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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/u4moxsmpxti227545.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/j4ahvayv50e227546.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/gh40btwftoq227547.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/cl00dvvrmdy227548.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/fpkrggvlyo0227549.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/absdyilf4ly227550.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/gw2flgtgq4q227551.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/fea4vwgecjn227552.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/0q5mmz4s2g4227553.png)
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>
![[js高手之路] html5 canvas系列教程 – 线形渐变,径向渐变与阴影设置](https://img.zhankr.net/n3z1rahps20227554.png)
