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 11:40 +0100
Organization	A noiseless patient Spider
Message-ID	<mflql6$rh1$1@dont-email.me> (permalink)
References	<ba08a0b0-e761-430f-9c23-458f7f14667d@googlegroups.com> <e59b0d75-7803-4223-aefb-74988f23be81@googlegroups.com> <mfjcqk$cs2$1@dont-email.me> <mfk43f$clv$1@dont-email.me> <mfl6ra$j7$1@dont-email.me>

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On 03/04/2015 06:02, Richard Heathfield wrote:
> On 02/04/15 20:09, Bartc wrote:

> And if you're going to use floating point anyway, my philosophy has
> always been to use double, for much the same reason that we generally
> use int rather than short int unless there is a specific reason to do
> otherwise.

(When I first starting doing this stuff, floating point was done in 
software. Double-precision was much slower, and I didn't start using it 
until I was sure of hardware support. Even now, I'm not sure that even 
common processors such as ARM fully support it in hardware.)

>> But 3D introduces other complications too. Your scheme will do to get
>> started.)

>>> But wait! A face has a colour.
>>
>> Eventually. But when you think about a scheme where vertices, edges and
>> faces are separate, which have the colour? Maybe it makes more sense for
>> a face to have the colour, but usually faces also form part of a
>> continuous surface of a single colour. So it's a bit wasteful to repeat
>> the same colour hundreds of times.
>
> That makes a lot of sense. So where would *you* store the colour? I
> suppose we could store it in the object structure (that is, the struct
> that contains the high level details for the structure, such as its
> current position, velocity, and acceleration).

There is no straightforward answer about where to store the colour. It 
all depends.

Possibly bringing in 3D at this level was a mistake. In 2D, you don't 
really deal with individual triangular faces much. You tend to have 
lines and shapes, with outlines and solid fill, and these may be just 
geometry, or part of a stored model complete with attributes such as colour.

However even in 3D, if Ford were designing a new vehicle body full of 
complicated curved surfaces, would they store a fixed colour for it? 
Cars come in a variety of colours!

>> You mean draw the edges of the face? Filling the interior is a bit
>> harder.
>
> A little bit, yes. I would do it like this:
>
> 1) if your triangle does not have a horizontal side, split it into two
> triangles that share a horizontal side. Then call this routine twice,
> once for each triangle. Otherwise:
> 2) for each row of the triangle, find the leftmost and rightmost pixels
> to be affected, using something like Bresenham (or indeed Wu) to make
> this determination.
> 3) Colour each relevant pixel in the row, using a horizontal line-draw.

If floating point is part of this and scaling of these triangles is 
allowed, even in 2D, then it can get more elaborate. You might be zoomed 
in so much into the triangle that all you need to do is fill the frame 
with the colour. Or you're zoomed in just enough to end up drawing a 
7-sided irregular polygon.

At some point you will need to convert coordinates which might 
conceivably be at -2.581e233 (thanks to your doubles!), into something 
more practical. Otherwise, there might be an awful lot of pixels to 
process before some of them end up in the framebuffer.

For these sorts of reason, I would have different tiers of API, with an 
integer-based 2D API at the bottom. Although floating point is also 
viable with a bit more work, and the 2D system in PostScript works 
extremely well using floating point.

(I think PostScript keeps geometry and colour separate too! However the 
sort of API I have in mind wouldn't concern itself with an object model, 
and I'm not sure PS does either.)

-- 
Bartc

Thread

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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