canvas-8searchLight4.html

时间：2022-03-13 18:40:21
<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>Document</title>

</head>

<body>

    <canvas id="canvas" style="margin:0 auto;border:1px #ddd solid">

        The current browser does not support Canvas, can replace the browser a try!

    </canvas>

    <script>

        var searchLight = {

            x : 400,

            y : 400,

            radius : 150,

            vx : Math.random() * 5 + 10,

            vy : Math.random() * 5 + 10

        }

        var isIncrease = true;

        window.onload = function(){

            var canvas = document.getElementById('canvas');

            canvas.width = 1024;

            canvas.height = 768;

            if(canvas.getContext('2d')){

                var context = canvas.getContext('2d');

                setInterval(function(){

                        draw(context);

                        update(canvas.width,canvas.height);

                },40);

            }else{

                alert('当前游览器不支持Canvas，请更换游览器后再试！');

            }

        }

        function draw(cxt){

            var canvas = cxt.canvas;

            cxt.clearRect(0,0,canvas.width,canvas.height);

            cxt.save();

                cxt.beginPath();

                    cxt.fillStyle = "#000";

                    cxt.fillRect(0,0,canvas.width,canvas.height)

                cxt.closePath();

                cxt.save();

                    cxt.translate(searchLight.x,searchLight.y);

                    cxt.scale(searchLight.radius,searchLight.radius);

                    starPath(cxt);

                    cxt.fillStyle = "#fff";

                    cxt.fill();

                cxt.restore();

                    cxt.clip();

                cxt.font = "bold 150px Arial";

                cxt.textAlign = "center";

                cxt.textBaseline = "middle";

                cxt.fillStyle = "#058";

                cxt.fillText("Canvas",canvas.width/2,canvas.height/4);

                cxt.fillText("Canvas",canvas.width/2,canvas.height/2);

                cxt.fillText("Canvas",canvas.width/2,canvas.height * 3/4);

            cxt.restore();

        }

        function starPath(cxt){

            cxt.beginPath();

            for(var i=0;i<5;i++){

                cxt.lineTo(Math.cos( (18+i*72) / 180 * Math.PI ),

                                -Math.sin( (18+i*72) / 180 * Math.PI ));

                cxt.lineTo(Math.cos( (54+i*72) / 180 * Math.PI )*0.5,

                                -Math.sin( (54+i*72) / 180 * Math.PI )*0.5);

            }

            cxt.closePath();

        }

        function update(canvasWidth,canvasHeight){

            // rot += 1;

            // searchLight.x += searchLight.vx;

            // searchLight.y += searchLight.vy;

            // if(searchLight.x - searchLight.radius <= 0){

            //     searchLight.vx = -searchLight.vx;

            //     searchLight.x = searchLight.radius;

            // }

            // if(searchLight.x + searchLight.radius >= canvasWidth){

            //     searchLight.vx = -searchLight.vx;

            //     searchLight.x = canvasWidth - searchLight.radius;

            // }

            // if(searchLight.y - searchLight.radius <= 0){

            //     searchLight.vy = -searchLight.vy;

            //     searchLight.y = searchLight.radius;

            // }

            // if(searchLight.y + searchLight.radius >= canvasHeight){

            //     searchLight.vy = -searchLight.vy;

            //     searchLight.y = canvasHeight - searchLight.radius;

            // }

            if(searchLight.radius > 700)

                isIncrease = false;

            else if(searchLight.radius < 150)

                isIncrease = true;

            if(isIncrease)

                searchLight.radius += 5;

            else

                searchLight.radius -= 5;

        }

    </script>

</body>

</html>

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