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實例講解使用HTML5 Canvas繪制陰影效果的方法

創(chuàng)建陰影效果需要操作以下4個屬性：

1.context.shadowColor：陰影顏色。
2.context.shadowOffsetX：陰影x軸位移。正值向右，負值向左。
3.context.shadowOffsetY：陰影y軸位移。正值向下，負值向上。
4.context.shadowBlur：陰影模糊濾鏡。數(shù)據(jù)越大，擴散程度越大。
這四個屬性只要設(shè)置了第一個和剩下三個中的任意一個就有陰影效果。不過通常情況下，四個屬性都要設(shè)置。

例如，創(chuàng)建一個向右下方位移各5px的紅色陰影，模糊2px，可以這樣寫。

JavaScript Code復(fù)制內(nèi)容到剪貼板

context.shadowColor = "red";
context.shadowOffsetX = 5;
context.shadowOffsetY = 5;
context.shadowBlur= 2;

需要注意的是，這里的陰影同其他屬性設(shè)置一樣，都是基于狀態(tài)的設(shè)置。因此，如果只想為某一個對象應(yīng)用陰影而不是全局陰影，需要在下次繪制前重置陰影的這四個屬性。
運行結(jié)果：

陰影文字：

只要設(shè)置shadowOffsetX與shadowOffsetY的值，當(dāng)值都正數(shù)時，陰影相對文字的右下

方偏移。當(dāng)值都為負數(shù)時，陰影相對文字的左上方偏移。

3D拉影效果：

在同一位置不斷的重復(fù)繪制文字同時改變shadowOffsetX、shadowOffsetY、shadowBlur

的值，從小到大不斷偏移不斷增加，透明度也不斷增加。就得到了拉影效果文字。

邊緣模糊效果文字：

在3D拉影效果的基礎(chǔ)上在四個方向重復(fù)，就得到了邊緣羽化的文字效果。

運行效果：

程序代碼：

JavaScript Code復(fù)制內(nèi)容到剪貼板

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="chrome=IE8">
<meta http-equiv="Content-type" content="text/html;charset=UTF-8">
<title>Canvas Clip Demo</title>
<link href="default.css" rel="stylesheet" />
<script>
var ctx = null; // global variable 2d context
var imageTexture = null;
window.onload = function() {
var canvas = document.getElementById("text_canvas");
console.log(canvas.parentNode.clientWidth);
canvas.width = canvas.parentNode.clientWidth;
canvas.height = canvas.parentNode.clientHeight;
if (!canvas.getContext) {
console.log("Canvas not supported. Please install a HTML5 compatible browser.");
return;
}
var context = canvas.getContext('2d');
// section one - shadow and blur
context.fillStyle="black";
context.fillRect(0, 0, canvas.width, canvas.height/4);
context.font = '60pt Calibri';
context.shadowColor = "white";
context.shadowOffsetX = 0;
context.shadowOffsetY = 0;
context.shadowBlur = 20;
context.fillText("Blur Canvas", 40, 80);
context.strokeStyle = "RGBA(0, 255, 0, 1)";
context.lineWidth = 2;
context.strokeText("Blur Canvas", 40, 80);
// section two - shadow font
var hh = canvas.height/4;
context.fillStyle="white";
context.fillRect(0, hh, canvas.width, canvas.height/4);
context.font = '60pt Calibri';
context.shadowColor = "RGBA(127,127,127,1)";
context.shadowOffsetX = 3;
context.shadowOffsetY = 3;
context.shadowBlur = 0;
context.fillStyle = "RGBA(0, 0, 0, 0.8)";
context.fillText("Blur Canvas", 40, 80+hh);
// section three - down shadow effect
var hh = canvas.height/4 + hh;
context.fillStyle="black";
context.fillRect(0, hh, canvas.width, canvas.height/4);
for(var i = 0; i < 10; i++)
{
context.shadowColor = "RGBA(255, 255, 255," + ((10-i)/10) + ")";
context.shadowOffsetX = i*2;
context.shadowOffsetY = i*2;
context.shadowBlur = i*2;
context.fillStyle = "RGBA(127, 127, 127, 1)";
context.fillText("Blur Canvas", 40, 80+hh);
}
// section four - fade effect
var hh = canvas.height/4 + hh;
context.fillStyle="green";
context.fillRect(0, hh, canvas.width, canvas.height/4);
for(var i = 0; i < 10; i++)
{
context.shadowColor = "RGBA(255, 255, 255," + ((10-i)/10) + ")";
context.shadowOffsetX = 0;
context.shadowOffsetY = -i*2;
context.shadowBlur = i*2;
context.fillStyle = "RGBA(127, 127, 127, 1)";
context.fillText("Blur Canvas", 40, 80+hh);
}
for(var i = 0; i < 10; i++)
{
context.shadowColor = "RGBA(255, 255, 255," + ((10-i)/10) + ")";
context.shadowOffsetX = 0;
context.shadowOffsetY = i*2;
context.shadowBlur = i*2;
context.fillStyle = "RGBA(127, 127, 127, 1)";
context.fillText("Blur Canvas", 40, 80+hh);
}
for(var i = 0; i < 10; i++)
{
context.shadowColor = "RGBA(255, 255, 255," + ((10-i)/10) + ")";
context.shadowOffsetX = i*2;
context.shadowOffsetY = 0;
context.shadowBlur = i*2;
context.fillStyle = "RGBA(127, 127, 127, 1)";
context.fillText("Blur Canvas", 40, 80+hh);
}
for(var i = 0; i < 10; i++)
{
context.shadowColor = "RGBA(255, 255, 255," + ((10-i)/10) + ")";
context.shadowOffsetX = -i*2;
context.shadowOffsetY = 0;
context.shadowBlur = i*2;
context.fillStyle = "RGBA(127, 127, 127, 1)";
context.fillText("Blur Canvas", 40, 80+hh);
}
}
</script>
</head>
<body>
<h1>HTML5 Canvas Clip Demo - By Gloomy Fish</h1>
<pre>Fill And Stroke Clip</pre>
<div id="my_painter">
<canvas id="text_canvas"></canvas>
</div>
</body>
</html>

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