import codeanticode.glgraphics.*;
import processing.opengl.*;

GLGraphicsOffScreen one;
GLTexture oneTex,twoTex;

int w=400,h=200;
void setup(){
  
  size(w*2,h,GLConstants.GLGRAPHICS);
  one = new GLGraphicsOffScreen(this, w, h);

  oneTex = new GLTexture(this,w,h);
  twoTex=new GLTexture(this,w,h);//
}

void draw(){
  
  one.beginDraw();
  one.background(100,100,255);
  one.fill(255,0,0);
  one.ellipse(mouseX,mouseY,20,20);
  one.endDraw();

  oneTex=one.getTexture();
  image(oneTex, 0,0);

  // ------------------------------------------
  // copying pixels form one texture to another

  oneTex.loadPixels();
  oneTex.updateTexture();

  twoTex.loadPixels();
  twoTex.updateTexture();

  for (int i = 0; i < w*h; i++) {
    if(red(oneTex.pixels[i])>127){
      twoTex.pixels[i]=color(255);
    }
  }
  
  oneTex.loadTexture();
  oneTex.updatePixels();

  twoTex.loadTexture();
  twoTex.updatePixels();

  image(twoTex,w,0);

  // CLEAR twoTex
  twoTex.loadPixels();
  twoTex.updateTexture();

  for (int i = 0; i < w*h; i++)
    twoTex.pixels[i]=color(0); // CLEAR twoTex SCREEN

  twoTex.loadTexture();
  twoTex.updatePixels();
}