两条平滑曲线相乘_[前端]使用曲线将多点连成一条平滑的曲线

之前在写一个项目需要把多点连成平滑的曲线，而且这些点是无法预知的。开始想到用贝塞尔曲线，但是具体贝塞尔曲线的控制点要怎么设定，怎样让多点都落在曲线上而且保持曲线的平滑，就一直没想到。

后来参考了一篇《Android 使用贝塞尔曲线将多点连成一条平滑的曲线》的博文，地址：http://m.blog.csdn.net/article/details?id=52667896

写得挺好的，不过没太仔细研究

原代码是java的，然后就直接用原代码改成了js版本的(虽然最后用了其他方式来实现……不过这个如果做什么在线生成图表什么的可以用上)

效果：

Paste_Image.png

后面的点契合的挺好的

代码：

var mPointList = [{x:10,y:10},{x:120,y:40},{x:260,y:180},{x:380,y:40},{x:420,y:120},

{x:510,y:110},{x:620,y:140},{x:760,y:280},{x:880,y:240},{x:920,y:120}];

var lineSmoothness = 0.16;

measurePath(mPointList,lineSmoothness);

function measurePath(mPointList,lineSmoothness) {

var prePreviousPointX ;

var prePreviousPointY ;

var previousPointX ;

var previousPointY ;

var currentPointX ;

var currentPointY ;

var nextPointX;

var nextPointY;

var lineSize = mPointList.length;

var c=document.getElementById("myCanvas");

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

ctx.strokeStyle="#FF0000";

ctx.beginPath();

for (var valueIndex = 0; valueIndex < lineSize; ++valueIndex) {

if (currentPointX) {

var point = mPointList[valueIndex];

currentPointX = point.x;

currentPointY = point.y;

}

if (previousPointX) {

//是否是第一个点

if (valueIndex > 0) {

var point = mPointList[valueIndex-1];

previousPointX = point.x;

previousPointY = point.y;

} else {

//是的话就用当前点表示上一个点

previousPointX = currentPointX;

previousPointY = currentPointY;

}

}

if (prePreviousPointX) {

//是否是前两个点

if (valueIndex > 1) {

var point = mPointList[valueIndex-2];

prePreviousPointX = point.x;

prePreviousPointY = point.y;

} else {

//是的话就用当前点表示上上个点

prePreviousPointX = previousPointX;

prePreviousPointY = previousPointY;

}

}

// 判断是不是最后一个点了

if (valueIndex < lineSize - 1) {

var point = mPointList[valueIndex+1];

nextPointX = point.x;

nextPointY = point.y;

} else {

//是的话就用当前点表示下一个点

nextPointX = currentPointX;

nextPointY = currentPointY;

}

if (valueIndex == 0) {

// 将Path移动到开始点

ctx.moveTo(mPointList[0].x,mPointList[0].y);

} else {

// 求出控制点坐标

var firstDiffX = (currentPointX - prePreviousPointX);

var firstDiffY = (currentPointY - prePreviousPointY);

var secondDiffX = (nextPointX - previousPointX);

var secondDiffY = (nextPointY - previousPointY);

var firstControlPointX = previousPointX + (lineSmoothness * firstDiffX);

var firstControlPointY = previousPointY + (lineSmoothness * firstDiffY);

var secondControlPointX = currentPointX - (lineSmoothness * secondDiffX);

var secondControlPointY = currentPointY - (lineSmoothness * secondDiffY);

//画出曲线

ctx.bezierCurveTo(firstControlPointX, firstControlPointY, secondControlPointX, secondControlPointY,

currentPointX, currentPointY);

}

// 更新值,

prePreviousPointX = previousPointX;

prePreviousPointY = previousPointY;

previousPointX = currentPointX;

previousPointY = currentPointY;

currentPointX = nextPointX;

currentPointY = nextPointY;

}

ctx.stroke();

}

//画点

var c=document.getElementById("myCanvas");

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

ctx.fillStyle="#000";

for (var i=0;i

ctx.beginPath();

ctx.arc(mPointList[i].x,mPointList[i].y,5,0,Math.PI*2,true);

ctx.closePath();

ctx.fill();

}