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：

Full 360 degree View

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);

}

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