WordPress的动态粉丝

Typically, a single favicon is used across a whole domain. But there are times you wanna step it up with different favicons depending on context. A website might change the favicon to match the content being viewed. Or a site might allow users to personalize their theme colors, and those preferences are reflected in the favicon. Maybe you’ve seen favicons that attempt to alert the user of some event.

Multiple favicons can technically be managed by hand — Chris has shown us how he uses two different favicons for development and production. But when you reach the scale of dozens or hundreds of variations, it’s time to dynamically generate them.

This was the situation I encountered on a recent WordPress project for a directory of colleges and universities. (I previously wrote about querying nearby locations for the same project.) When viewing a school’s profile, we wanted the favicon to use a school’s colors rather than our default blue, to give it that extra touch.

With over 200 schools in the directory and climbing, we needed to go dynamic. Fortunately, we already had custom meta fields storing data on each school’s visual identity. This included school colors, which were being used in the stylesheet. We just needed a way to apply these custom meta colors to a dynamic favicon.

In this article, I’ll walk you through our approach and some things to watch out for. You can see the results in action by viewing different schools.

SVG is key

Thanks to improved browser support for SVG favicons, implementing dynamic favicons is much easier than days past. In contrast to PNG (or the antiquated ICO format), SVG relies on markup to define vector shapes. This makes them lightweight, scaleable, and best of all, receptive to all kinds of fun.

The first step is to create your favicon in SVG format. It doesn’t hurt to also run it through an SVG optimizer to get rid of the cruft afterwards. This is what we used in the school directory:

Hooking into WordPress

Next, we want to add the favicon link markup in the HTML head. How to do this is totally up to you. In the case of WordPress, it could be added it to the header template of a child theme or echo’d through a wp_head() action.

function ca_favicon() {
  if ( is_singular( 'school' ) ) {
    $post_id = get_the_ID();
    $color = get_post_meta( $post_id, 'color', true );

    if ( isset( $color ) ) {
      $color = ltrim( $color, '#' ); // remove the hash
      echo '<link rel="icon" href="' . plugins_url( 'images/favicon.php?color=' . $color, __FILE__ ) . '" type="image/svg+xml" sizes="any">';
    }
  }
}
add_filter( 'wp_head' , 'ca_favicon' );

Here we’re checking that the post type is school, and grabbing the school’s color metadata we’ve previously stored using get_post_meta(). If we do have a color, we pass it intofavicon.phpthrough the query string.

From PHP to SVG

In a favicon.php file, we start by setting the content type to SVG. Next, we save the color value that’s been passed in, or use the default color if there isn’t one.

Then we echo the large, multiline chunk of SVG markup using PHP’s heredoc syntax (useful for templating). Variables such as $color are expanded when using this syntax.

Finally, we make a couple modifications to the SVG markup. First, classes are assigned to the color-changing elements. Second, a style element is added just inside the SVG element, declaring the appropriate CSS rules and echo-ing the $color.

Instead of a