模拟贝塞尔曲线（isPointInPath）

2017-12-26

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>