HTML5 Canvas鼠标与键盘事件

简介: HTML5 Canvas鼠标与键盘事件

演示HTML5 Canvas鼠标事件,获取Canvas对象上的鼠标坐标,演示键盘事件

通过键盘控制Canvas上对象移动。


Canvas对象支持所有的JavaScript的鼠标事件,包括鼠标点击(MouseClick), 鼠标按下


(Mouse Down), 鼠标抬起(Mouse Up),鼠标移动( Mouse Move)


对Canvas添加鼠标事件方式有两种,一种方式是通过API来完成:


// mouse event


canvas.addEventListener("mousedown",doMouseDown,false);


canvas.addEventListener('mousemove', doMouseMove,false);


canvas.addEventListener('mouseup',  doMouseUp, false);


另外一种方式在JavaScript中称为反模式:


canvas.onmousedown = function(e){


 


}


canvas.onmouseup = function(e){


 


}


canvas.onmousemove = function(e){


 


}


获取鼠标在Canvas对象上坐标:


由于Canvas上鼠标事件中不能直接获取鼠标在Canvas的坐标,所获取的都是基于整个


屏幕的坐标。所以通过鼠标事件e.pageX与e.pageY来获取鼠标位置,然后通过


Canvas. getBoundingClientRect()来获取Canvas对象相对屏幕的相对位置,通过计算


得到鼠标在Canvas的坐标,代码如下:


function getPointOnCanvas(canvas, x, y) {


   var bbox =canvas.getBoundingClientRect();


   return { x: x- bbox.left *(canvas.width / bbox.width),


           y:y - bbox.top  * (canvas.height / bbox.height)


           };


}


键盘事件:


HTML5 Canvas本身不支持键盘事件监听与获取,常用的有两种方法来解决这个问题:


一:通过windows对象来实现Canvas键盘事件监听与处理

// key event - use window as object


window.addEventListener('keydown', doKeyDown,true);


二:通过在Canvas对象上添加其它支持键盘事件的DOM元素实现键盘事件支持


<canvas id="event_canvas"tabindex="0"></canvas>


// key event - use DOM element asobject


canvas.addEventListener('keydown', doKeyDown,true);


canvas.focus();


其中tabindex为HTML5 DOM元素,支持键盘事件。


演示,一个可以根据键盘上下左右移动的矩形块:


一个完整的鼠标与键盘事件演示代码如下:

    var tempContext = null; // global variable 2d context
    var started = false;
    var mText_canvas = null;
    var x = 0, y =0;
    window.add
    window.onload = function() {
      var canvas = document.getElementById("event_canvas");
      console.log(canvas.parentNode.clientWidth);
      canvas.width = canvas.parentNode.clientWidth;
      canvas.height = canvas.parentNode.clientHeight;
      
      if (!canvas.getContext) {
          console.log("Canvas not supported. Please install a HTML5 compatible browser.");
          return;
      }
      
      // get 2D context of canvas and draw rectangel
      tempContext = canvas.getContext("2d");
      tempContext.fillStyle="blue";
      x = canvas.width/2;
      y = canvas.height/2;
      tempContext.fillRect(x, y, 80, 40);
  
          // key event - use DOM element as object
          canvas.addEventListener('keydown', doKeyDown, true);
          canvas.focus();  
          // key event - use window as object
          window.addEventListener('keydown', doKeyDown, true);
          
          // mouse event
          canvas.addEventListener("mousedown", doMouseDown, false);
          canvas.addEventListener('mousemove', doMouseMove, false);
          canvas.addEventListener('mouseup',   doMouseUp, false);
    }
    
    function getPointOnCanvas(canvas, x, y) {
      var bbox = canvas.getBoundingClientRect();
      return { x: x - bbox.left * (canvas.width  / bbox.width),
          y: y - bbox.top  * (canvas.height / bbox.height)
          };
    }
    
    function doKeyDown(e) {
      var keyID = e.keyCode ? e.keyCode :e.which;
      if(keyID === 38 || keyID === 87)  { // up arrow and W
        clearCanvas();
        y = y - 10;
        tempContext.fillRect(x, y, 80, 40);
        e.preventDefault();
      }
      if(keyID === 39 || keyID === 68)  { // right arrow and D
        clearCanvas();
        x = x + 10;
        tempContext.fillRect(x, y, 80, 40);
        e.preventDefault();
      }
      if(keyID === 40 || keyID === 83)  { // down arrow and S
        clearCanvas();
        y = y + 10;
        tempContext.fillRect(x, y, 80, 40);
        e.preventDefault();
      }
      if(keyID === 37 || keyID === 65)  { // left arrow and A
        clearCanvas();
        x = x - 10;
        tempContext.fillRect(x, y, 80, 40);
        e.preventDefault();
      }
    }
    
    function clearCanvas() {
      tempContext.clearRect(0, 0, 500, 500)
    }
    
    function doMouseDown(event) {
      var x = event.pageX;
      var y = event.pageY;
      var canvas = event.target;
      var loc = getPointOnCanvas(canvas, x, y);
      console.log("mouse down at point( x:" + loc.x + ", y:" + loc.y + ")");
      tempContext.beginPath();
      tempContext.moveTo(loc.x, loc.y);
      started = true;
    }
    
    function doMouseMove(event) {
      var x = event.pageX;
      var y = event.pageY;
      var canvas = event.target;
      var loc = getPointOnCanvas(canvas, x, y);
      if (started) {
        tempContext.lineTo(loc.x, loc.y);
        tempContext.stroke();
      }
    }
    
    function doMouseUp(event) {
      console.log("mouse up now");
        if (started) {
          doMouseMove(event);
            started = false;
      }
    }

HTML部分:

<body>
  <h1>HTML Canvas Event Demo - By Gloomy Fish</h1>
  <pre>Press W, A, S, D keys to move</pre>
  <div id="my_painter">
    <canvas id="event_canvas" tabindex="0"></canvas>
  </div>
</body>

觉得不错请支持一些,谢谢!!

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