HTML5 Canvas阴影用法演示
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：
程序代码：
<!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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