#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;
