createCanvas(400, 400);

  pixelDensity(1);

}

​

function draw() {

  background(220,200,0);

  fill(0,250,190);

  rect(30,20,80,100);

  circle(400,300,100);

  loadPixels();

  for(let i = 0; i<pixels.length; i++){//with image - img.pixels.length

    let p = i * 4;

    let r = pixels[p];

    let g = pixels[p+1];

    let b = pixels[p+2];

    let a = pixels[p+3];

    r = 50;

    pixels[p] = r;

    //when using images, use img.pixels

  }

  updatePixels();

  //console.log(pixels.length);

}