画布无法正确处理偏移的触摸事件

Question

嘿，所以我的触摸事件偏移量有问题，可以用鼠标在画布上绘制，但是用触摸板偏移量在角落很远，当我触摸画布时，它会“绘制”触摸板，但就像我说的那样。我知道我的偏移量不见了，但是我是一个JavaScript新手，并且一直在尝试调试几个小时

$( document ).ready(function() {

  var container = document.getElementById('canvas');
  init(container, 200, 200, '#ddd');


  function init(container, width, height, fillColor) {
    var canvas = createCanvas(container, width, height);
    var ctx = canvas.getContext('2d');


    var mouse = {x: 0, y: 0};
    var touch = {x: 0, y: 0};
    var last_mouse = {x: 0, y: 0};
    var last_touch = {x: 0, y: 0};


    canvas.addEventListener('mousemove', function(e) {
      last_mouse.x = mouse.x;
      last_mouse.y = mouse.y;


      if (e.offsetX) {
        mouse.x = e.offsetX;
        mouse.y = e.offsetY;
      }
    });    

    canvas.addEventListener('touchmove', function(e) {
      var touch = e.touches[0];
      last_touch.x = e.pageX - touch.offsetLeft;
      last_touch.y = e.pageY - touch.offsetTop;


      if (e.offsetX) {
        touch.x = e.offsetX;
        touch.y = e.offsetY;
      }
    });  

    canvas.onmousemove = function(e) {

      var x = e.pageX - this.offsetLeft;
      var y = e.pageY - this.offsetTop;
    };

    canvas.addEventListener('touchstart', function(e) {
      canvas.addEventListener('touchmove', onTouchPaint, false);
    }, false);

    canvas.addEventListener('mousedown', function(e) {
      canvas.addEventListener('mousemove', onPaint, false);
    }, false);
    canvas.addEventListener('mouseup', function() {
      canvas.removeEventListener('mousemove', onPaint, false);
    });

    var onPaint = function() {
      ctx.beginPath();
      ctx.moveTo(last_mouse.x, last_mouse.y);
      ctx.lineTo(mouse.x, mouse.y);
      ctx.closePath();
      ctx.stroke();

      ctx.lineWidth = 15 ;
      ctx.lineJoin = 'round';
      ctx.lineCap = 'round';
      ctx.strokeStyle = 'black';
    };

    var onTouchPaint = function() {
      ctx.beginPath();
      ctx.moveTo(last_touch.x, last_touch.y);
      ctx.lineTo(touch.x, touch.y);
      ctx.closePath();
      ctx.stroke();

      ctx.lineWidth = 15 ;
      ctx.lineJoin = 'round';
      ctx.lineCap = 'round';
      ctx.strokeStyle = 'black';
    };
  } 
});

要么是onTouchPaint要么是touchmove，这正在杀死我。任何帮助都可以申请。