Re: [9fans] draw and Porter-Duff compositing algebra

Re: [9fans] draw and Porter-Duff compositing algebra

[Russ Cox]

I added the operators to draw.h along with space in
the devdraw protocol to send them, but haven't done
any implementation.  I don't actually think it would
be so hard, but I haven't had a driving need and other
things have taken my time.  If performance is not too
much of an issue, it wouldn't be so hard to add the
necessary code to alphadraw in /sys/src/libmemdraw/draw.c.
You'd have to define a bunch more Calcfns in the manner
of alphacalc for each operator, or you could generalize
alphacalc if that wasn't too inefficient.  Given the current
code, it probably wouldn't be noticeable.

The real reason I haven't done it is that I'd like to
get good performance on the trivial cases (like the Zero
operator), but that requires lots of special case
handling that I haven't yet enumerated.

Russ

Re: [9fans] draw and Porter-Duff compositing algebra

[forsyth]

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you'll find that the operator names now appear in
/sys/include/draw.h, awaiting only the implementation ...

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To: 9fans@cse.psu.edu
Subject: [9fans] draw and Porter-Duff compositing algebra
Date: Wed, 12 Jun 2002 18:29:11 +0100 (BST)
Message-ID: <20020612172911.34918.qmail@web21403.mail.yahoo.com>

Hallo,

 From my reading of they apropriate man
pages, I understand that the Plan 9 graphics
system uses the concepts from the
Porter-Duff compositing model, with the
matte described by the alpha channel.

Why however, is not the whole compositn
algebra implemented (all 11(?) operations
and 'plus'), and plan 9 only implement the
'over' operator ?

Thanks miuch
--Elizabeth


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[9fans] draw and Porter-Duff compositing algebra

[Elizabeth Strumph]

Hallo,

 From my reading of they apropriate man
pages, I understand that the Plan 9 graphics
system uses the concepts from the
Porter-Duff compositing model, with the
matte described by the alpha channel.

Why however, is not the whole compositn
algebra implemented (all 11(?) operations
and 'plus'), and plan 9 only implement the
'over' operator ?

Thanks miuch
--Elizabeth


__________________________________________________
Do You Yahoo!?
Everything you'll ever need on one web page
from News and Sport to Email and Music Charts
http://uk.my.yahoo.com