Try this...

NOTE 1: Given Processing and OPENGL's opposite coordinate systems, I have flipped the texture on the Y.
NOTE 2: Since the texture is part of the drawing, it creates a small feedback loop (press the mouse to see it).

Code Example

1. import codeanticode.glgraphics.*;
2. import javax.media.opengl.GL;
3. import processing.opengl.*;
4.  
5. GLTexture tex;
6.  
7. void setup() {
8.   size(800, 600, GLConstants.GLGRAPHICS);
9.   tex = new GLTexture(this, width, height);
10.   tex.setFlippedY(true);
11. }
12.  
13. void draw() {
14.   if (!mousePressed) background(255);
15.   fill(0);
16.   ellipse(mouseX, mouseY, 30, 30);
17.  
18.   GLGraphics renderer = (GLGraphics)g;
19.   renderer.beginGL();
20.   GL gl = renderer.gl;
21.   gl.glBindTexture(gl.GL_TEXTURE_2D, tex.getTextureID());
22.   gl.glCopyTexSubImage2D(gl.GL_TEXTURE_2D, 0, 0, 0, 0, 0, width, height);
23.   renderer.endGL();   
24.  
25.   fill(255, 0, 0);
26.   rect(10, 10, width/3+2, height/3+2);
27.   image(tex, 11, 11, width/3, height/3);
28. }

Thank you SO much, that's exactly what I needed.  Works perfectly.

The GLGraphics library facilitates the easy use of (pure) opengl calls. You could also fully do it yourself.

Your code relies on GLTexture, but you don't use the GLGRAPHICS renderer.

I had the same pb and used a GLGraphicsOffScreen to capture a OCD cam, applied some filters on it then render it using a texture...

I'm not sure this is making the best out of openGL capacities though, the display seems to be much slower than other experiments I've done with 3D and glgraphics. The whole openGL thing is still pretty obscure to me, just started few days back so any suggestions on the code are welcome!! Cheers.

1. import processing.opengl.*;
2. import codeanticode.glgraphics.*;
3. import damkjer.ocd.*;
4. GLTexture dest, src;
5. GLTextureFilter[] filters;
6. GLGraphicsOffScreen offscreen;
7. Camera cam;
8. int selFilter = 0;
9. float s = 0;
10. void setup() {
11.   size(1000, 800, GLConstants.GLGRAPHICS);
12.  
13.   PFont font = loadFont("Tahoma-18.vlw");
14.   textFont(font, 18);
15.   dest = new GLTexture(this, width, height);
16.  
17.   filters = new GLTextureFilter[7]; 
18.   filters[0] = new GLTextureFilter(this, "CrossHatch.xml");
19.   filters[1] = new GLTextureFilter(this, "Thermal.xml");
20.   filters[2] = new GLTextureFilter(this, "Toon.xml");
21.   filters[3] = new GLTextureFilter(this, "Dream.xml");
22.   filters[4] = new GLTextureFilter(this, "CrossStich.xml");
23.   filters[5] = new GLTextureFilter(this, "FreiChen.xml");
24.   filters[6] = new GLTextureFilter(this, "Sobel.xml");
25.  
26.   textureMode(NORMALIZED);
27.  
28.   cam = new Camera(this, 0, 0, 200);
29.  
30.   offscreen = new GLGraphicsOffScreen(this, width, height, true, 4); 
31.   
32.   frameRate(30);
33. }
34. void draw() {
35.   background(0);
36.  
37.   src = offscreen.getTexture();
38.   offscreen.beginDraw();
39.     offscreen.background(0);
40.     offscreen.lights();
41.     cam.circle(radians(noise(millis()*2)*noise(millis())*50));   
42.     cam.feed();
43.     // DRAW STUFF HERE
44.    
45.   offscreen.endDraw();
46.    
47.   filters[selFilter].apply(src, dest);
48.    
49.   beginShape(QUADS);
50.   texture(src);
51.   vertex(0, 0, 0, 0);
52.   vertex(mouseX, 0, float(mouseX)/width, 0);
53.   vertex(mouseX, height, float(mouseX)/width, 1);
54.   vertex(0, height, 0, 1); 
55.   endShape();
56.  
57.   beginShape(QUADS);
58.   texture(dest);
59.   vertex(mouseX, 0, float(mouseX)/width, 0);
60.   vertex(width, 0, 1, 0);
61.   vertex(width, height, 1, 1);
62.   vertex(mouseX, height, float(mouseX)/width, 1); 
63.   endShape();
64.  
65.   fill(255, 0, 0);  
66.   stroke(255, 0, 0);
67.   line(mouseX, 0, mouseX, height);
68.   text(filters[selFilter].getName(), 0, 20);
69.  
70. }
71. void keyPressed() {
72.   selFilter = (selFilter + 1) % filters.length;
73. }