9fans - fans of the OS Plan 9 from Bell Labs
 help / color / mirror / Atom feed
From: maht <mattmobile@proweb.co.uk>
To: 9fans@9fans.net
Subject: [9fans] Porter-Duff alpha blending
Date: Thu,  5 Mar 2009 18:31:41 +0000	[thread overview]
Message-ID: <49B01A8D.6040308@proweb.co.uk> (raw)

Hi,

I decided to try some draw(2) exploration and I'm not getting what I
expected from alpha blending.

If I apply alpha to RGB24 images they change as expected but if I use
RGBA32 images and try to apply alpha it's going weird on me (or I am
weird on it).

If I apply setalpha(DRed, 0x7F) and then draw() it to screen instead of
being less red it goes blue!

I've posted some sample code and the outputs at
http://maht0x0r.blogspot.com/2009/03/o-that-way-madness-lies.html

Any explanations would hopefully be illuminating.

matt



             reply	other threads:[~2009-03-05 18:31 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-03-05 18:31 maht [this message]
2009-03-04 21:18 ` andrey mirtchovski
2009-03-04 23:24 ` Russ Cox
  -- strict thread matches above, loose matches on Subject: below --
2009-03-04 21:53 erik quanstrom
2009-03-04 22:01 ` andrey mirtchovski
2009-03-04 21:32 erik quanstrom
2009-03-04 21:37 ` andrey mirtchovski
2009-03-04 21:42   ` andrey mirtchovski
2009-03-04 21:44   ` erik quanstrom
2009-03-04 21:53     ` andrey mirtchovski
2009-03-04 22:03       ` erik quanstrom
2009-03-04 22:21         ` andrey mirtchovski
2009-03-04 22:22         ` Devon H. O'Dell
2009-03-04 22:45           ` andrey mirtchovski
2009-03-04 22:59             ` erik quanstrom
2009-03-04 23:05               ` andrey mirtchovski
2009-03-04 23:58             ` Charles Forsyth
2009-03-05  1:04               ` erik quanstrom
2009-03-05  1:29               ` andrey mirtchovski
2009-03-05  2:07                 ` andrey mirtchovski
2009-03-05  2:22                   ` erik quanstrom
2009-03-06  3:21                     ` andrey mirtchovski
2009-03-06 20:48                       ` Russ Cox
2009-03-06 21:42                         ` andrey mirtchovski
2009-03-08 22:33                           ` Jeff Sickel
2009-03-09 15:28                             ` Michaelian Ennis
2009-03-09 16:40                               ` Jeff Sickel
2009-03-09 14:00                         ` erik quanstrom
2009-03-09 15:32                           ` yy

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=49B01A8D.6040308@proweb.co.uk \
    --to=mattmobile@proweb.co.uk \
    --cc=9fans@9fans.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).