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HTML5 Canvas shadow usage demonstration and code details

黄舟
黄舟Original
2017-03-03 16:02:201834browse

HTML5 Canvas shadow usage demonstration

HTML5 Canvas provides four attribute values ​​​​for setting shadows:

context.shadowColor = "red" means setting the shadow color to red

context.shadowOffsetX = 0 means the horizontal distance of the shadow relative to TEXT, 0 means the horizontal position of the two Coincidence

context.shadowOffsetY = 0 indicates the vertical distance of the shadow relative to TEXT, 0 indicates that the vertical positions of the two coincide with each other

context.shadowBlur = 10 Shadow blur effect, the larger the value, the more severe the blur.

The simplest code for a rectangle with a shadow is as follows: 

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);


##The effect is as follows:


#Shadow text:


As long as the values ​​​​of shadowOffsetX and shadowOffsetY are set, when the values ​​​​are both positive numbers, the shadow will be offset from the lower right

of the text shift. When the values ​​are all negative, the shadow is offset relative to the upper left of the text.

3D shadow effect:

Continuously and repeatedly draw text at the same position while changing shadowOffsetX, shadowOffsetY, shadowBlur The value of

is continuously offset from small to large, and the transparency is also increasing. You get the shadow effect text.

Edge blur effect text:

Repeat in four directions based on the 3D shadow effect. The text effect of edge feathering is obtained.

Running effect:


##Program code: 

<!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(&#39;2d&#39;);
			
			// section one - shadow and blur
			context.fillStyle="black";
			context.fillRect(0, 0, canvas.width, canvas.height/4);
			context.font = &#39;60pt Calibri&#39;;
			
			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 = &#39;60pt Calibri&#39;;
			
			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 class="brush:php;toolbar:false">Fill And Stroke Clip

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