let imageToGrain;

​

function preload() {

  grainShader = loadShader("grain.vert", "grain.frag");

}

​

function setup() {

  createCanvas(400, 400, WEBGL);

  pixelDensity(5);

  // Just create an image to pass into the shader

  // This is just grey, but will be your artwork

  imageToGrain = createGraphics(width, height);

  imageToGrain.pixelDensity(pixelDensity());

  imageToGrain.background(127);

  // Set the image into the shader memory

  shader(grainShader);

  grainShader.setUniform("image", imageToGrain);

  grainShader.setUniform("pixD", pixelDensity());

  grainShader.setUniform("seed", random(100));

}

​

function draw() {

  // Update how much variance in the grain based on mouse x pos

  grainShader.setUniform("grainVary", mouseX/width);

  // Draw geometry to use the shader

  rect(-width/2, height/2, width, height);

}