[js高手之路] html5 canvas系列教程 - 线形渐变,径向渐变与阴影设置

接着上文[js高手之路] html5 canvas系列教程 - 像素操作(反色,黑白,亮度,复古,蒙版,透明)继续.

一、线形渐变

线形渐变指的是一条直线上发生的渐变。

用法：

var linear = cxt.createLinearGradient( x1, y1, x2, y2 );

linear.addColorStop( value1, color1 );

linear.addColorStop( value2, color2 );

.....

oGc.fillStyle = linear

oGc.fill();

1) createLinearGradient创建一个线形渐变对象. x1, y1表示渐变的起点. x2, y2表示渐变的终点.

2)addColorStop在某处添加渐变颜色值

3)fillStyle：把渐变对象作为填充样式

4)调用fill及其他相关图形进行渐变填充

水平渐变

 <head>

 <meta charset='utf-8' />

 <style>

 #canvas{

     border:1px dashed #aaa;

 }

 </style>

 <script>

 window.onload = function(){

     var oCanvas = document.querySelector( "#canvas" ),

         oGc = oCanvas.getContext( '2d' );

     var linear = oGc.createLinearGradient( 0, 400, 500, 400 );

     linear.addColorStop( 0, 'red' );

     linear.addColorStop( 1, '#09f' );

     oGc.fillStyle = linear;

     oGc.fillRect( 0, 0, 500, 400 );

 }

 </script>

 </head>

 <body>

 <canvas id="canvas" width="500" height="400"></canvas>

 </body>

垂直渐变：

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' );

         var linear = oGc.createLinearGradient( 400, 0, 400, 500 );

         linear.addColorStop( 0, 'red' );

         linear.addColorStop( 1, '#09f' );

         oGc.fillStyle = linear;

         oGc.fillRect( 0, 0, 500, 400 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

对角线渐变：

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' );

         var linear = oGc.createLinearGradient( 0, 0, 400, 500 );

         linear.addColorStop( 0, 'red' );

         linear.addColorStop( 1, '#09f' );

         oGc.fillStyle = linear;

         oGc.fillRect( 0, 0, 500, 400 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

为文字添加线形渐变效果

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             text = '跟着ghostwu学习html5 canvas教程';

             oGc.font = '22px bold 微软雅黑';

         var linear = oGc.createLinearGradient( 20, 100, 400, 100 );

         linear.addColorStop( 0, 'red' );

         linear.addColorStop( 1, '#09f' );

         oGc.fillStyle = linear;

         oGc.fillText( text, 50, 100 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

二、径向渐变

颜色渐变从一个起点向各个方向渐变，用法跟线形渐变差不多，只不过创建渐变的时候用的是另一个函数

var radial = cxt.createRadialGradient( x1, y1, r1, x2, y2, r2 )

....下面的步骤跟线形渐变一样，不再重复了

x1, y1起始点的圆心坐标，r1: 起始点圆的半径

x2，y2结束点的圆心坐标，r2:结束点圆所在的半径

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

         oGc.beginPath();

         oGc.arc( 100, 100, 100, 0, 360 * Math.PI / 180, false );

         oGc.closePath();

         var radial = oGc.createRadialGradient( 150, 50, 10, 100, 100, 100 );

         radial.addColorStop( 0.1, 'white' );

         radial.addColorStop( 0.6, 'orange' );

         radial.addColorStop( 1, 'red' );

         oGc.fillStyle = radial;

         oGc.fill();

         oGc.beginPath();

         oGc.arc( 320, 100, 100, 0, 360 * Math.PI / 180, false );

         oGc.closePath();

         var radial2 = oGc.createRadialGradient( 280, 50, 10, 320, 100, 100 );

         radial2.addColorStop( 0.1, 'white' );

         radial2.addColorStop( 0.6, 'orange' );

         radial2.addColorStop( 1, 'rgba( 255, 0, 0, 0.5 )' );

         oGc.fillStyle = radial2;

         oGc.fill();

         oGc.beginPath();

         oGc.lineWidth = 1;

         oGc.strokeStyle = '#eee';

         for( var i = 0; i < width; i += 10 ){

             oGc.moveTo( i, 0 );

             oGc.lineTo( i, height );

         }

         for( var j = 0; j < height; j += 10 ){

             oGc.moveTo( 0, j );

             oGc.lineTo( width, j );

         }

         oGc.closePath();

         oGc.stroke();

         oGc.beginPath();

         oGc.fillStyle = 'red';

         oGc.strokeStyle = 'blue';

         oGc.moveTo( 150, 0 );

         oGc.lineTo( 150, height );

         oGc.moveTo( 0, 50 );

         oGc.lineTo( width, 50 );

         oGc.fillText( '(150,50)', 170, 30 );

         oGc.stroke();

         oGc.closePath();

         oGc.beginPath();

         oGc.strokeStyle = 'yellow';

         oGc.fillStyle = 'black';

         oGc.moveTo( 100, 0 );

         oGc.lineTo( 100, height );

         oGc.moveTo( 0, 100 );

         oGc.lineTo( width, 100 );

         oGc.fillText( '(100,100)', 30, 120 );

         oGc.stroke();

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

我在图中做出了第一个径向渐变的圆心坐标，便于观看

同心圆渐变:

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

         var radial = oGc.createRadialGradient( 100, 100, 0, 100, 100, 100 );

         radial.addColorStop( 0, 'red' );

         radial.addColorStop( 0.25, 'orange' );

         radial.addColorStop( 0.5, 'yellow' );

         radial.addColorStop( 0.75, 'green' );

         radial.addColorStop( 1, '#09f' );

         oGc.fillStyle = radial;

         oGc.fillRect( 10, 10, 200, 200 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

三、阴影设置

跟css3的边框阴影用法差不多.

cxt.shadowOffsetX: 水平阴影，可以设置正负数, 正数->向右偏移，负数->向左偏移

cxt.shadowOffsetY: 垂直阴影，可以设置正负数，正数->向下偏移，负数->向上偏移

cxt.shadowColor: 阴影的颜色

cxt.shadowBlur: 阴影的模糊范围

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

             oGc.shadowOffsetX = 5;

             oGc.shadowOffsetY = 5;

             oGc.shadowColor = '#09f';

             oGc.shadowBlur = 10;

             oGc.fillStyle = 'red';

             oGc.fillRect( 10, 10, 100, 100 );

             oGc.shadowOffsetX = -5;

             oGc.shadowOffsetY = -5;

             oGc.shadowColor = '#09f';

             oGc.shadowBlur = 10;

             oGc.fillStyle = 'red';

             oGc.fillRect( 140, 20, 100, 100 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

给文字设置阴影：

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

             oGc.shadowOffsetX = 2;

             oGc.shadowOffsetY = 2;

             oGc.shadowColor = '#09f';

             oGc.shadowBlur = 1;

             oGc.font = '30px bold 微软雅黑';

             oGc.fillText( '跟着ghostwu学习html5 canvas', 20, 100 );

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

给图片设置阴影

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

             var oImg = new Image();

             oImg.src = './img/mv.jpg';

             oImg.onload = function(){

                 oGc.shadowOffsetX = 5;

                 oGc.shadowOffsetY = 5;

                 // oGc.shadowOffsetX = 0;

                 // oGc.shadowOffsetY = 0;

                 oGc.shadowColor = '#888';

                 oGc.shadowBlur = 20;

                 oGc.fillRect( 50, 20, 200, 200 );

                 oGc.drawImage( oImg, 50, 20 );

             }

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

给图片的四周设置阴影：

把shadowOffsetX和shadowOffsetY都设置为0，那么就会在四周产生阴影效果

 <head>

     <meta charset='utf-8' />

     <style>

     #canvas{

         border:1px dashed #aaa;

     }

     </style>

     <script>

     window.onload = function(){

         var oCanvas = document.querySelector( "#canvas" ),

             oGc = oCanvas.getContext( '2d' ),

             width = oCanvas.width, height = oCanvas.height;

             var oImg = new Image();

             oImg.src = './img/mv.jpg';

             oImg.onload = function(){

                 oGc.shadowOffsetX = 0;

                 oGc.shadowOffsetY = 0;

                 oGc.shadowColor = '#888';

                 oGc.shadowBlur = 20;

                 oGc.fillRect( 50, 20, 200, 200 );

                 oGc.drawImage( oImg, 50, 20 );

             }

     }

     </script>

 </head>

 <body>

     <canvas id="canvas" width="500" height="400"></canvas>

 </body>

巴特西

[js高手之路] html5 canvas系列教程 - 线形渐变,径向渐变与阴影设置

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