我们可以通过新的HTML5画布（Canvas）标签添加一个画布到网页中，以下代码用于定义一个 800 x 600 大小的画布。
再通过以下 JavaScript 代码控制在画布中的绘图。
// 通过ID取画布元素
var mc = document.getElementById("MyCanvas");
var ctx = null;
var width = mc.width;
var height = mc.height;
var mouseX = 0;
var mouseY = 0;
var pmouseX = 0;
var pmouseY = 0;
var drawRate = 6;
var frameCount = 0;
var mousePressed = false;
var PI = Math.PI;
var TWO_PI = Math.PI * 2;
var HALF_PI = Math.PI * 0.5;
var worms;
var colors = [];
colors[0] = '#2cd9fe';
colors[1] = '#2cfecf';
colors[2] = '#373fdf';
colors[3] = '#88fe1f';
colors[4] = '#48d6ff';
colors[5] = '#b3fcff';
colors[6] = '#f76cad';
colors[7] = '#505083';
colors[8] = '#113a7e';
colors[9] = '#014050';
colors[10] = '#ccf3ef';
colors[11] = '#009437';
colors[12] = '#8fb300';
if(mc.getContext)
{
// 创建 context 对象
ctx = mc.getContext("2d");
// 鼠标移动事件
mc.addEventListener('mousemove', ev_mousemove, false);
mc.addEventListener('mousedown', ev_mousedown, false);
mc.addEventListener('mouseup', ev_mouseup, false);
worms = new Array();
drawInternal();
}
function ev_mousemove(ev)
{
if (ev.layerX || ev.layerX == 0)
{
// 在Firefox中取鼠标坐标
mouseX = ev.layerX;
mouseY = ev.layerY;
}
else if (ev.offsetX || ev.offsetX == 0)
{
// 在Opera中取鼠标坐标
mouseX = ev.offsetX;
mouseY = ev.offsetY;
}
}
function ev_mousedown(ev)
{
mousePressed = true;
}
function ev_mouseup(ev)
{
mousePressed = false;
}
function drawInternal()
{
draw();
setTimeout('drawInternal()', drawRate);
pmouseX = mouseX;
pmouseY = mouseY;
frameCount++;
}
// 清画布
function clear()
{
ctx.clearRect(0, 0, width, height);
}
// 圆形填充
function fillCircle(x, y, radius)
{
if(radius <= 0)
radius = 0;
ctx.beginPath();
ctx.arc(x, y, radius, 0, TWO_PI, true);
ctx.closePath();
ctx.fill();
}
// 伪随机数
function Marsaglia(i1, i2)
{
var z=i1 || 362436069, w= i2 || 521288629;
var nextInt = function()
{
z=(36969*(z&65535)+(z >> 16)) & 0xFFFFFFFF;
w=(18000*(w&65535)+(w >> 16)) & 0xFFFFFFFF;
return (((z&0xFFFF) << 16) | (w&0xFFFF)) & 0xFFFFFFFF;
};
this.nextDouble = function()
{
var i = nextInt() / 4294967296;
return i < 0 ? 1 + i : i;
};
this.nextInt = nextInt;
}
Marsaglia.createRandomized = function()
{
var now = new Date();
return new Marsaglia((now / 60000) & 0xFFFFFFFF, now & 0xFFFFFFFF);
};
// Perlin Noise(由Ken Perlin发明的自然噪声生成算法)
function PerlinNoise(seed)
{
var rnd = seed != undefined ? new Marsaglia(seed) : Marsaglia.createRandomized();
var i, j;
var p = new Array(512);
for(i=0;i < 256;++i)
{
p[i] = i;
}
for(i=0;i < 256;++i)
{
var t = p[j = rnd.nextInt() & 0xFF];
p[j] = p[i];
p[i] = t;
}
for(i=0;i < 256;++i)
{
p[i + 256] = p[i];
}
function grad3d(i,x,y,z)
{
var h = i & 15;
var u = h < 8 ? x : y, v = h < 4 ? y : h == 12||h == 14 ? x : z;
return ((h&1) == 0 ? u : -u) + ((h&2) == 0 ? v : -v);
}
function grad2d(i,x,y)
{
var v = (i & 1) == 0 ? x : y;
return (i&2) == 0 ? -v : v;
}
function grad1d(i,x)
{
return (i&1) == 0 ? -x : x;
}
function lerp(t,a,b)
{
return a + t * (b - a);
}
this.noise3d = function(x, y, z)
{
var X = Math.floor(x)&255, Y = Math.floor(y)&255, Z = Math.floor(z)&255;
x -= Math.floor(x); y -= Math.floor(y); z -= Math.floor(z);
var fx = (3-2*x)*x*x, fy = (3-2*y)*y*y, fz = (3-2*z)*z*z;
var p0 = p[X]+Y, p00 = p[p0] + Z, p01 = p[p0 + 1] + Z,
p1 = p[X + 1] + Y, p10 = p[p1] + Z, p11 = p[p1 + 1] + Z;
return lerp(fz,
lerp(fy, lerp(fx, grad3d(p[p00], x, y, z), grad3d(p[p10], x-1, y, z)),
lerp(fx, grad3d(p[p01], x, y-1, z), grad3d(p[p11], x-1, y-1,z))),
lerp(fy, lerp(fx, grad3d(p[p00 + 1], x, y, z-1), grad3d(p[p10 + 1], x-1, y, z-1)),
lerp(fx, grad3d(p[p01 + 1], x, y-1, z-1), grad3d(p[p11 + 1], x-1, y-1,z-1))));
};
this.noise2d = function(x, y)
{
var X = Math.floor(x)&255, Y = Math.floor(y)&255;
x -= Math.floor(x); y -= Math.floor(y);
var fx = (3-2*x)*x*x, fy = (3-2*y)*y*y;
var p0 = p[X]+Y, p1 = p[X + 1] + Y;
return lerp(fy,
lerp(fx, grad2d(p[p0], x, y), grad2d(p[p1], x-1, y)),
lerp(fx, grad2d(p[p0 + 1], x, y-1), grad2d(p[p1 + 1], x-1, y-1)));
};
this.noise1d = function(x)
{
var X = Math.floor(x)&255;
x -= Math.floor(x);
var fx = (3-2*x)*x*x;
return lerp(fx, grad1d(p[X], x), grad1d(p[X+1], x-1));
};
}
var noiseProfile = { generator: undefined, octaves: 4, fallout: 0.5, seed: undefined};
function noise(x, y, z)
{
if(noiseProfile.generator == undefined)
{
noiseProfile.generator = new PerlinNoise(noiseProfile.seed);
}
var generator = noiseProfile.generator;
var t=1, k=1, sum=0;
for(var i=0;i < noiseProfile.octaves;++i)
{
t *= noiseProfile.fallout;
switch(arguments.length)
{
case 1:
sum += t * (1 + generator.noise1d(k*x)) / 2;
break;
case 2:
sum += t * (1 + generator.noise2d(k*x, k*y)) / 2;
break;
case 3:
sum += t * (1 + generator.noise3d(k*x, k*y, k*z)) / 2;
break;
}
k *= 2;
}
return sum;
}
function Worm(x,y)
{
this.x = x;
this.y = y;
this.lx = x;
this.ly = y;
this.heading = Math.sin(frameCount*0.083) * PI;;
this.rotation = Math.random() * (PI / (Math.random() * 70));
this.rate = 0;
this.maxLength = 15 + (noise(frameCount * 0.0025, frameCount*0.1) * 15);
this.detail = 2;
this.thickness = 3;
this.thicknessTarget = 5 + Math.random() * 10;
var cIndex = parseInt( Math.random() * colors.length );
this.c = colors[cIndex];
this.life = 30 + Math.random() * 120;
this.segments = new Array();
this.ooo = true;
this.counter = noise(frameCount * 0.1, frameCount*.1);
this.update = function()
{
this.life--;
if(this.life > 0)
{
this.thickness += (this.thicknessTarget-this.thickness) * 0.1;
this.thickness += 0.1;
if(this.thickness > this.thicknessTarget)
this.thickness = this.thicknessTarget;
this.heading += this.rotation;
this.rate = Math.cos( this.counter / 200.0) * (10 + noise(frameCount*0.05) * 10);
this.rotation = Math.sin(this.counter/this.rate) * (this.segments.length+1) * 0.010;
this.counter++;
var speedMod = (this.segments.length * this.segments.length * this.segments.length)
* 0.0015 * this.thickness / this.thicknessTarget;
var totalSpeed = (this.detail + speedMod);
var nx = Math.cos(this.heading) * totalSpeed;
var ny = Math.sin(this.heading) * totalSpeed;
this.walk(nx,ny);
}
else
{
if(this.segments.length > 1)
{
this.segments.pop();
}
else
{
this.thickness *= 0.95;
this.thickness -= 0.2;
if(this.thickness < 0.1)
this.ooo = true;
return;
}
}
this.ooo = true;
for(var i=0;i < this.segments.length;i++)
{
var segment = this.segments[i];
if(segment.ooo() == false)
{
this.ooo = false;
break;
}
}
}
this.walk = function(nx,ny)
{
this.lx = this.x;
this.ly = this.y;
this.x += nx;
this.y += ny;
var newSegment = new Segment(this.lx,this.ly,this.x,this.y,this.thickness);
this.segments.unshift(newSegment);
if(this.segments.length > 1)
{
this.segments[this.segments.length-1].smoothAgainst(this.segments[this.segments.length-2]);
}
if(this.segments.length >= this.maxLength)
{
this.segments.pop();
}
}
}
function Segment(x1,y1,x2,y2,thickness)
{
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
this.thickness = thickness;
var angle = Math.atan2(y2-y1,x2-x1);
this.lAngle = angle - HALF_PI;
var lDeltaX = Math.cos(this.lAngle) * thickness;
var lDeltaY = Math.sin(this.lAngle) * thickness;
this.leftX1 = x1 + lDeltaX;
this.leftY1 = y1 + lDeltaY;
this.leftX2 = x2 + lDeltaX;
this.leftY2 = y2 + lDeltaY;
this.rAngle = angle + HALF_PI;
var rDeltaX = Math.cos(this.rAngle) * thickness;
var rDeltaY = Math.sin(this.rAngle) * thickness;
this.rightX1 = x1 + rDeltaX;
this.rightY1 = y1 + rDeltaY;
this.rightX2 = x2 + rDeltaX;
this.rightY2 = y2 + rDeltaY;
this.smoothAgainst = function(last)
{
this.leftX1 = last.leftX2 = (last.leftX2 + this.leftX1) * 0.5;
this.leftY1 = last.leftY2 = (last.leftY2 + this.leftY1) * 0.5;
this.rightX1 = last.rightX2 = (last.rightX2 + this.rightX1) * 0.5;
this.rightY1 = last.rightY2 = (last.rightY2 + this.rightY1) * 0.5;
}
this.ooo = function()
{
if(this.x1 < 0 || this.y1 < 0 || this.x1 > width || this.y1 > height ||
this.x2 < 0 || this.y2 < 0 || this.x2 > width || this.y2 > height)
return true;
else
return false;
}
}
function draw()
{
clear();
for(var w=0; w < worms.length; w++)
{
var worm = worms[w];
worm.update();
ctx.fillStyle = worm.c;
ctx.lineWidth = 2;
ctx.strokeStyle = '#FFFFFF';
if(worm.segments.length>1)
{
ctx.beginPath();
ctx.moveTo(worm.segments[0].leftX1, worm.segments[0].leftY1);
for(var i=0; i < worm.segments.length; i++)
{
var segment = worm.segments[i];
ctx.lineTo(segment.leftX1,segment.leftY1);
}
ctx.lineTo(worm.segments[worm.segments.length-1].rightX1,
worm.segments[worm.segments.length-1].rightY1);
for(var i=worm.segments.length-1; i >= 0; i--)
{
var segment = worm.segments[i];
ctx.lineTo(segment.rightX1,segment.rightY1);
}
ctx.closePath();
ctx.fill();
ctx.stroke();
}
if(worm.segments.length>=1)
{
var x = worm.segments[0].x1;
var y = worm.segments[0].y1;
var thickness = worm.segments[0].thickness;
if(worm.thickness < thickness)
thickness = worm.thickness;
if(thickness <= 0)
thickness = 0.000001;
ctx.beginPath();
ctx.arc(x, y, thickness, worm.segments[0].lAngle, worm.segments[0].rAngle, false);
ctx.closePath();
ctx.stroke();
var xEnd = worm.segments[worm.segments.length-1].x1;
var yEnd = worm.segments[worm.segments.length-1].y1;
thickness = worm.segments[worm.segments.length-1].thickness;
if(worm.thickness < thickness)
thickness = worm.thickness;
if(thickness <= 0)
thickness = 0.000001;
ctx.beginPath();
ctx.arc(xEnd, yEnd, thickness, worm.segments[worm.segments.length-1].lAngle,
worm.segments[worm.segments.length-1].rAngle, true);
ctx.closePath();
ctx.stroke();
thickness = worm.thickness-0.6;
if(worm.thickness < thickness)
thickness = worm.thickness;
fillCircle(worm.segments[0].x1,worm.segments[0].y1,thickness);
thickness = worm.segments[worm.segments.length-1].thickness-0.6;
if(worm.thickness < thickness)
thickness = worm.thickness;
fillCircle(worm.segments[worm.segments.length-1].x1,
worm.segments[worm.segments.length-1].y1,thickness);
if(worm.life > 0)
{
ctx.fillStyle = "#FFFFFF";
fillCircle(worm.segments[0].x1,worm.segments[0].y1,thickness * 0.72);
}
}
}
for(var w=0; w < worms.length; w++)
{
var worm = worms[w];
if(worm.ooo)
{
worms.splice(w,1);
w--;
}
}
if(frameCount %2 ==0 && mousePressed && worms.length < 50)
{
var direction = Math.atan2(pmouseY-mouseY, pmouseX-mouseX) + PI;
var newWorm = new Worm(mouseX,mouseY);
worms.push( newWorm );
if(mouseX != pmouseX && mouseY != pmouseY)
{
newWorm.heading = direction;
}
}
}