canvas实现拉伸贝塞尔曲线(简约版)鼠标点击移动红色,深青色实现曲线的变动@慕课网原创_慕课网

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>自制贝塞尔曲线拉伸</title>
        <style type="text/css">
            *{
                padding: 0;
                margin: 0;
            }
            #canvas{
                border: 1px solid saddlebrown;
                box-shadow: 2px 3px 4px 4px gray;
            }
        </style>
    </head>
    <body>
        <canvas id="canvas" width="600" height="700">
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        </canvas>
        <canvas id="canvasWater"  width="300" height="200"></canvas>
    </body>
    <script type="text/javascript">
        var canvas = document.getElementById('canvas');
        var context = canvas.getContext('2d');
        var canvasWater = document.getElementById('canvasWater');
        var contextWater = canvasWater.getContext('2d');
        var x1Sb = 0;//用于鼠标移动时的x值
        var y1Sb = 0;//用于鼠标移动时的y值
        var x2Sb = 0;//用于鼠标移动时的x值
        var y2Sb = 0;//用于鼠标移动时的y值
//      红色小球
        var redBall = {
            x:100,
            y:200,
            r:15,
            draw:function(){
                context.beginPath();
                context.arc(this.x,this.y,this.r,0,Math.PI*2,false);
                context.fillStyle ='red';
                context.fill();
            }
        }
//      青色小球
        var cyanBall = {
            x:500,
            y:600,
            r:15,
            draw:function(){
                context.beginPath();
                context.arc(this.x,this.y,this.r,0,Math.PI*2,false);
                context.fillStyle ='darkcyan';
                context.fill();
            }
        }
        function noChange (){
            context.beginPath();
            context.moveTo(100,600);
            context.lineTo(100,200);
            context.closePath();
            context.lineWidth = 1;
            context.strokeStyle = 'black';
            context.stroke();
    //      -------------------
            context.beginPath();
            context.moveTo(100,600);
            context.lineTo(500,600);
            context.closePath();
            context.lineWidth = 1;
            context.strokeStyle = 'black';
            context.stroke();
    //      ----------------------
            context.beginPath();
            context.arc(100,600,15,0,2*Math.PI,false);
            context.closePath();
            context.fillStyle = 'white';
            context.fill();
            context.lineWidth = 1;
            context.strokeStyle = 'gray';
            context.stroke();
    //      ------------
            context.beginPath();
            context.arc(500,200,15,0,2*Math.PI,false);
            context.closePath();
            context.fillStyle = 'white';
            context.fill();
            context.lineWidth = 1;
            context.strokeStyle = 'gray';
            context.stroke();
        }
        function longLine (){
//      ----------------------
            context.beginPath();
            context.moveTo(100,600);
            context.lineTo(500,200);
            context.closePath();
            context.lineWidth = 5;
            context.lineCap = 'round';
            context.strokeStyle = 'lightgray';
            context.stroke();
        }
//      ------------------
        noChange();
        redBall.draw();
        cyanBall.draw();
//      建立画红线的函数
        function drawRed (xR,yR){
            context.beginPath();
            context.moveTo(100,600);
            context.lineTo(xR,yR);
            context.closePath();
            context.strokeStyle = 'lightgray';
            context.stroke();
        }
//      建立画青线的函数
        function drawCyan (xC,yC){
            context.beginPath();
            context.moveTo(500,200);
            context.lineTo(xC,yC);
            context.closePath();
            context.strokeStyle = 'lightgray';
            context.stroke();
        }
//      建立画贝塞尔曲线的函数
        function drawbsr (x1,y1,x2,y2){
            context.beginPath();
            context.moveTo(100,600);
            context.bezierCurveTo(x1,y1,x2,y2,500,200);
//          context.closePath();
            context.lineWidth = 8;
            context.strokeStyle = 'black';
            context.stroke();
            console.log(4);
        }

        noChange();
        var xB1S = 100;
        var yB1S = 200;
        var xB2S = 500;
        var yB2S = 600;
        canvas.onmousedown = function(e){
            var event = window.event  e;
            var xd = event.clientX;
            var yd = event.clientY;
//          如果点击的是红色圆
            if(xd>=redBall.x-redBall.r&&xd<=redBall.x+redBall.r&&yd>=redBall.y-redBall.r&&yd<=redBall.y+redBall.r){
                canvas.onmousemove = function(e){
                    context.clearRect(0,0,canvas.width,canvas.height);
                    var event = window.event  e;
                    x1Sb = event.clientX;
                    y1Sb = event.clientY;
                    redBall.x = x1Sb;
                    redBall.y = y1Sb;
                    xB1S = x1Sb;
                    yB1S = y1Sb;
                    drawRed(x1Sb,y1Sb);

                    drawCyan(xB2S,yB2S);

                    longLine();
                    drawbsr(x1Sb,y1Sb,xB2S,yB2S);
                    noChange();
                    redBall.draw();
                    cyanBall.draw();
                    context.drawImage(canvasWater,0,0,300,200,200,550,300,200);
//                  console.log(x1Sb,y1Sb,xB2S,yB2S);
//                  console.log(1);
                }
            }
//          如果点击的是青色圆
        if(xd>=cyanBall.x-cyanBall.r&&xd<=cyanBall.x+cyanBall.r&&yd>=cyanBall.y-cyanBall.r&&yd<=cyanBall.y+cyanBall.r){
            canvas.onmousemove = function(e){
                context.clearRect(0,0,canvas.width,canvas.height);
                var event = window.event  e;
                x2Sb = event.clientX;
                y2Sb = event.clientY;
                cyanBall.x = x2Sb;
                cyanBall.y =y2Sb;
                xB2S = x2Sb;
                yB2S = y2Sb;
                drawRed(xB1S,yB1S);
                drawCyan(x2Sb,y2Sb);
                longLine();
                drawbsr(xB1S,yB1S,x2Sb,y2Sb);
                noChange();
                redBall.draw();
                cyanBall.draw();
//              console.log(x2Sb,y2Sb,xB1S,yB1S);
                context.drawImage(canvasWater,0,0,300,200,200,550,300,200);
                }
            }
        }
//      鼠标松开事件
        canvas.onmouseup = function(e){
                    canvas.onmousemove = null;
            }   
//添加水印
        contextWater.beginPath();
//      创建线性渐变
        var linear = contextWater.createLinearGradient(100,100,300,100);
//      设置过程和颜色
        linear.addColorStop(0,'blue');
        linear.addColorStop(0.5,'purple');
        linear.addColorStop(1,'cyan');
        contextWater.font = 'italic 30px 行楷';

        contextWater.strokeStyle = linear;
        contextWater.strokeText('-o-小涛涛作品-.-',100,100);
        context.drawImage(canvasWater,0,0,300,200,200,550,300,200);
    </script>
</html>