* Re:_[9fans]_libdraw_α_differences_between_plan_9__and_p9p
@ 2006-03-31 18:52 erik quanstrom
2006-03-31 22:03 ` _[9fans]_libdraw_α_differences_between_plan_9__and_p9p andrey mirtchovski
0 siblings, 1 reply; 5+ messages in thread
From: erik quanstrom @ 2006-03-31 18:52 UTC (permalink / raw)
To: 9fans
the answer is i didn't understand that there was a bug in the draw
library; i was not sure if there was a little hidden magic on plan9 that
made that work
- erik
On Fri Mar 31 12:09:26 CST 2006, rsc@swtch.com wrote:
> > i've noticed a difference in how the α channel looks in p9p vs.
> > plan 9. for example when porting mahjongg to plan9port,
> > i need to make this change to make the selection highlighting
> > apparent:
> >
> > - selected = eallocimage(one, 1, RGBA32, setalpha(DPalebluegreen, 0x5f));
> > + selected = eallocimage(one, 1, RGBA32, setalpha(DPalebluegreen, 0x9f));
> >
> > is a mapping needed to convert libdraw α values to X?
>
> This is the wrong question. The right question is why you
> changed this line:
>
> if(level.board[d][x][y].clicked)
> - draw(img, r, selected, nil, ZP);
> + draw(img, r, selected, selected, ZP);
>
> Since you're drawing selected through itself, you're effectively
> squaring the alpha, and (0x9F^2)/255 is approximately 0x5F, so
> this change necessitates the first one.
>
> I see why you changed the draw call, though, since on X, it
> just ignored the alpha channel in selected and just draws
> a big solid-color rectangle over the tile. This was due to a
> bug in the X wrappers around libdraw and is now fixed.
>
> Russ
>
> P.S. Upas/marshal encodes subjects "correctly" now too.
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: _[9fans]_libdraw_α_differences_between_plan_9__and_p9p
2006-03-31 18:52 erik quanstrom
@ 2006-03-31 22:03 ` andrey mirtchovski
2006-03-31 22:13 ` _[9fans]_libdraw_α_differ ences_between_plan_9__and_p9p Russ Cox
0 siblings, 1 reply; 5+ messages in thread
From: andrey mirtchovski @ 2006-03-31 22:03 UTC (permalink / raw)
To: Fans of the OS Plan 9 from Bell Labs
i hit that bug too when writing mahjongg (in drawterm, not in p9p). i
also didn't understand what was happening and simply did a workaround
(the -c argument, i believe) to force it in 32-bit mode...
you're not alone :)
On 3/31/06, erik quanstrom <quanstro@quanstro.net> wrote:
> the answer is i didn't understand that there was a bug in the draw
> library; i was not sure if there was a little hidden magic on plan9 that
> made that work
>
> - erik
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: _[9fans]_libdraw_α_differ ences_between_plan_9__and_p9p
2006-03-31 22:03 ` _[9fans]_libdraw_α_differences_between_plan_9__and_p9p andrey mirtchovski
@ 2006-03-31 22:13 ` Russ Cox
2006-03-31 23:06 ` quanstro
0 siblings, 1 reply; 5+ messages in thread
From: Russ Cox @ 2006-03-31 22:13 UTC (permalink / raw)
To: 9fans
>> the answer is i didn't understand that there was a bug in the draw
>> library; i was not sure if there was a little hidden magic on plan9 that
>> made that work
if a function call behaves differently between plan 9 and p9p
for no obvious & documented reason, that's always a bug.
the new drawterm works around this by turning off most of
the X optimizations. i got tired of working around the early
OS X X server.
russ
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re:__[9fans]_libdraw_α_differ_ences_between_plan_9__and_p9p
2006-03-31 23:06 ` quanstro
@ 2006-03-31 22:51 ` Charles Forsyth
0 siblings, 0 replies; 5+ messages in thread
From: Charles Forsyth @ 2006-03-31 22:51 UTC (permalink / raw)
To: 9fans
> i didn't have plan 9 at the time to compare.
there is no comparison
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re:__[9fans]_libdraw_α_differ_ences_between_plan_9__and_p9p
2006-03-31 22:13 ` _[9fans]_libdraw_α_differ ences_between_plan_9__and_p9p Russ Cox
@ 2006-03-31 23:06 ` quanstro
2006-03-31 22:51 ` Re:__[9fans]_libdraw_α_differ_ences_between_plan_9__and_p9p Charles Forsyth
0 siblings, 1 reply; 5+ messages in thread
From: quanstro @ 2006-03-31 23:06 UTC (permalink / raw)
To: 9fans
i didn't have plan 9 at the time to compare.
- erik
On Fri Mar 31 16:15:10 CST 2006, rsc@swtch.com wrote:
> >> the answer is i didn't understand that there was a bug in the draw
> >> library; i was not sure if there was a little hidden magic on plan9 that
> >> made that work
>
> if a function call behaves differently between plan 9 and p9p
> for no obvious & documented reason, that's always a bug.
>
> the new drawterm works around this by turning off most of
> the X optimizations. i got tired of working around the early
> OS X X server.
>
> russ
>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2006-03-31 23:06 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2006-03-31 18:52 erik quanstrom
2006-03-31 22:03 ` _[9fans]_libdraw_α_differences_between_plan_9__and_p9p andrey mirtchovski
2006-03-31 22:13 ` _[9fans]_libdraw_α_differ ences_between_plan_9__and_p9p Russ Cox
2006-03-31 23:06 ` quanstro
2006-03-31 22:51 ` Re:__[9fans]_libdraw_α_differ_ences_between_plan_9__and_p9p Charles Forsyth
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