HTML5 Canvas阴影使用方法实例演示

前端技术 2023/09/04 HTML
HTML5 Canvas中提供了设置阴影的四个属性值分别为：
context.shadowColor = “red” 表示设置阴影颜色为红色
context.shadowOffsetX = 0表示阴影相对TEXT的水平距离，0表示两者水平位置重合
context.shadowOffsetY = 0表示阴影相对TEXT的垂直距离，0表示两者垂直位置重合
context.shadowBlur = 10 阴影模糊效果，值越大模糊越厉害。
一个最简单的带有阴影的矩形代码如下：
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.fillRect(10, hh+10, 200,canvas.height/4-20);
效果如下：
 
阴影文字：
只要设置shadowOffsetX与shadowOffsetY的值，当值都正数时，阴影相对文字的右下
方偏移。当值都为负数时，阴影相对文字的左上方偏移。
3D拉影效果：
在同一位置不断的重复绘制文字同时改变shadowOffsetX、shadowOffsetY、shadowBlur
的值，从小到大不断偏移不断增加，透明度也不断增加。就得到了拉影效果文字。
边缘模糊效果文字：
在3D拉影效果的基础上在四个方向重复，就得到了边缘羽化的文字效果。
运行效果：
 
序代码：

复制代码
代码如下:

<!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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