Question

我需要为我正在处理的画布应用程序添加触摸功能（多个用户白板），我已经阅读了有关事件监听器和event.preventDefault()，但我无法理解我可以使用'DOMContentLoaded'和'touchmove'两个事件监听器。此时我不知道使用多个事件监听器是否是我需要的解决方案。

这是我正在使用的代码：

document.addEventListener("DOMContentLoaded", function() {

   var mouse = { 
      click: false,
      move: false,
      pos: {x:0, y:0},
      pos_prev: false
   };

   var canvas  = document.getElementById('drawing');
   var context = canvas.getContext('2d');
   var width   = 1280;
   var height  = 960;
   var socket  = io.connect();
   var lineWidth = 1;
   var shadowBlur = 1;
   var shadowColor = "black";
   var strokeStyle = "black";

   canvas.width = width;
   canvas.height = height;

   canvas.onmousedown = function(e){ mouse.click = true; };
   canvas.onmouseup = function(e){ mouse.click = false; };

   canvas.onmousemove = function(e) {
      mouse.pos.x = e.clientX / width;
      mouse.pos.y = e.clientY / height;
      mouse.move = true;
   };

    socket.on('draw_line', function (data) {
       var line = data.line;
       context.beginPath();
       context.lineWidth = lineWidth;
       context.shadowBlur = shadowBlur;
       context.strokeStyle = strokeStyle;
       context.lineJoin="round";
       context.lineCap = "round";
       context.moveTo(line[0].x * width, line[0].y * height);
       context.lineTo(line[1].x * width, line[1].y * height);
       context.stroke();
   });

   function mainLoop() {
      if (mouse.click && mouse.move && mouse.pos_prev) {
         socket.emit('draw_line', { line: [ mouse.pos, mouse.pos_prev ] });
         mouse.move = false;
      }
      mouse.pos_prev = {x: mouse.pos.x, y: mouse.pos.y};
      setTimeout(mainLoop, 50);
   }
   mainLoop();
});

我真的很感激任何帮助。

感谢。

Answer 1

你遇到某种错误吗？现在，您的代码似乎通过侦听单击鼠标并移动鼠标来进行操作。如果按下鼠标，则移动鼠标并且循环至少运行一次（mouse.click＆amp;＆amp; mouse.move＆amp;＆amp; mouse.pos_prev）然后它在canvas元素上绘制一条线。 / p>

JavaScript Canvas使用多个eventListeners触摸未来

1 个答案: