import processing.opengl.*;
import javax.media.opengl.*;
PImage img;

void setup() {
  size(600,600, OPENGL);
    
  img = createImage(10, 10, RGB);
  
  float md = 0.5*sqrt(sq(img.width/2)+sq(img.height/2));
  for (int x = 0; x < img.width; x++) {
    for (int y = 0; y < img.height; y++) {
      float d = sqrt(sq(x-img.width/2)+sq(y-img.height/2));
      img.set(x ,y , color(0, 128-128*d/md, 0));
    }  
  }

}

void draw() 
{
  /* Three images plotted:
     all 100x100 px WxH 
     at: 
     (0, 0)
     (25, 25)
     (50, 50)
     (75, 75)
  */
     
  background(0);
  // image "A" -- smaller
  blend(img,
        0, 0, 
        img.width, img.height,
        0, 0,  //x & y of new image
        100, 100,  //width & height of new image
        ADD);

  // image "B" - larger
  blend(img,
        0, 0, 
        img.width, img.height,
        25, 25,  //x & y of new image
        100, 100,  //width & height of new image
        ADD);

  blend(img,
        0, 0, 
        img.width, img.height,
        50, 50,  //x & y of new image
        100, 100,  //width & height of new image
        ADD);

  blend(img,
        0, 0, 
        img.width, img.height,
        75, 75,  //x & y of new image
        100, 100,  //width & height of new image
        ADD); 
}