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Re: chosing "small 2d graphics library" interface

From Bartc <bc@freeuk.com>
Newsgroups comp.lang.c
Subject Re: chosing "small 2d graphics library" interface
Date 2015-04-03 01:06 +0100
Organization A noiseless patient Spider
Message-ID <mfklft$hpt$1@dont-email.me> (permalink)
References (7 earlier) <mfjik4$4d5$1@dont-email.me> <mfjj2d$5v8$1@dont-email.me> <f9e08937-c27d-40f8-9d36-b43fe471e0d6@googlegroups.com> <mfjrlk$aal$1@dont-email.me> <75c16b06-0701-455d-889a-0122b6c32f7c@googlegroups.com>

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On 02/04/2015 18:12, Malcolm McLean wrote:
> On Thursday, April 2, 2015 at 5:45:38 PM UTC+1, Richard Heathfield wrote:

>> It wouldn't have occurred to me to write twice to the same pixel in the
>> same operation. Is there an advantage to doing that?
>>
> It can make the code easier to write. If you're drawing a line with a joint in
> it from A to B to C, it's a lot easier if you can write to B.x, B.y twice without
> worrying that you'll get a double-opacity pixel.

That depends on what you mean by an 'alpha' component and what you do 
with it.

(To me, alpha or transparency is something that is used when displaying 
this image over another or over a background. If the image display is 
updated when writing to it, then if a pixel is set to red with 50% 
transparency, then after updating it again, it'll still be red with with 
50% transparency.)

What can affect being able to write twice is the drawing mode in effect 
for RGB, eg. 'xor' mode, or anything that modifies the current pixel 
rather than replaces it, such as making it /more/ red. This can be a 
problem even without a transparency channel.

-- 
Bartc

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chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-28 18:43 -0700
  Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-29 02:59 -0700
    Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 03:51 -0700
      Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-03-29 12:03 +0100
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 05:00 -0700
          Re: chosing "small 2d graphics library"  interface gof@somewhere.invalid (Gof) - 2015-04-01 08:02 +0000
            Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-01 09:40 +0100
              Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-01 04:04 -0700
      Re: chosing "small 2d graphics library"  interface Nobody <nobody@nowhere.invalid> - 2015-03-29 12:50 +0100
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 05:08 -0700
    Re: chosing "small 2d graphics library"  interface Jeff Higgins <jeff@invalid.invalid> - 2015-03-29 09:33 -0400
      Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 07:00 -0700
        Re: chosing "small 2d graphics library"  interface Jeff Higgins <jeff@invalid.invalid> - 2015-03-29 10:38 -0400
          Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 07:43 -0700
      Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 07:24 -0700
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 07:32 -0700
      Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-01 05:00 -0700
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-01 07:25 -0700
    Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 07:36 -0700
      Re: chosing "small 2d graphics library"  interface Jeff Higgins <jeff@invalid.invalid> - 2015-03-29 14:33 -0400
        Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-29 12:36 -0700
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-03-29 13:01 -0700
  chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-02 04:12 -0700
    Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 04:56 -0700
      Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 05:10 -0700
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 05:31 -0700
        Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 09:40 -0700
    Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 13:32 +0100
      Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 05:50 -0700
        Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 14:01 +0100
          Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 06:37 -0700
            Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 14:58 +0100
              Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-02 15:11 +0100
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 15:18 +0100
                Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-04-02 09:21 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 09:34 -0700
                Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-04-02 09:47 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 09:45 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 09:57 -0700
                Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-04-02 10:15 -0700
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 18:34 +0100
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 18:35 +0100
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 17:45 +0100
                Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-04-02 10:12 -0700
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 18:28 +0100
                Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-03 01:06 +0100
                Re: chosing "small 2d graphics library"  interface luser droog <luser.droog@gmail.com> - 2015-04-02 17:05 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 07:51 -0700
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 15:56 +0100
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 08:14 -0700
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 16:25 +0100
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 08:45 -0700
                Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 17:00 +0100
                Re: chosing "small 2d graphics library"  interface Keith Thompson <kst-u@mib.org> - 2015-04-02 13:03 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-05 14:25 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 09:06 -0700
                Re: chosing "small 2d graphics library"  interface Rosario19 <Ros@invalid.invalid> - 2015-04-02 18:22 +0200
                Re: chosing "small 2d graphics library"  interface Rosario19 <Ros@invalid.invalid> - 2015-04-02 18:40 +0200
                Re: chosing "small 2d graphics library"  interface Robert Wessel <robertwessel2@yahoo.com> - 2015-04-03 00:20 -0500
                Re: chosing "small 2d graphics library"  interface Rosario19 <Ros@invalid.invalid> - 2015-04-04 10:35 +0200
                Re: chosing "small 2d graphics library"  interface CHIN Dihedral <dihedral88888@gmail.com> - 2015-04-04 09:53 -0700
                Re: chosing "small 2d graphics library" interface Noob <root@127.0.0.1> - 2015-04-03 14:27 +0200
                Re: chosing "small 2d graphics library" interface fir <profesor.fir@gmail.com> - 2015-04-03 05:38 -0700
              Re: chosing "small 2d graphics library"  interface Jeff Higgins <jeff@invalid.invalid> - 2015-04-02 19:23 -0400
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-02 23:46 -0700
      Re: chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-02 08:03 -0700
        Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-02 16:14 +0100
          Re: chosing "small 2d graphics library"  interface Keith Thompson <kst-u@mib.org> - 2015-04-02 12:42 -0700
          Re: chosing "small 2d graphics library"  interface CHIN Dihedral <dihedral88888@gmail.com> - 2015-04-03 14:27 -0700
            Re: chosing "small 2d graphics library"  interface Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-04-03 14:50 -0700
      Re: chosing "small 2d graphics library"  interface Keith Thompson <kst-u@mib.org> - 2015-04-02 10:47 -0700
      Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-02 20:09 +0100
        Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-03 06:02 +0100
          Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-03 11:40 +0100
            Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-03 03:52 -0700
              Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-03 12:05 +0100
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-03 04:36 -0700
                Re: chosing "small 2d graphics library"  interface Bartc <bc@freeuk.com> - 2015-04-03 13:28 +0100
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-03 06:04 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-03 07:28 -0700
                Re: chosing "small 2d graphics library"  interface fir <profesor.fir@gmail.com> - 2015-04-03 12:43 -0700
            Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-03 12:57 +0100
      Re: chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-03 22:25 -0700
        Re: chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-03 22:34 -0700
          Re: chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-03 23:09 -0700
            Re: chosing "small 2d graphics library"  interface Richard Heathfield <rjh@cpax.org.uk> - 2015-04-04 09:23 +0100
    chosing "small 2d graphics library"  interface asetofsymbols@gmail.com - 2015-04-02 07:26 -0700

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