HTML5 Game - Drawing Quadratic Bezier Curves

Introduction

A quadratic Bezier curve has only one control point.
Demo

<!DOCTYPE HTML>
<html>
    <head>
        <title>Example</title>
        <style>
            canvas {border: thin solid black}
            body > * {float:left;}
        </style>
    </head>
    <body>
        <canvas id="canvas" width="500" height="140">
            Your browser doesn't support the <code>canvas</code> element
        </canvas>
        <script>
            let canvasElem = document.getElementById("canvas");
            let ctx = canvasElem.getContext("2d");

            let startPoint = [50, 100];//from  www. j  a  v  a  2s.  com
            let endPoint = [400, 100];
            let cp1 = [250, 50];
            
            canvasElem.onmousemove = function(e) {
                if (e.shiftKey) {
                    cp1 = [e.clientX, e.clientY];
                }
                ctx.clearRect(0, 0, 500, 140);
                draw();
            }
            
            draw();

            function draw() {
                ctx.lineWidth = 3;
                ctx.strokeStyle = "black";                  
                ctx.beginPath();
                ctx.moveTo(startPoint[0], startPoint[1]);
                ctx.quadraticCurveTo(cp1[0], cp1[1], endPoint[0], endPoint[1]);
                ctx.stroke();
    
                ctx.lineWidth = 1;
                ctx.strokeStyle = "red";            
                let points = [startPoint, endPoint, cp1];
                for (let i = 0; i < points.length; i++) {
                    drawPoint(points[i]);    
                }
                drawLine(startPoint, cp1);
                drawLine(endPoint, cp1);
            }

            function drawPoint(point) {
                ctx.beginPath();

                ctx.strokeRect(point[0] -2, point[1] -2, 4, 4);
            }
            
            function drawLine(from, to) {
                ctx.beginPath();
                ctx.moveTo(from[0], from[1]);
                ctx.lineTo(to[0], to[1]);
                ctx.stroke();
            }
        </script>
    </body>
</html>
HTML5 Game - Drawing Quadratic Bezier Curves

Introduction

Demo

Related Topic
