Read ZBuffer

Graphics and GPU Programming Programming

Started by Phy March 28, 2005 07:02 AM

6 comments, last by Phy 19 years ago

139

Author

March 28, 2005 07:02 AM

Is there a way to read from the zbuffer? I'm trying to do pointsprite visibility testing for a neato effect, but can't find anyway to do it.

Aeluned

196

March 28, 2005 09:02 AM

glReadPixels using the GL_DEPTH_COMPONENT enum.

Phy

139

Author

March 28, 2005 09:41 AM

Kind of a newbie question, but how do I convert vertex coordinates to screen coordinates and a z value?

Aeluned

196

March 28, 2005 09:49 AM

You can get the screen coordinates by multiplying the vertex by the ModelviewProjection matrix. To obtain the transformed z position of your vertex, multiply the vertex by the Modelview matrix.

z position makes no sense when considering screen coordinates.

Phy

139

Author

March 28, 2005 10:05 AM

I can't get the values to work right, whats the tag for code and I'll post it here?

Aeluned

196

March 28, 2005 10:08 AM

sorry, don't know how to post code :(

_the_phantom_

11,263

March 28, 2005 10:10 AM

then you should both check out the Forum FAQ [grin]

Phy

139

Author

March 28, 2005 10:11 AM

float mtx[16];			glGetFloatv( GL_MODELVIEW_MATRIX, mtx );			tpos[0] = mtx[0]*ptcl->pos[0] + mtx[1]*ptcl->pos[1] + mtx[2]*ptcl->pos[2] + mtx[3];			tpos[1] = mtx[4]*ptcl->pos[0] + mtx[5]*ptcl->pos[1] + mtx[6]*ptcl->pos[2] + mtx[7];			tpos[2] = mtx[8]*ptcl->pos[0] + mtx[9]*ptcl->pos[1] + mtx[10]*ptcl->pos[2] + mtx[11];			glGetFloatv( GL_PROJECTION_MATRIX, mtx );			tpos[0] = mtx[0]*tpos[0] + mtx[1]*tpos[1] + mtx[2]*tpos[2] + mtx[3];			tpos[1] = mtx[4]*tpos[0] + mtx[5]*tpos[1] + mtx[6]*tpos[2] + mtx[7];			tpos[2] = mtx[8]*tpos[0] + mtx[9]*tpos[1] + mtx[10]*tpos[2] + mtx[11];			float fBuffValue;			glReadPixels( tpos[0], tpos[1], 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &fBuffValue );			if ( fBuffValue < tpos[2] )				ptcl = ptcl->nextParticle;

good thing you can 'try' and edit other peoples posts =)

Read ZBuffer

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Read ZBuffer

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