HTML5 Canvas鼠标与键盘事件demo示例_HTML5_网页制作_IT 经验

本文的主要母的是演示HTML5Canvas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，感兴趣的朋友可以参考下哈，希望对大家有所帮助

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>