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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: chosing "small 2d graphics library"  interface
Date: Thu, 02 Apr 2015 10:47:36 -0700
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Richard Heathfield <rjh@cpax.org.uk> writes:
[...]
> #define NUM_DIMENSIONS 2
>
> struct point
> {
>   double dimension[NUM_DIMENSIONS];
> };
>
> For notational convenience, let's alias that type:
>
> typedef struct point Point;

[...]

> struct edge
> {
>   Point vertex[2];
> };
>
> and again, let's alias the type:
>
> typedef struct edge Edge;
>
> A "face" is a series of edges that, taken together, mark off a region
> of our universe. A face can have many edges, but it turns out to be
> convenient to restrict ourselves to three, forming a triangle. Why is
> this convenient? Well, firstly, we can use triangles to build up any
> other shape we want, so it doesn't cost us much, but more importantly
> we can specify exactly 3 of something really easily, whereas
> specifying n of anything requires us to play games with dynamic
> allocation. We will have to do that anyway at some time, but there's
> no need to have that level of complexity at this primitive a
> level. So:
>
> struct face
> {
>   Edge edge[3];
> };
>
> typedef struct face Face;
[...]

With this representation, a Face (representing a triangle) stores each
vertex point twice.  It can also represent a triangle whose edges are
disconnected, which I presume would be invalid.

I suggest:

    struct face
    {
      Point vertex[3];
    };

And perhaps "struct triangle" would be clearer than "struct face", since
you've already decided (reasonably IMHO) that all faces are triangles.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"