贝塞尔曲线整理

<canvas id="myCanvas" width="500" height="500" style="border:1px solid red"></canvas>
<script type="text/javascript">
/*
参考维基百科
http://zh.wikipedia.org/wiki/%E8%B2%9D%E8%8C%B2%E6%9B%B2%E7%B7%9A
*/
function Point2D(x,y){
this.x=x||0.0;
this.y=y||0.0;
}
/*
cp在此是四個元素的陣列:
cp[0]為起始點，或上圖中的P0
cp[1]為第一個控制點，或上圖中的P1
cp[2]為第二個控制點，或上圖中的P2
cp[3]為結束點，或上圖中的P3
t為參數值，0 <= t <= 1
*/
function PointOnCubicBezier( cp, t )
{
var ax, bx, cx;
var ay, by, cy;
var tSquared, tCubed;
var result = new Point2D ;
/*計算多項式係數*/
cx = 3.0 * (cp[1].x - cp[0].x);

bx = 3.0 * (cp[2].x - cp[1].x) - cx;
ax = cp[3].x - cp[0].x - cx - bx;
cy = 3.0 * (cp[1].y - cp[0].y);
by = 3.0 * (cp[2].y - cp[1].y) - cy;
ay = cp[3].y - cp[0].y - cy - by;
/*計算位於參數值t的曲線點*/
tSquared = t * t;
tCubed = tSquared * t;
result.x = (ax * tCubed) + (bx * tSquared) + (cx * t) + cp[0].x;
result.y = (ay * tCubed) + (by * tSquared) + (cy * t) + cp[0].y;
return result;
}
/*
ComputeBezier以控制點cp所產生的曲線點，填入Point2D結構的陣列。
呼叫者必須分配足夠的記憶體以供輸出結果，其為<sizeof(Point2D) numberOfPoints>
*/
function ComputeBezier( cp, numberOfPoints, curve )
{
var dt;
var i;
dt = 1.0 / ( numberOfPoints - 1 );
for( i = 0; i < numberOfPoints; i++)
curve[i] = PointOnCubicBezier( cp, i*dt );
}

//四个控制中点
var cp=[
//new Point2D(20, 0), new Point2D(100, 200), new Point2D(300, -200), new Point2D(400, 0)
new Point2D(500, 0), new Point2D(400,100), new Point2D(50, -350), new Point2D(0, -500)
];
//控制速度
var numberOfPoints=100;
var curve=[];
ComputeBezier( cp, numberOfPoints, curve );

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");

ctx.beginPath()
for(var i=0;i<curve.length;i++)
{
   console.log(curve[i].x)

   ctx.lineTo(curve[i].x,curve[i].y);
}
   ctx.strokeStyle="green";
       ctx.stroke();

/*var i=0, dot=document.getElementById("dotMove");
setInterval(function (){
var j = (i<100)?i:(199-i);
dot.style.left=curve[j].x+'px';
dot.style.top=100-curve[j].y+'px';
if(++i==200)i=0;
}, 50);*/
</script>

猜你喜欢