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Usage examples of drawImage (image scaling or cropping) in H5 Canvas API
Usage examples of drawImage (image scaling or cropping) in H5 Canvas API
This article mainly introduces the usage examples of the drawImage() method in the HTML5 Canvas API. The drawImage() method is mainly used to scale or crop images. The article gives the usage of its coordinates and related parameters. Friends who need it You can refer to the following
drawImage() is a very key method. It can introduce images, canvases, and videos, and scale or crop them.
There are three forms of expression:
Syntax 1
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context.drawImage(img,dx,dy);
Grammar 2
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- ##context.drawImage(img,dx,dy,dw,dw); ##Syntax 3
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##context.drawImage(img,sx,sy,sw,sh, dx,dy,dw,dh);- Let’s take a look at the coordinate sketch:
PS: Do not define
| Description | |
|---|---|
| sy | |
| swidth | |
| sheight | |
| x | |
| y | |
| width | |
| height | |
JavaScript Code
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<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>drawImage()</title>
<style>
body { background: url("./images/bg3.jpg") repeat; }
#canvas { border: 1px solid #aaaaaa; display: block; margin: 50px auto; }
</style>
</head>
<body>
<p id="canvas-warp">
<canvas id="canvas">
你的浏览器居然不支持Canvas？！赶快换一个吧！！
</canvas>
</p>
<script>
window.onload = function(){
var canvas = document.getElementById("canvas");
canvas.width = 800;
canvas.height = 600;
var context = canvas.getContext("2d");
context.fillStyle = "#FFF";
context.fillRect(0,0,800,600);
var img = new Image();
img.src = "./images/20-1.jpg";
img.onload = function(){
context.drawImage(img,200,50);
}
};
</script>
</body>
</html>- Run result:
Create a photo frame: 
Here, we combine clip(), drawImage() and cubic Bezier curve bezierCurveTo() to add a heart-shaped photo frame to the above case~
JavaScript Code
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<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<title>绘制心形相框</title>
<style>
body { background: url("./images/bg3.jpg") repeat; }
#canvas { border: 1px solid #aaaaaa; display: block; margin: 50px auto; }
</style>
</head>
<body>
<p id="canvas-warp">
<canvas id="canvas">
你的浏览器居然不支持Canvas？！赶快换一个吧！！
</canvas>
</p>
<script>
window.onload = function(){
var canvas = document.getElementById("canvas");
canvas.width = 800;
canvas.height = 600;
var context = canvas.getContext("2d");
context.fillStyle = "#FFF";
context.fillRect(0,0,800,600);
context.beginPath();
context.moveTo(400,260);
context.bezierCurveTo(450,220,450,300,400,315);
context.bezierCurveTo(350,300,350,220,400,260);
context.clip();
context.closePath();
var img = new Image();
img.src = "./images/20-1.jpg";
img.onload = function(){
context.drawImage(img,348,240,100,100);
}
};
</script>
</body>
</html>
- Run result:
Isn’t it beautiful? Okay, now that we have finished talking about the most critical masking and image cropping, in fact, drawImage() is also a crucial method in java.awt. Some people say that when making Java game interfaces, as long as you know how to use drawImage(), you can conquer the world with one move~ The same is true in Canvas. The materials provided by artists are basically pictures. At this time, drawImage() is very important for processing pictures. Even basic skills are the most important way to process pictures. 
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