How to use html canvas to intercept rounded images

In the past we could only capture images through other screenshot tools. The functions of modern browsers have become more and more powerful. With the gradual popularization of H5, the browser itself can take screenshots. html2canvas is such a front-end plug-in. Its principle is to draw Dom nodes in Canvas. Although it is very convenient, it has the following limitations:

This article mainly introduces the relevant information about the solution for html2canvas screenshots that cannot capture rounded images. The editor thinks it is quite good. Now I will share it with you and give it as a reference. . Let’s follow the editor to take a look, I hope it can help everyone.

• iframe is not supported

• cross-domain images are not supported

• cannot be used in browser plug-ins Use

• SVG images are not supported on some browsers

• Flash is not supported

• Not supported Ancient browsers and IE, if you want to confirm whether a certain browser is supported, you can use it to visit http://deerface.sinaapp.com/ and try:)

Because of my The usage scenario is very simple, record the exception information, and the exception page is also defined by yourself, then html2canvas is enough to use.

The first time I use html2canvas, the purpose is to take a screenshot of the entire page and generate a picture for the user to save

Let’s first take a look at what the HTML rendering looks like

You can see from the image rendered by HTML that the above image has a rounded corner effect, but when I use html2canvas to convert the image, I find that the rounded corner effect of the image does not fail. .

became like this. After thinking about many solutions, I finally decided to make the rounded corners at the back into a background image. The background of the middle circle is transparent, and then it is overlaid on the original image through absolute positioning, which is equivalent to a mask effect.

Of course, the DOM node of the mask image must be below the image that requires rounded corners, similar to

<p class="avatar_img fl"><p class="avatar_img fl"> 
     <img  class="avatar_pp fl lazy"  src="/static/imghwm/default1.png"  data-src="" id="   id="you"  / alt="How to use html canvas to intercept rounded images" ><!--需要圆角的原始图片-->
     <img  class="img-responsive lazy"  src="/static/imghwm/default1.png"  data-src="/template/images/avatar.png"      style="max-width:90%" alt="How to use html canvas to intercept rounded images" ><!--遮罩图片-->
</p>

The generated image will look normal

<p class="avatar_img fl"><p class="avatar_img fl"> 
     <img  class="avatar_pp fl lazy"  src="/static/imghwm/default1.png"  data-src="" id="   id="you"  / alt="How to use html canvas to intercept rounded images" ><!--需要圆角的原始图片-->
     <img  class="img-responsive lazy"  src="/static/imghwm/default1.png"  data-src="/template/images/avatar.png"      style="max-width:90%" alt="How to use html canvas to intercept rounded images" ><!--遮罩图片-->
</p>

Copy code

The code is as follows:

<a href="<a href=" 
<img  src="/static/imghwm/default1.png"  data-src="<a href="  class="lazy" " alt="How to use html canvas to intercept rounded images" >http://www.teaxia.com/wp-content/uploads/2018/01/2.jpg"><img  src="/static/imghwm/default1.png"  data-src="<a href="  class="lazy" </a alt="How to use html canvas to intercept rounded images" >  
http://www.teaxia.com/wp-content/uploads/2018/01/2-169x300.jpg</a>" alt="" width="169" height="300" 
srcset="<a href=" 
http://www.teaxia.com/wp-content/uploads/2018/01/2-169x300.jpg</a> 169w, 
<a href=" 
http://www.teaxia.com/wp-content/uploads/2018/01/2.jpg</a> 377w" 
sizes="(max-width: 169px) 100vw, 169px" /></a>

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