演示HTML5 Canvas鼠標(biāo)事件，獲取Canvas對(duì)象上的鼠標(biāo)坐標(biāo)，演示鍵盤事件
通過(guò)鍵盤控制Canvas上對(duì)象移動(dòng)。

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Canvas對(duì)象支持所有的JavaScript的鼠標(biāo)事件，包括鼠標(biāo)點(diǎn)擊(MouseClick), 鼠標(biāo)按下

(Mouse Down), 鼠標(biāo)抬起(Mouse Up),鼠標(biāo)移動(dòng)( Mouse Move)

對(duì)Canvas添加鼠標(biāo)事件方式有兩種，一種方式是通過(guò)API來(lái)完成：

// 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：

canvas. =function(e){

}

canvas. =function(e){

}

canvas. =function(e){

}

獲取鼠標(biāo)在Canvas對(duì)象上坐標(biāo)：

由于Canvas上鼠標(biāo)事件中不能直接獲取鼠標(biāo)在Canvas的坐標(biāo)，所獲取的都是基于整個(gè)

屏幕的坐標(biāo)。所以通過(guò)鼠標(biāo)事件e.pageX與e.pageY來(lái)獲取鼠標(biāo)位置，然后通過(guò)

Canvas. getBoundingClientRect()來(lái)獲取Canvas對(duì)象相對(duì)屏幕的相對(duì)位置，通過(guò)計(jì)算

得到鼠標(biāo)在Canvas的坐標(biāo)，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(jiān)聽(tīng)與獲取，常用的有兩種方法來(lái)解決這個(gè)問(wèn)題：

一：通過(guò)windows對(duì)象來(lái)實(shí)現(xiàn)Canvas鍵盤事件監(jiān)聽(tīng)與處理
// key event - use window as object

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

二：通過(guò)在Canvas對(duì)象上添加其它支持鍵盤事件的DOM元素實(shí)現(xiàn)鍵盤事件支持

"event_canvas"tabindex="0">

// 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(gè)可以根據(jù)鍵盤上下左右移動(dòng)的矩形塊:

一個(gè)完整的鼠標(biāo)與鍵盤事件演示代碼如下：

		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 Canvas Event Demo - By Gloomy Fish
 	
Press W, A, S, D keys to move