From: "Russ Cox" <rsc@swtch.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] libdraw α differences between plan 9 and p9p
Date: Fri, 31 Mar 2006 13:09:06 -0500 [thread overview]
Message-ID: <68bce97ae7814385cce7ecbc3a87baa6@swtch.com> (raw)
In-Reply-To: <58016f906ee4ee8db79b500cdecbe236@quanstro.net>
> 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.
prev parent reply other threads:[~2006-03-31 18:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-31 17:16 erik quanstrom
2006-03-31 18:09 ` Russ Cox [this message]
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