From:	Ludvig Larsson <ludvig AT club-internet DOT fr>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: perspective
Date:	Sat, 17 Oct 1998 05:40:11 +0200
Organization:	Faas-Goldhart
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jud wrote:
> 
> im making a cad type program and i was wondering if any of you know a good
> algorithm for calculationg perspective

Well, make the translations needed to get your screencoordinates(like
translation and rotations) then either use the matrix:

1  0  0  0
0  1  0  0
0  0  0 -1/d
0  0  0  1

where (0,0,d) is the projection plane.

or (same thing but without the use of a matrix):

multiply all x and y (after the translations) with 
the z-coordinate *(-d)

I think

s=0;
if(1-z/5000>0)
 s=1/(1-z/5000);
x=x*s;
y=y*s;

(and then just translate the coordinates to the center of the
screen(like x+=320;y+=240; in a 640x480 window))

will work, but it's just ripped out of an old code so I don't know if
it'l work or not...

Hop it helped anyway.

Ludvig Larsson

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