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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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原文地址：https://www.cnblogs.com/shihaiming/p/6278225.html