sm-01-getpixel-get.pde

PImage shapes;

void settings() {
  size(512, 512);
}

void setup() 
{
  shapes = loadImage("shapes.png");
}

void draw() 
{
  background(shapes);
  color c = shapes.get(mouseX, mouseY);
  fill(c);
  rect(mouseX - 25, mouseY - 25, 50, 50);
}

sm-01-getpixel-pixels.pde

PImage shapes;

void settings() {
  size(512, 512);
}

void setup() 
{
  shapes = loadImage("shapes.png");
  shapes.loadPixels();
}

void draw() 
{
  background(shapes);
  color c = shapes.pixels[mouseY * shapes.height + mouseX];
  fill(c);
  rect(mouseX - 25, mouseY - 25, 50, 50);
}

sm-01-getpixel-seq.pde

PImage shapes;

void settings() {
  size(512, 512);
}

void setup() 
{
  shapes = loadImage("shapes.png");
  shapes.loadPixels();
}

void draw() 
{
  int index = frameCount * 24;
  int x = index % shapes.width;
  int y = index / shapes.width;
    
  background(shapes);
  color c = shapes.pixels[index];
  fill(c);
  rect(x - 25, y - 25, 50, 50);
}