canvas 手写毛笔字效果

#canvasId {

background-color: #FFFFcc;

}

function Handwriting(id) {

this.canvas = document.getElementById(id);

this.ctx = this.canvas.getContext("2d");

this.ctx.fillStyle = "rgba(0,0,0,0.25)";

var _this = this;

this.canvas.onmousedown = function (e) { _this.downEvent(e)};

this.canvas.onmousemove = function (e) { _this.moveEvent(e)};

this.canvas.onmouseup = function (e) { _this.upEvent(e)};

this.canvas.onmouseout = function (e) { _this.upEvent(e)};

this.moveFlag = false;

this.upof = {};

this.radius = 0;

this.has = [];

this.lineMax = 30;

this.lineMin = 3;

this.linePressure = 1;

this.smoothness = 80;

}

Handwriting.prototype.clear = function () {

this.ctx.clearRect(0,0,this.canvas.width,this.canvas.height);

}

Handwriting.prototype.downEvent = function (e) {

this.moveFlag = true;

this.has = [];

this.upof = this.getXY(e);

}

Handwriting.prototype.moveEvent = function (e) {

if (!this.moveFlag)

return;

var of = this.getXY(e);

var up = this.upof;

var ur = this.radius;

this.has.unshift({time:new Date().getTime() ,dis:this.distance(up,of)});

var dis = 0;

var time = 0;

for (var n = 0; n < this.has.length-1; n++) {

dis += this.has[n].dis;

time += this.has[n].time-this.has[n+1].time;

if (dis>this.smoothness)

break;

}

var or = Math.min(time/dis*this.linePressure+this.lineMin , this.lineMax) / 2;

this.radius = or;

this.upof = of;

if (this.has.length<=4)

return;

var len = Math.round(this.has[0].dis/2)+1;

for (var i = 0; i < len; i++) {

var x = up.x + (of.x-up.x)/len*i;

var y = up.y + (of.y-up.y)/len*i;

var r = ur + (or-ur)/len*i;

this.ctx.beginPath();

this.ctx.arc(x,y,r,0,2*Math.PI,true);

this.ctx.fill();

}

}

Handwriting.prototype.upEvent = function (e) {

this.moveFlag = false;

}

Handwriting.prototype.getXY = function (e)

{

return {

x : e.clientX - this.canvas.offsetLeft + (document.body.scrollLeft || document.documentElement.scrollLeft),

y : e.clientY - this.canvas.offsetTop + (document.body.scrollTop || document.documentElement.scrollTop)

}

}

Handwriting.prototype.distance = function (a,b)

{

var x = b.x-a.x , y = b.y-a.y;

return Math.sqrt(x*x+y*y);

}

var hw = new Handwriting("canvasId");

hw.lineMax = 40;

hw.lineMin = 5;

hw.linePressure = 2.5;

hw.smoothness = 100;