首页 > 代码库 > HTML5 Canvas ( 线性渐变, 升级版的星空 ) createLinearGradient, addColorStop

HTML5 Canvas ( 线性渐变, 升级版的星空 ) createLinearGradient, addColorStop

2024-09-10 21:08:46   220人阅读

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <script type="text/javascript" src="../js/jQuery.js"></script>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
            outline: none;
            border: none;
        }
        #canvas{
            width: 7rem;
            margin: .25rem 0 0 1.5rem;
            border: 1px solid black;
        }
    </style>
</head>
<body> 
    <canvas id="canvas" width="1000" height="600"></canvas>
</body>
</html>
<script type="text/javascript">
    /**
     * rem 布局初始化
     */
    $(‘html‘).css(‘font-size‘, $(window).width()/10);
    /**
     * 获取 canvas 画布
     * 获取 canvas 绘图上下文环境
     */
    var canvas = $(‘#canvas‘)[0];
    var cxt = canvas.getContext(‘2d‘);
    
    /**
     * 线性渐变 createLinearGradient
     * 添加颜色 addColorStop( 该颜色起始位置的百分比, 颜色 )
     */
    var lineStyle = cxt.createLinearGradient(0, 0, 1000, 600); //确定线性渐变的位置
    lineStyle.addColorStop(0.0, ‘red‘); //渐变样式的添加 
    lineStyle.addColorStop(0.5, ‘yellow‘); //渐变样式的添加
    lineStyle.addColorStop(1.0, ‘blue‘); //渐变样式的添加 
    cxt.fillStyle = lineStyle;
    cxt.fillRect(0, 0, 1000, 600);
</script>
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <script type="text/javascript" src="../js/jQuery.js"></script>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
            outline: none;
            border: none;
        }
        #canvas{
            width: 7rem;
            margin: .25rem 0 0 1.5rem;
            border: 1px solid black;
        }
    </style>
</head>
<body> 
    <canvas id="canvas" width="1000" height="600"></canvas>
</body>
</html>
<script type="text/javascript">
    /**
     * rem 布局初始化
     */
    $(‘html‘).css(‘font-size‘, $(window).width()/10);
    /**
     * 获取 canvas 画布
     * 获取 canvas 绘图上下文环境
     */
    var canvas = $(‘#canvas‘)[0];
    var cxt = canvas.getContext(‘2d‘);
    
    /**
     * 绘制一片星空
     */
    var skyStyle = cxt.createLinearGradient(0, 0, 0, canvas.height);
    skyStyle.addColorStop(0.0, ‘black‘);
    skyStyle.addColorStop(1.0, ‘#035‘);
    cxt.fillStyle = skyStyle;
    
    cxt.fillRect(0, 0, canvas.width, canvas.height);
    for(var i = 0; i < 150; i++){
        var fiveStart = {};
        fiveStart.Radius = Math.random()*6+6;
        fiveStart.offsetX = Math.random()*canvas.width;
        fiveStart.offsetY = Math.random()*canvas.height*0.65;
        fiveStart.RotationAngle = Math.random()*360;
        
        drawFiveStar(cxt, fiveStart);
    }
    
    /**
     * 控制五角星的方法
     */
    function drawFiveStar(cxt, fiveStart){
        cxt.save();
        cxt.translate(fiveStart.offsetX, fiveStart.offsetY); //相对于原点的偏移量
        cxt.rotate(fiveStart.RotationAngle/180*Math.PI); //图形旋转(弧度)
        cxt.scale(fiveStart.Radius, fiveStart.Radius); //图形缩放( X轴的倍数, Y轴的倍数 )
        fiveStartPath(cxt);
        cxt.fillStyle = "yellow";
        cxt.fill();
        cxt.restore();
    }
    
    /**
     * 绘制标准五角星路径的方法
     */
    function fiveStartPath(cxt){
        cxt.beginPath();
        var x = 0; y = 0;
        for(var i = 0; i < 5; i++){
            x = Math.cos((18+72*i)/180*Math.PI);
            y = Math.sin((18+72*i)/180*Math.PI);
            cxt.lineTo(x, 0-y);
            x = Math.cos((54+72*i)/180*Math.PI)/2.0;
            y = Math.sin((54+72*i)/180*Math.PI)/2.0;
            cxt.lineTo(x, 0-y);
        }
        cxt.closePath();
    }
</script>

 

HTML5 Canvas ( 线性渐变, 升级版的星空 ) createLinearGradient, addColorStop


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