JavaScript

语言：

JaveScriptBabelCoffeeScript

确定

function g(e) {

return document.getElementById(e);

}

/* 一个插值算法 */

function Cubic(t, b, c, d) {

return c * (t /= d) * t * t + b;

}

var ctx = g('pad').getContext('2d');

ctx.scale(100, 100);

ctx.translate(3, 3);

var theta = 4.2; //转角

var eleva = 0.6; //仰角

/* 投影算法 */

function iso(x, y, z) {

var dist = Math.sqrt(x * x + y * y);

var angle = (x == 0 && y == 0) ? 0 : Math.atan(y / x) + theta + ((x < 0) ? Math.PI : 0);

x = Math.cos(angle) * dist;

y = -Math.sin(angle) * dist;

var fact = (y * Math.cos(eleva) + z * Math.sin(eleva) + 8) / 8;

y = y * Math.sin(eleva) - z * Math.cos(eleva);

x *= fact;

y *= fact;

return {

x: x,

y: y

};

}

/* 球方程 x^2+y^2+z^2=r^2 */

function sphere(r) {

var x, y, z;

var t;

z = -r;

while (z < r) {

x = -Math.sqrt(r * r - z * z);

y = 0;

t = 1;

co = iso(x, y, z);

ctx.moveTo(co.x, co.y);

while (true) {

y = Math.sqrt((r * r - x * x - z * z)) * t;

if (isNaN(y)) { /* 此时，x值为极值,y的绝对值已经不能再小 */

if (t == 1) {

t = -t;

x = Math.sqrt(r * r - z * z);

continue;

} /* x值达到最大 */

else break;

};

co = iso(x, y, z);

ctx.lineTo(co.x, co.y);

x += 0.1 * t;

}

ctx.closePath();

z = Cubic(1, z, 2 * r, 4); //应用插值算法(分布均匀些)

}

}

function preview() {

ctx.clearRect(-3, -3, 10, 10);

ctx.lineWidth = 0.001;

ctx.lineJoin = "round";

ctx.strokeStyle = 'rgba(0,0,100,0.8)';

var co;

ctx.beginPath();

sphere(2);

ctx.stroke();

}

preview();

/* 鼠标控制 */

g('pad').onmousedown = function(e) {

var x0 = e.clientX,

y0 = e.clientY;

document.onmousemove = function(e) {

theta -= (x0 - (x0 = e.clientX)) / 100;

eleva -= (y0 - (y0 = e.clientY)) / 100;

theta %= Math.PI * 2;

if (theta < 0) theta += Math.PI * 2;

eleva %= Math.PI * 2;

if (eleva < 0) eleva += Math.PI * 2;

preview();

}

document.onmouseup = function(e) {

document.onmousemove = null;

}

};