How to solve the problem that template svg is not displayed in php

In web development, we often need to use images, and SVG (Scalable Vector Graphics) is a very useful format that can adaptively scale without distortion, so it is increasingly favored by developers. . There are also many libraries in PHP that support the use of SVG images, but sometimes you encounter the problem that SVG images cannot be displayed properly. This article will introduce one of the situations - when using the template engine to load SVG images in PHP, the problem that the SVG images cannot be displayed occurs, and provide a solution.

Problem description

Use the template engine to load SVG images in PHP, but they cannot be displayed normally on the page and only a blank area appears.

Cause of the problem

The file structure of the SVG image is different from the ordinary HTML file structure, which includes special attributes such as XML declaration and namespace. These attributes will be recognized as tags by the template engine, causing problems when rendering, causing the SVG image to not display properly.

Solution

Option 1: Turn off the parsing of SVG images by the template engine

You can disable the parsing of SVG images by setting it in the configuration file of the template engine, thereby Avoid the problem of SVG not being displayed properly due to parsing errors.

Taking Smarty as an example, you can add the following configuration in the configuration file:

// 关闭对SVG图像的解析
$smarty->security_settings['allowed_tags'] = array_diff($smarty->security_settings['allowed_tags'], array('svg'));
$smarty->security_settings['allowed_modifiers'] = array_diff($smarty->security_settings['allowed_modifiers'], array('svg'));

Solution 2: Escape SVG tag

Add the escape character "\ in front of the SVG tag ” can prevent the template engine from parsing it into HTML tags, thereby avoiding the problem of SVG images not being displayed properly.

For example, convert the following code:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
  <path d="M256 22.4C131.4 22.4 27.2 126.6 27.2 251.2S131.4 480 256 480s228.8-104.2 228.8-228.8S380.6 22.4 256 22.4zM256 406.2c-87.9 0-159.8-71.8-159.8-159.8s71.8-159.8 159.8-159.8 159.8 71.8 159.8 159.8S343.9 406.2 256 406.2z"/>
</svg>

to the following code:

\<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
  \<path d="M256 22.4C131.4 22.4 27.2 126.6 27.2 251.2S131.4 480 256 480s228.8-104.2 228.8-228.8S380.6 22.4 256 22.4zM256 406.2c-87.9 0-159.8-71.8-159.8-159.8s71.8-159.8 159.8-159.8 159.8 71.8 159.8 159.8S343.9 406.2 256 406.2z"/>
\</svg>

This way the template engine will not recognize the SVG tags as HTML tags and will render correctly SVG image.

Summary

When using SVG images in PHP, there may be problems that cannot be displayed properly, especially when using template engines. This article describes two solutions: turning off the template engine's parsing of SVG images and escaping SVG tags. When we encounter this problem, we can choose the corresponding solution according to the specific situation.

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