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Index › Programming Questions & Help › Syntax Questions › 3d -> 2d transformation
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3d -> 2d transformation? (Read 923 times)
_ikaruga
3d -> 2d transformation?
Sep 16th, 2007, 1:07am  
if i call line(x0,y0,z0,x1,y1,z1); to draw a line in 3d, a transformation from 3d to the 2 dimentional space of my screen occures. Can i access this transformation?

Is there a function that takes in a 3d coordinate and returns the 2d coordinate it would be projected to?
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JohnG
Re: 3d -> 2d transformation?
Reply #1 - Sep 16th, 2007, 1:58am  
See screenX/screenY/screenZ, http://processing.org/reference/screenX_.html et al.
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_ikaruga
Re: 3d -> 2d transformation?
Reply #2 - Sep 16th, 2007, 3:23am  
omfg. i wish i'd noticed that the language section came in abridged & extended versions sooner Smiley

thanks!
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_ikaruga
Re: 3d -> 2d transformation?
Reply #3 - Sep 16th, 2007, 4:17am  
ok, why isn't this working? i'd like to perform a rotation about Y, compute the screen space coordinates of my 3d points, then draw that line in 2d using line() and screenX()/screenY(). so this is what i have:


float angle = 0;
void draw() {
 background(255);
 
 translate(width/2, height/2);
 rotateY(radians(angle));
 angle += 0.5;
 if(angle>360) {
   angle -= 360;
 }
 translate(-width/2, -height/2);
 
 
 float x0 = 0, y0 = height, z0 = 0,
       x1 = width, y1 = 0, z1 = 0;
 
 float s0X = screenX(x0,y0,z0), s1X = screenX(x1,y1,z1);
 float s0Y = screenY(x0,y0,z0), s1Y = screenY(x1,y1,z1);
 
 line(x0,y0,z0,x1,y1,z1);
 
 pushMatrix();
 line(s0X,s0Y,s1X,s1Y);
 popMatrix();
}


but the line i draw itself seems to get rotated itself. why do these lines diverge?
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JohnG
Re: 3d -> 2d transformation?
Reply #4 - Sep 16th, 2007, 1:44pm  
The 2D line is affected by the rotation, as well as the 3D one. The screenX/Y values you get are the position on screen, given *no* transformations.

You need to undo the rotations/transaltions before you draw the 2D one.

so you need to do something like:
Code:
void draw()
{
  pushMatrix(); //so we can go back to no transformations.
  translate(...);
  rotate(...);
  translate(..);
  x0=...; 
  //etc
  sx0=...;
  //etc
  line(...); //3D line
  
  popMatrix();
  // now we have the default settings.
  line(...); //2D line
}
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_ikaruga
Re: 3d -> 2d transformation?
Reply #5 - Sep 17th, 2007, 7:37am  
aaahh. ok, i had that backwards.
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