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Newsgroups: comp.sys.apple2.programmer
Date: Mon, 24 Oct 2016 10:30:24 -0700 (PDT)
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Subject: Re: hi-res graphics animation, dynamically generated shape tables
From: Michael Pohoreski <michael.pohoreski@gmail.com>
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Xref: csiph.com comp.sys.apple2.programmer:3156

On Monday, October 24, 2016 at 9:01:44 AM UTC-7, Michael Pohoreski wrote:

Part 3b -- Supplement

> Our **integer** line drawing function ends up like:
> 
> function line2( x0, y0, x1, y1, color )
> {
>     var x, y = y0;
>     var dx = x1 - x0;
>     var dy = y1 - y0;
>     var s  = 2*dy - dx;
> 
>     for( x = x0; x <= x1; ++x )
>     {
>         putpixel( x, y, color );
> 
>         if (s > 0)
>         { 
>             s -= dx;
>             y++;
>         }
>         s += dy;
>     }
> }

Update:

In order to preserve symmetry, the compare should be: >= instead of >

if (s >= 0)

Check out linei() and linej() in line.js