HTML5 Canvas实现360度全景图

原文：http://blog.csdn.net/jia20003/article/details/17172571

很多购物网站现在都支持360实物全景图像，可以360度任意选择查看样品，这样

对购买者来说是一个很好的消费体验，网上有很多这样的插件都是基于jQuery实现的

有收费的也有免费的，其实很好用的一个叫3deye.js的插件。该插件支持桌面与移动终

端iOS与Android，它的demo程序：http://www.voidcanvas.com/demo/28823deye/

自己玩了玩这个Demo以后，照着它的思路，用HTML5 Canvas也实现了类似的功能。

所以先说一下它的360度全景图的原理

1. 首先需要对实物拍照，间隔是每张照片旋转15度，所以需要23张照片。

2. 照片准备好了以后，尽量选择JPG格式，裁剪到适当大小。

3. JavaScript中预加载所有照片，可以配合进度条显示加载精度

4. 创建/获取Canvas对象，加上鼠标监听事件，当鼠标左右移动时候，适度的绘制不

同帧。大致的原理就是这样，简单吧！

实现代码：

<!DOCTYPE html>

<html>

<head>

  <meta charset=utf-8">

  <title>Full 360 degree View</title>

  <script>

        var ctx = null; // global variable 2d context

        var frame = 1; // 23

        var width = 0;

        var height = 0;

        var started = false;

        var images = new Array();

        var startedX = -1;

      window.onload = function() {

        var canvas = document.getElementById("fullview_canvas");

        canvas.width = 440;// window.innerWidth;

        canvas.height = 691;//window.innerHeight;

        width = canvas.width;

        height = canvas.height;

        var bar = document.getElementById('loadProgressBar');

        for(var i=1; i<24; i++)

        {

            bar.value = i;

            if(i<10)

            {

                images[i] = new Image();

                images[i].src = "0" + i + ".jpg";

            }

            else

            {

                images[i] = new Image();

                images[i].src = i + ".jpg";

            }

        }

        ctx = canvas.getContext("2d");

        // mouse event

        canvas.addEventListener("mousedown", doMouseDown, false);

        canvas.addEventListener('mousemove', doMouseMove, false);

        canvas.addEventListener('mouseup',   doMouseUp, false);

        // loaded();

        // frame = 1

        frame = 1;

        images[frame].onload = function() {

            redraw();

            bar.style.display = 'none';

        }

    }

    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 + ")");

        startedX = loc.x;

        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) {

            var count = Math.floor(Math.abs((startedX - loc.x)/30));

            var frameIndex = Math.floor((startedX - loc.x)/30);

            while(count > 0)

            {

                console.log("frameIndex = " + frameIndex);

                count--;

                if(frameIndex > 0)

                {

                    frameIndex--;

                    frame++;

                } else if(frameIndex < 0)

                {

                    frameIndex++;

                    frame--;

                }

                else if(frameIndex == 0)

                {

                    break;

                }

                if(frame >= 24)

                {

                    frame = 1;

                }

                if(frame <= 0)

                {

                    frame = 23;

                }

                redraw();

            }

        }

    }

    function doMouseUp(event) {

        console.log("mouse up now");

        if (started) {

            doMouseMove(event);

            startedX = -1;

            started = 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 loaded() {

        setTimeout( update, 1000/8);

    }

    function redraw()

    {

        // var imageObj = document.createElement("img");

        // var imageObj = new Image();

        var imageObj = images[frame];

        ctx.clearRect(0, 0, width, height)

        ctx.drawImage(imageObj, 0, 0, width, height);

    }

    function update() {

        redraw();

        frame++;

        if (frame >= 23) frame = 1;

        setTimeout( update, 1000/8);

    }

  </script>

</head>

<body>

<progress id="loadProgressBar" value="0" max="23"></progress>

<canvas id="fullview_canvas"></canvas>

<button onclick="loaded()">Auto Play</button>

</body>

</html>

Demo演示文件下载地址->http://download.csdn.net/detail/jia20003/6670901

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HTML5 Canvas实现360度全景图

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