​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  fill(x, x, x);

  rect(0, 0, width, height);

  // Slider frame

  fill(0);

  stroke(0);

  strokeWeight(1);  

  rect(75, 200, 240, 30, 20);

    // Slider move

  noStroke(); 

  fill(300);

  rect(75, 200, x, 30, 20);

  // When mouse is pressed, move with mouse x

  if (mouseIsPressed === true) {

    x = constrain(mouseX - 50, 50, 250);

  }

}

​