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演示Html5 Canvas鼠標事件，獲取Canvas對象上的鼠標坐標，演示鍵盤事件通過鍵盤控制Canvas上對象移動。 

Canvas對象支持所有的JavaScript的鼠標事件，包括鼠標點擊(MouseClick), 鼠標按下(Mouse Down), 鼠標抬起(Mouse Up),鼠標移動( Mouse Move)對Canvas添加鼠標事件方式有兩種，一種方式是通過API來完成： 

 

復制代碼代碼如下:
// mouse event 
canvas.addEventListener("mousedown",doMouseDown,false); 
canvas.addEventListener('mousemove', doMouseMove,false); 
canvas.addEventListener('mouseup', doMouseUp, false); 
另外一種方式在JavaScript中稱為反模式：
 

 

復制代碼代碼如下:
canvas.onmousedown = function(e){ 
} 
canvas.onmouseup = function(e){ 
} 
canvas.onmousemove = function(e){ 
} 
 

獲取鼠標在Canvas對象上坐標： 
由於Canvas上鼠標事件中不能直接獲取鼠標在Canvas的坐標，所獲取的都是基於整個 
屏幕的坐標。所以通過鼠標事件e.pageX與e.pageY來獲取鼠標位置，然後通過 
Canvas. getBoundingClIEntRect()來獲取Canvas對象相對屏幕的相對位置，通過計算 

得到鼠標在Canvas的坐標，代碼如下： 

 

復制代碼代碼如下:
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) 
}; 
} 
 

鍵盤事件： 
Html5 Canvas本身不支持鍵盤事件監聽與獲取，常用的有兩種方法來解決這個問題： 

一：通過Windows對象來實現Canvas鍵盤事件監聽與處理 
// key event - use window as object 
window.addEventListener('keydown', doKeyDown,true); 

二：通過在Canvas對象上添加其它支持鍵盤事件的DOM元素實現鍵盤事件支持 

 

復制代碼代碼如下:
<canvas id="event_canvas"tabindex="0"></canvas> 
// key event - use DOM element asobject 
canvas.addEventListener('keydown', doKeyDown,true); 
canvas.focus(); 
 

其中tabindex為Html5 DOM元素，支持鍵盤事件。 
演示，一個可以根據鍵盤上下左右移動的矩形塊: 
 
一個完整的鼠標與鍵盤事件演示代碼如下： 

 

復制代碼代碼如下:
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： 

 

復制代碼代碼如下:
<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>