canvas仿写贝塞尔曲线的示例代码

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 canvas{ border: 1px solid black;}

 var canvas = document.getElementById("mycanvas"); var context = canvas.getContext("2d"); var x1 = 100; var y1 = 100; var x2 = 400; var y2 = 400; draw(); function draw(){ //画半透明的线 context.beginPath(); context.moveTo(500,0); context.lineTo(0,500); context.strokeStyle = "rgba(0,0,0,0.3)"; context.lineWidth = 10; context.stroke(); //画连接线 context.beginPath(); context.moveTo(0,500); context.lineTo(x1,y1); context.lineWidth = 2; context.strokeStyle = "black"; context.stroke(); context.beginPath(); context.moveTo(500,0); context.lineTo(x2,y2); context.lineWidth = 2; context.strokeStyle = "black"; context.stroke(); //画红球 context.beginPath(); context.arc(x1,y1,10,0,Math.PI*2); context.fillStyle = "orange"; context.fill(); //画蓝球 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 = 5; 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.offsetX; var y = ev.offsetY; //判断是否在红球上 var dis = Math.pow((x-x1),2) + Math.pow((y-y1),2); if(dis<100){ console.log("鼠标在红球上"); canvas.onmousemove = function(e){ var ev = e || window.event; var xx = ev.offsetX; var yy = ev.offsetY; //清除画布 context.clearRect(0,0,canvas.width,canvas.height); x1 = xx; y1 = yy; //重绘制 draw(); } } //判断鼠标是否在蓝球上 var dis = Math.pow((x-x2),2) + Math.pow((y-y2),2); if(dis<100){ canvas.onmousemove = function(e){ var ev = e || window.event; var xx1 = ev.offsetX; var yy1 = ev.offsetY; //清除画布 context.clearRect(0,0,canvas.width,canvas.height); x2 = xx1; y2 = yy1; //重绘制 draw(); } } } document.onmouseup =function(){ canvas.onmousemove = " "; }