贝塞尔曲线
bezierCurveTo(cpx,cpy,cpx2,cpx2,dx,dy);创建一条表示贝塞尔曲线的路径.
该函数接受六个参数,分别代表三个点.
(cpx,cpy),(cpx2,cpx2)代表控制点,决定曲线的形状
(dx,dy)代表终点
模拟贝塞尔曲线（isPointInPath）
isPointInPath方法
isPointInPath
是 Canvas 2D API 用于检测某点是否在路径的描边线上的方法。返回值是一个布尔值，当这个点在路径的描边线上，则返回true，否则返回false。
首先强调isPointInPath(x,y)方法是针对路径的，比如canvas中的rect、arc方法都可以用，但是fillRect不可以用，因为它不是路径；而且仅对当前的路径有效，而且如果当前路径有多个子路径（currentPath可以有多个subPath：比如进行了rect()之后，再进行arc()，最后关闭路径，进行stroke，那么rect()和arc()所绘制的就是当前路径的两个子路径），只对第一个子路径有效
所以要在每次判断之前要创建要移动的元素
<script type="text/javascript">
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var redX1 = 100;
var redY1 = 200;
var blueX1 = 400;
var blueY1 = 200;
function createLine(moveTo1,moveTo2,lineTo1,lineTo2,lineWidth,color){
context.beginPath();
context.moveTo(moveTo1,moveTo2);
context.lineTo(lineTo1,lineTo2);
context.lineWidth = lineWidth;
context.strokeStyle = color;
context.stroke();
}
drawLine(redX1,redY1,blueX1,blueY1);
function drawLine(redX1,redY1,blueX1,blueY1){
//半透明的粗线
createLine(0,500,500,0,10,"rgba(0,0,0,0.2)");
//连接到红色小球的黑线
createLine(0,500,redX1,redY1,5,"black");
//连接到蓝球的黑线
createLine(500,0,blueX1,blueY1,5,"black");
//绘制贝塞尔曲线
context.beginPath();
context.moveTo(0,500);
context.bezierCurveTo(redX1,redY1,blueX1,blueY1,500,0);
context.stroke();
function createBall(color,x,y){
console.log(x,y)
context.beginPath();
context.fillStyle = color;
context.arc(x,y,10,0,Math.PI*2);
context.fill();
}
function createBallB(color,x,y){
console.log(x,y)
context.beginPath();
context.fillStyle = color;
context.arc(x,y,10,0,Math.PI*2);
context.fill();
}
//蓝球
createBallB("blue",blueX1,blueY1);
//红球
createBall("red",redX1,redY1);
canvas.onmousedown = function(e){
var ev = window.event || e;
var x = ev.clientX - canvas.offsetLeft;
var y = ev.clientY - canvas.offsetTop;
createBallB("blue",blueX1,blueY1);
if(context.isPointInPath(x,y)){
canvas.onmousemove = function(e){
var ev = window.event || e;
var xx = ev.clientX - canvas.offsetLeft;
var yy = ev.clientY - canvas.offsetTop;
blueX1 = xx;
blueY1 = yy;
context.clearRect(0,0,canvas.offsetWidth,canvas.offsetHeight);
drawLine(redX1,redY1,blueX1,blueY1);
}
}
createBall("red",redX1,redY1);
if(context.isPointInPath(x,y)){
canvas.onmousemove = function(e){
var ev = window.event || e;
var xx = ev.clientX - canvas.offsetLeft;
var yy = ev.clientY - canvas.offsetTop;
redX1 = xx;
redY1 = yy;
context.clearRect(0,0,canvas.offsetWidth,canvas.offsetHeight);
drawLine(redX1,redY1,blueX1,blueY1);
}
}
}
}
document.onmouseup = function(){
canvas.onmousemove = "";
}
</script>
原生方法
利用点击该点的位置到圆心的距离与半径相比，如果大于半径，则表明点击的位置不在小球内部，反之，则在小球内部
<script type="text/javascript">
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var x1 = 100;
var y1 = 100;
var x2 = 400;
var y2 = 400;
draw(x1,y1,x2,y2);
function draw(x1,y1,x2,y2){
//画半透明的线
context.beginPath();
context.moveTo(500,0);
context.lineTo(0,500);
context.lineWidth = 10;
context.strokeStyle = "rgba(0,0,0,0.2)";
context.stroke();
//画连接线
context.beginPath();
context.moveTo(0,500);
context.lineTo(x1,y1);
context.lineWidth = 4;
context.strokeStyle = "#000000";
context.stroke()
//画连接线
context.beginPath();
context.moveTo(500,0);
context.lineTo(x2,y2);
context.lineWidth = 4;
context.strokeStyle = "#000000";
context.stroke()
//花红球
context.beginPath();
context.arc(x1,y1,10,0,Math.PI*2);
context.fillStyle = "#FF0000";
context.fill();
//花蓝球
context.beginPath();
context.arc(x2,y2,10,0,Math.PI*2);
context.fillStyle = "blue";
context.fill();
//画贝塞尔曲线
context.beginPath();
context.moveTo(0,500);
context.bezierCurveTo(x1,y1,x2,y2,500,0);
context.lineWidth = 10;
context.stroke();
//拖动小球 做动画
//判断是否拖动小球
//如果在小球上就做动画
canvas.onmousedown = function(e){
var ev = e || window.event;
var x= ev.clientX - canvas.offsetLeft;
var y = ev.clientY - canvas.offsetTop;
//判断是否在红球上
var disRed = Math.pow((x - x1),2) + Math.pow((y - y1),2);
if(disRed < 100){
console.log("鼠标在红球上");
canvas.onmousemove = function(e){
var ev = window.event || e;
var xx = ev.clientX - canvas.offsetLeft;
var yy = ev.clientY - canvas.offsetTop;
//清除画布
context.clearRect(0,0,canvas.width,canvas.height);
//重绘
x1 = xx;
y1 = yy;
draw(x1,y1,x2,y2);
}
}
//判断是否在蓝球上
var disBlue = Math.pow((x - x2),2) + Math.pow((y - y2),2);
if(disBlue < 100){
console.log("鼠标在红球上");
canvas.onmousemove = function(e){
var ev = window.event || e;
var xx = ev.clientX - canvas.offsetLeft;
var yy = ev.clientY - canvas.offsetTop;
//清除画布
context.clearRect(0,0,canvas.width,canvas.height);
//重绘
x2 = xx;
y2 = yy;
draw(x1,y1,x2,y2);
}
}
}
}
document.onmouseup = function(){
canvas.onmousemove = "";
}
</script>
