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！！
