MoireDecoder.pde

int frame = 0;
int wallOffset = 0;

final int windowWidth = 1;
final int wallWidth = 4;
boolean isDrawWallEnabled = false;
boolean isWallAnimated = true;
PImage pattern;

void setup() {
  size(500, 500);
  frameRate(60);


  // use pgraphics instead
  // create and set the patter accumulator to white
  pattern = createImage(width, height, RGB);
  for (int i = 0; i < pattern.pixels.length; i++) {
    pattern.pixels[i] = color(255);
  }
  pattern.updatePixels();
}

void draw() {
  background(255);

  // sample
  if (frame < width) {
    // draw a frame of animation
    fill(0);    
    noStroke();
    ellipse((float)frame * 3, (float)frame * 3, 50.0, 50.0);

    // copy relevant slices of frame into pattern accumulation image
    int windowOffset = frameCount % (wallWidth + windowWidth);
    for (int x = windowOffset; x < width; x += wallWidth + windowWidth) {
      for (int i = 0; i < windowWidth; i++) {
        int windowX = x + i;

        for (int y = 0; y < height; y++) {
          // dumb darkest blend
          color baseColor = pattern.get(windowX, y);
          color newColor = get(windowX, y);
          pattern.set(windowX, y, color(min(red(newColor), red(baseColor)), min(green(newColor), green(baseColor)), min(blue(newColor), blue(baseColor))));
        }
      }
    }
  } else {
    // draw the image when we are done sampling
    image(pattern, 0, 0);
  }

  // decoder
  if (isDrawWallEnabled) {
    for (int i = (wallOffset % wallWidth) - wallOffset; i < width; i += wallWidth + windowWidth) {
      fill(0);
      noStroke();
      rect(i, 0, wallWidth, height);
    }
  }

  if (isWallAnimated) {
    wallOffset += windowWidth;
  }

  frame += wallWidth;
}

void keyPressed() {
  if (keyCode == RIGHT) {
    wallOffset++;
  } else if (keyCode == LEFT) {
    wallOffset--;
  } else if (key == ' ') {
    isDrawWallEnabled = !isDrawWallEnabled;
  } else if (key == 'a') {
    isWallAnimated = !isWallAnimated;
  }
}