Get zbuffer in Processing v2b6

Core Library Questions

damontic

Get zbuffer in Processing v2b6

in Core Library Questions • 10 months ago

Hi,

I am trying to access the zbuffer of a Scene in Processing 2b6.
The idea is to port this project to processing v2.

It seems that the object FloatBuffer hasn't got the array

zbuffer anymore.
So I tried with the commented code that tries to acces the zbuffer using OpenGL:

PGraphicsOpenGL pogl = (PGraphicsOpenGL) g;
FloatBuffer zbuff = FloatBuffer.allocate(1);
pogl.gl.glReadPixels( mouseX, mouseY, 1, 1, GL.GL_DEPTH_COMPONENT, GL.GL_FLOAT, zbuff);
float z = zbuff.get();

At first I had some issues with the 5fth parameter GL.GL_DEPTH_COMPONENT, but by switching it to GL2.GL_DEPTH_COMPONENT I solved that first obstacle.
But now I am receiving z = 1 for every mouse position.

Any ideas?

Thanks!

Replies(2)

andres

Re: Get zbuffer in Processing v2b6

10 months ago

first, one detail with the glReadPixels() call: you should use height - mouseY - 1 instead of mouseY, because of the inverted Y axis in Processing with respect to OpenGL.

Any of the two following code options are valid:

import java.nio.*;
void setup() {
size(640, 360, P3D);
fill(204);
}
void draw() {
lights();
background(0);
camera(30.0, 300, 220.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0);
noStroke();
box(90);
stroke(255);
line(-100, 0, 0, 100, 0, 0);
line(0, -100, 0, 0, 100, 0);
line(0, 0, -100, 0, 0, 100);
PGraphicsOpenGL pg = (PGraphicsOpenGL) g;
PGL pgl = pg.beginPGL();
FloatBuffer zbuff = FloatBuffer.allocate(1);
pgl.readPixels(mouseX, height - mouseY - 1, 1, 1, PGL.DEPTH_COMPONENT, PGL.FLOAT, zbuff);
float z = zbuff.get();
pg.endPGL();
println(z);
}

import java.nio.*;
import javax.media.opengl.GL;
import javax.media.opengl.GL2;
void setup() {
size(640, 360, P3D);
fill(204);
}
void draw() {
lights();
background(0);
camera(30.0, 300, 220.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0);
noStroke();
box(90);
stroke(255);
line(-100, 0, 0, 100, 0, 0);
line(0, -100, 0, 0, 100, 0);
line(0, 0, -100, 0, 0, 100);
PGraphicsOpenGL pg = (PGraphicsOpenGL) g;
PGL pgl = pg.beginPGL();
FloatBuffer zbuff = FloatBuffer.allocate(1);
pgl.gl.glReadPixels(mouseX, height - mouseY - 1, 1, 1, GL2.GL_DEPTH_COMPONENT, GL.GL_FLOAT, zbuff);
float z = zbuff.get();
pg.endPGL();
println(z);
}

But testing both on 2.0b6 I get 0 for all positions on the screen, so there seems to be something off here. But running them on the latest revision from the repo gives non-zero values that appear to be correct. So the upcoming 2.0b7 should solve this issue.

damontic

Re: Re: Get zbuffer in Processing v2b6

10 months ago

Yes it works!

The first implementation with the processing-core repo at google code worked.

The second one throwed an exception,

Caused by: java.lang.IncompatibleClassChangeError: Expected static field processing.opengl.PGL.gl
at:
pgl.gl.glReadPixels(mouseX, height - mouseY - 1, 1, 1, GL2.GL_DEPTH_COMPONENT, GL.GL_FLOAT, zbuff);

But anyways thank you very much Andrés

--
Ing. David Alberto Montaño

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