HTML5 Canvas鼠標與鍵盤事件 · HTML5 Canvas編程

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： ~~~ // 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.onmousedown = function(e){ } canvas.onmouseup = function(e){ } canvas.onmousemove = function(e){ } ~~~ **獲取鼠標在Canvas對象上坐標：** 由于Canvas上鼠標事件中不能直接獲取鼠標在Canvas的坐標，所獲取的都是基于整個屏幕的坐標。所以通過鼠標事件e.pageX與e.pageY來獲取鼠標位置，然后通過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： ~~~ 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 ~~~ <canvasid=*"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: ![](https://box.kancloud.cn/2016-05-17_573adb365c2a5.jpg) 一個完整的鼠標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> ~~~ **覺得不錯請支持一些，謝謝！！**