when I do a
> > glDrawPixels operation.
> >
> > -after the pixels start reading in swapped fashion
> > they stay like that.
> >
> > I searched around in Mesa sources but could not find an
> > obvious reason for this. I currently suspect that
> > it is Glide which is somehow losing its "state".
> >
> > In Glide2 (at least) I did not find a way to directly
> > set the RGB/BGR state (or to inquire it) so I couldn't
> > do any tricks with the state directly.
>
> There could be two possible explanations:
>
> - someone has changed the grSstWinOpen() parameter for selecting RGB/BGR
> without changing the driver code for pixel operations (I'm at work
> without the Mesa sources at hand so I can not check);
>
> - the problem could be in the grLfbWriteColorFormat(GR_COLORFORMAT_ABGR)
> calls in driver functions for pixel operations. Some 3Dfx hardware
> doesn't support all color formats (i.e. I know it is true for the Voodoo
> Rush) and the Glide doesn't internally swap the color bytes for
> unsupported GR_COLORFORMAT. The driver is not handling this case and it
> always uses the some color format assuming it is supported.
>
> Are you using a Voodoo 3 ?
>
I am using Voodoo 2, but I think the situation is more interesting
than covered by the explanations you gave above.
Namely the first time I do glReadPixels the data is pretty reliably ok.
But when the same program latter does the read operation (same
subroutine)
the data is swapped! (also pretty reliably)
As I mentioned above I have some reason to suspect that the glDrawPixels
somehow causes the mode swap. Maybe glide changes some internal settings
for it but does not change them back.
Of course there is a possibility that my code somehow corrupts the glide
internal state... And/or the problemcan be specific to the Win95 glide
version.
Eero
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