在html5的画布上，画出三维图形，并且实现它动态的围着一条轴进行旋转。

实现步骤：

1、定义一个对象Vector3，用于存储三维的坐标

2、定义一个观察点坐标和显示屏，初始化观察点的显示屏的距离(主要通过他们计算出各个点在二维平面的坐标值)

3、定义八个点(为了方便计算，我将会是画布和坐标进行i平移和旋转)

4、通过一定的公式，计算出八个点显示在平面的坐标(x,y)

5、使用moveTo和lineTo连接所有的直线

6、定义进行旋转的方法(难点，主要使用三维立体计算出各个点的推导公式)

7、最后进行旋转

3D图形(3D旋转)

body{margin: 0 0 0 0;padding: 0 0 0 0;}

//定义一个三维矢量类

Vector3 = function(x,y,z){

this.x = x;

this.y = y;

this.z = z;

}

//

var canvas = document.getElementById('mc');

var cxt = canvas.getContext('2d');

//定义一些常量，用于以后使用

var currentAngle = 0;

var translateX = 300;

var translateY = 300;

var points = [];

var distance = 500;//定义摄像机和摄像机距离显示屏的距离

var eyePosition = new Vector3(0,0,700);//定义眼睛所在的位置

cxt.translate(translateX,translateY);

cxt.scale(1,-1);//是的y的方向相反

//初始化八个顶点

function init_eight_points(){

//z轴上面的四个点

points[0] = new Vector3(100,100,100);

points[1] = new Vector3(100,-100,100);

points[2] = new Vector3(-100,-100,100);

points[3] = new Vector3(-100,100,100);

//下面四个点

points[4] = new Vector3(100,100,-100);

points[5] = new Vector3(100,-100,-100);

points[6] = new Vector3(-100,-100,-100);

points[7] = new Vector3(-100,100,-100);

}

//8个顶点、摄像机、摄像机到显示屏的距离都已经有了。就可以开始计算八个顶点到显示屏上面的x、y坐标了

//projection 投射、发射、推测

function chang_projection(){

for(var i = 0 ;i < points.length ; i++){

points[i].x = points[i].x * distance / Math.abs(eyePosition.z - points[i].z);

points[i].y = points[i].y * distance / Math.abs(eyePosition.z - points[i].z);

}

}

//已经计算出来了所有点的坐标，接下来就是把所有的点的坐标连接起来就行

function drawCube(){

//画出下面的八条虚线

cxt.strokeStyle = "#0FF595";

cxt.lineWidth = 2;

cxt.beginPath();

cxt.moveTo(points[4].x,points[4].y);

cxt.lineTo(points[5].x,points[5].y);

cxt.lineTo(points[6].x,points[6].y);

cxt.lineTo(points[7].x,points[7].y);

cxt.lineTo(points[4].x,points[4].y);

cxt.lineTo(points[0].x,points[0].y);

cxt.moveTo(points[5].x,points[5].y);

cxt.lineTo(points[1].x,points[1].y);

cxt.moveTo(points[6].x,points[6].y);

cxt.lineTo(points[2].x,points[2].y);

cxt.moveTo(points[7].x,points[7].y);

cxt.lineTo(points[3].x,points[3].y);

cxt.moveTo(points[0].x,points[0].y);

cxt.lineTo(points[1].x,points[1].y);

cxt.lineTo(points[2].x,points[2].y);

cxt.lineTo(points[3].x,points[3].y);

cxt.lineTo(points[0].x,points[0].y);

cxt.stroke();

}

//旋转计算坐标的方法 (沿着x轴旋转)

function rotate(angle){

//沿着x轴进行旋转

for (i = 0; i < points.length; i++) {

var tempY = points[i].y;

points[i].y = points[i].y * Math.cos(angle) - points[i].z * Math.sin(angle);

points[i].z = tempY * Math.sin(angle) + points[i].z * Math.cos(angle);

}

//沿着y轴进行旋转

for (var i = 0; i < points.length; i++) {

var tempX = points[i].x;

points[i].x = points[i].x * Math.cos(angle) - points[i].z * Math.sin(angle);

points[i].z = points[i].z * Math.cos(angle) + tempX * Math.sin(angle);

}

//沿着z轴进行旋转

for(var i = 0 ; i < points.length ; i++){

var tempX = points[i].x;

var tempY = points[i].y;

points[i].x = tempX * Math.cos(angle) - tempY * Math.sin(angle);

points[i].y = tempX * Math.sin(angle) + tempY * Math.cos(angle);

}

}

//计算角度的方法

function degToRad(a){

return a * Math.PI / 180;

}

//移动显示屏改变其三维投影的图形

var somethingAsync = eval(Jscex.compile("async", function () {

while (true) {

cxt.clearRect(-translateX,-translateY,canvas.width,canvas.height);//清除画布

init_eight_points();//初始化所有的点

rotate(degToRad(currentAngle));//旋转角度之后，计算所有的点坐标

currentAngle += 10;//每次以10°的频率旋转

chang_projection();//计算所有点在二维平面的上的坐标

drawCube();//画出所有的图形

$await(Jscex.Async.sleep(100));

}

}));

somethingAsync().start();