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Topic: translates, rotates and keeping it in perspective (Read 296 times) |
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jedierikb
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translates, rotates and keeping it in perspective
« on: Dec 20th, 2003, 3:19pm » |
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anyone have tips on how to accomplish this trick? I want two X-rotated rectangles to look identical on screen, one on top of the other.
here is the code that doesn't do it:
void setup()
{
size( 400, 400 );
background( 40, 80, 120 );
stroke( 250, 20, 50 );
//this is rotated to the desired position
rectMode( CENTER_DIAMETER );
translate( width/2, height/2 );
rotateX( PI/3 );
rect( 0, 0, 100, 100 );
rotateX( -(PI/3) );
translate( -(width/2), -(height/2) );
//this is not. i would like it to appear
//identical to the previous rect,
//just directly above it.
//in other words, the same graphic as above,
//just shifted up a few 100 pixels
rectMode( CENTER_DIAMETER );
translate( width/2, height/4 );
rotateX( PI/3 );
rect( 0, 0, 100, 100 );
rotateX( -(PI/3) );
translate( -(width/2), -(height/4) );
}
any suggestions? thanks much.
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TomC
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Re: translates, rotates and keeping it in perspect
« Reply #1 on: Dec 20th, 2003, 6:10pm » |
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OK, your code draws two identical rectangles, one above the other. Because of perspective, they look different. You don't want that?
If you want two shapes as you have specified them to look identical on screen, you're going to need to find out about Orthographic Projection. I'm not sure if processing can do that, but it's not too hard to do for yourself...
Alternatively, if you are asking how to specify two shapes so that they look identical in spite of the perspective projection, then I have two suggestions...
1. Fake it, by drawing trapeziums in 2D instead of rectangles in 3D (easiest).
2. Fake it, by trial and error work out a different rotation which makes the second one look the same (harder, but only because it's time consuming).
3. Fake it, by working out the camera projection in reverse. (Hard, never done it).
Oh, a quick tip... where you have:
Code:
translation(x,y);
rotation(a);
rect(...);
rotation(-a);
translation(-x,-y);
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the same thing can be accomplished with:
Code:
push(); // remember the current transform
translation(x,y);
rotation(a);
rect(...);
pop(); // restore the transform from the last push()
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Hope that helps,
Tom.
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TomC
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Re: translates, rotates and keeping it in perspect
« Reply #2 on: Dec 20th, 2003, 9:06pm » |
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OK, talking to myself here, but here's a possible solution - just scale the z axis to something tiny. I don't know how flexible/robust it is, but it's worth playing around with.
Code:
void setup()
{
size( 400, 400 );
background( 40, 80, 120 );
stroke( 250, 20, 50 );
fill( 255 );
rectMode( CENTER_DIAMETER );
push();
scale( 1.0, 1.0, 0.00001 ); // this squishes everything onto the x-y plane
//this is rotated to the desired position
push();
translate( width/2, height/2 );
rotateX( PI/3 );
rect( 0, 0, 100, 100 );
pop();
// this is the same, but higher up
push();
translate( width/2, height/4 );
rotateX( PI/3 );
rect( 0, 0, 100, 100 );
pop();
pop();
}
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