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Index › Programming Questions & Help › Syntax Questions › Camera and objects relative position
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Camera and objects relative position (Read 409 times)
olivier
Camera and objects relative position
Dec 5th, 2007, 10:50pm  
Hi all,
I confess that I'm unconfortable with the camera control.
Maybe somemone could explain where I'm wrong ?
I defined an object AerialCamera to handle a camera flying over the 2D plane (on X and Y axis). The idea is to be able to  "fly" over the plane, controlled by the mouse.

I tried severeal solutions. The one I share with you here is to move the object to be drawn, the camera being always at x=y=0. This let me use the rotate() functions
The problem I'm unable to solve is that once rotated on one axis, the other axis does not correspond to the axis I would like to rotate around.
Hmmm, well, maybe better understandable with an example.
See http://o.marce.free.fr/Processing/AerialCamera.pde


I draw a 4 colored square, then I try to control the rotation of the camera.

To play with it: mouse1 to move the object, mouse3 to change the view distance, shift+mouse2 to (try to) rotate the object such that I can fly above it.

Any idea, or better, solutions ?
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olivier
Re: Camera and objects relative position
Reply #1 - Dec 6th, 2007, 10:17pm  
Me again
Ok I found myself the answer to my question.

First answer is : use OCD library, dumb !!
(http://www.cise.ufl.edu/~kdamkjer/processing/libraries/ocd/)
Unfortunately it does not work for my Processing v135.
Got :
java.lang.IncompatibleClassChangeError
at damkjer.ocd.Camera.atan2(Camera.java:413)

Second (and correct) answer is to use beginCamera()/endCamera()
It apply the transformation to the camera rather than the objects. It is exactly what I'm looking for. Great !

Then, the draw() method of my AerialCamera object is now :
void draw(){
   beginCamera();
   camera(0,0,0.0001,0,0,0,0,1,0);
   rotateZ(alphaX);
   rotateX(-alphaZ);
   translate(0,0,ratioZ*eyeZ);
   endCamera();
}

The only point is that if I put :
   camera(0,0,0,0,0,0,0,1,0);
instead, it does not work... Why ?

Looks like a bug, no ? (indeed I put 0.0001 to workaround)
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antiplastik
Re: Camera and objects relative position
Reply #2 - Dec 7th, 2007, 9:39am  
That is not a bug. You're telling the renderer to put the camera at position (0, 0, 0) and look at (0, 0, 0) : hence it doesn't know which orientation to choose for the camera.

You shouldn't specify the same vectors for position and lookAt.

If you want the camera to look forward, try :

Code:
camera(
  0, 0, 0,  // camera position
  0, 0, 1,  // camera looking direction
  0, 1, 0   // camera 'up' vector
}
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