Processing 1.0 - Processing Discourse - Obtaining the View Frustum

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Index › Programming Questions & Help › OpenGL and 3D Libraries › Obtaining the View Frustum

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Obtaining the View Frustum (Read 887 times)

liminal

Obtaining the View Frustum
Feb 19^th, 2006, 4:54am

I'm trying to obtain the view frustum from the projection and modelview matrices, but don't seem to be getting it right. Can anyone with a better understanding of these matrices and how p5 implements them help me out?

My planes use the form ax + by + cz + d = 0 and I've been using the following code:

public Frustum(PGraphics3 g) {

PMatrix mvMat = g.modelview;
PMatrix projMat = g.projection;

PMatrix combo = new PMatrix(mvMat);
combo.apply(projMat);

Plane leftPlane = new Plane(
combo.m30 + combo.m00,
combo.m31 + combo.m01,
combo.m32 + combo.m02,
combo.m33 + combo.m03);

Plane rightPlane = new Plane(
combo.m30 - combo.m00,
combo.m31 - combo.m01,
combo.m32 - combo.m02,
combo.m33 - combo.m03);

Plane topPlane = new Plane(
combo.m30 - combo.m10,
combo.m31 - combo.m11,
combo.m32 - combo.m12,
combo.m33 - combo.m13);

Plane bottomPlane = new Plane(
combo.m30 + combo.m10,
combo.m31 + combo.m11,
combo.m32 + combo.m12,
combo.m33 + combo.m13);

Plane nearPlane = new Plane(
combo.m30 + combo.m20,
combo.m31 + combo.m21,
combo.m32 + combo.m22,
combo.m33 + combo.m23);

Plane farPlane = new Plane(
combo.m30 - combo.m20,
combo.m31 - combo.m21,
combo.m32 - combo.m22,
combo.m33 - combo.m23);

This is based on the info I found in http://www2.ravensoft.com/users/ggribb/plane%20extraction.pdf

Any help is much appreciated. Thanks!

fry

Re: Obtaining the View Frustum
Reply #1 - Feb 19^th, 2006, 3:14pm

why not just set the viewing frustum yourself? this is the doc for it:
http://dev.processing.org/reference/core/javadoc/processing/core/PGraphics3.html#frustum(float,%20float,%20float,%20float,%20float,%20float)

you can look through the source of PGraphics3 to see how it's used. i assume the example you're looking at is based on opengl or something like that, but we don't set things up exactly the way gl does.

liminal

Re: Obtaining the View Frustum
Reply #2 - Feb 20^th, 2006, 12:14am

I'm trying to obtain the frustum plane equations so that I can do my own view-dependent culling before sending geometry through the pipeline. I have a terrain I've divided up with a quad-tree and need to be able to zoom in and add detail to only the portions in view, while not rendering those outside the view.

I realize its asking a lot, but I'm stuck here on these transformations. Can you or someone take a look and suggest the correct solution?

Thanks again.

liminal

Re: Obtaining the View Frustum
Reply #3 - Feb 21^st, 2006, 7:43am

I figured out what was going wrong.

Changing the combined projection and modelview matrices to be:

PMatrix combo = new PMatrix(projMat);
combo.apply(mvMat);

works fine.

I picked this up by looking at how the undocumented and uncommented functions screenX/Y/Z() in PGraphics3 work. I guess that's what you get for working with beta software. sigh.

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