static/js/utils.js

class DrawingState {
  constructor(imageData) {
    this.imageData = imageData;
  }
}

function getMousePos(canvas, evt) {
  const rect = canvas.getBoundingClientRect();
  return {
    x: evt.clientX - rect.left,
    y: evt.clientY - rect.top
  };
}

function getTouchPos(canvas, evt) {
  const rect = canvas.getBoundingClientRect();
  return {
    x: evt.touches[0].clientX - rect.left,
    y: evt.touches[0].clientY - rect.top
  };
}