Re: [9fans] Attempt at making 3D graphics library

[Pietro Gagliardi <pietro10@mac.com>]

On Nov 24, 2007, at 1:57 AM, Paul Lalonde wrote:

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> It's hard to tell what might be wrong with your transformation if  
> you don't also show the transformation matrix you are using,  
> including the camera parameters.  What you probably want is for  
> your transform to go from some world space coordinates (your 5,5,5)  
> to screen space.  It's also not clear if you are expecting device  
> coordinates (0..1023, 0..767) or normalized coordinates (0..1,  
> 0..1).   Your resulting coordinates aren't too far off for some  
> camera vaguely pointing at the origin and a device coordinate  
> transformation matrix.
>
> Paul
>
>

I was using no transformation matrix. I'm also thinking I'm getting  
the screen width and height wrong. Either way, there are formulae in  
the middle of that article, reproduced here:

.EQ
x sub { 2d } -> x sub { 3d } * { N over z } + { { screenwidth } over 2 }
.EN
.EQ
y sub { 2d } -> y sub { 3d } * { N over z } + { { screenwidth } over 2 }
.EN

It also says at the top that z=N and because equivalence is  
bidirectional that N=z. I do expect device coordinates.

I remember a while back about a discussion on 3D graphics  
programming. Andrey said that OpenGL was ported a long time ago but  
was never tied to rio or 8 1/2. He also said that it would be doable  
but difficult via APE. Unfortunately, I don't know how to program  
OpenGL, and by the code I've seen to produce a single object in a  
display I'm afraid of approaching it. I was hoping my simple point  
conversion mechanism would light a spark. Guess I'll try again later :-)