lc-svg-upload.php

<?php
/*
Plugin Name: SVG Upload
Plugin URI: http://www.lewiscowles.co.uk
Description: Super PHP Plugin to add Full SVG Media support to WordPress, I should live in {$webroot}/wp-content/plugins/ folder ;)
Author: Lewis Cowles
Version: 1.0
Author URI: http://www.lewiscowles.co.uk/
*/
add_action('admin_init', 'add_svg_upload');
function add_svg_upload() {
	add_filter('upload_mimes', function(){
		$mimes['svg'] = 'image/svg+xml';
		return $mimes;
	});
	ob_start();

	add_action('shutdown', function() {
	    $final = '';
	    $ob_levels = count(ob_get_level());
	    for ($i = 0; $i < $ob_levels; $i++) {
	        $final .= ob_get_clean();
	    }
	    echo apply_filters('final_output', $final);
	}, 0);
	add_filter('final_output', function($content) {
		$content = str_replace('<# } else if ( \'image\' === data.type && data.sizes && data.sizes.full ) { #>',
				'<# } else if ( \'svg+xml\' === data.subtype ) { #>
				<img class="details-image" src="{{ data.url }}" draggable="false" />
				<# } else if ( \'image\' === data.type && data.sizes && data.sizes.full ) { #>',
				$content
		);
		$content = str_replace(
			'<# } else if ( \'image\' === data.type && data.sizes ) { #>',
				'<# } else if ( \'svg+xml\' === data.subtype ) { #>
				<div class="centered">
					<img src="{{ data.url }}" class="thumbnail" draggable="false" />
				</div>
			<# } else if ( \'image\' === data.type && data.sizes ) { #>',
				$content
		);
		return $content;
	});
}
/*
 * Logic Breakdown
 * 1) We need the whole page, but only if we are in the backend (hence admin_init hook)
 * 2) We would like to grab all output (ob_start within admin_init as nothing should echo before that, we should not interfere with things that do)
 * 3) We want to grab the content on shutdown, concatenate all output buffers, then filter
 * 4) Search for placeholders which should exist and replace the text
 * Downsides
 * 1) Not permanent fix (for perma fix WP core would need to be editable or native filtering added)
 * 2) A bit resource munchy (it's locked to the admin side, so IMHO who cares)
 * 3) This is just to get SVG into WP core... Luckily the find replace is that simple in /wp-includes/media-template.php (Patch it Mullenweg & Co!)
 */