Merge two animated GIFs with PHP (ImageMagick)

merge-two-gifs.php

<?php

/*
 * This can be used to merge two animated gifs into one. Both GIFs should 
 * have the same size and frame rates. ImageMagick is needed for this to work
 * 
 * Author: Nenad Mitic [email protected]
 * 
 */

function splitToFrames($imagePath, $prefix)
{
    $dirPath = __DIR__ . '/temp';
    $coalesced = (new Imagick($imagePath))->coalesceimages();
    $i = 0;

    while ($coalesced->hasnextimage()) {
        $coalesced->setiteratorindex($i);
        $coalesced->writeimage("$dirPath/$prefix-$i.png");
        $i++;
    }

    $coalesced = null;
    gc_collect_cycles();
}

function mergeFrames($backgroudPrefix, $foregroundPrefix, $amountOfFrames)
{
    $dirPath = __DIR__ . '/temp';

    for ($i = 0; $i < $amountOfFrames; $i++) {
        $out = new Imagick("$dirPath/$backgroudPrefix-$i.png");
        $out->compositeimage(new Imagick("$dirPath/$foregroundPrefix-$i.png"), Imagick::COMPOSITE_DEFAULT, 0, 0);
        $out->setimagecompression(9);
        $out->writeimage();
    }

    $out = null;
    gc_collect_cycles();
}

function createAnimation($prefix, $outputName, $amountOfFrames)
{
    $dirPath = __DIR__ . '/temp';
    $out = new Imagick();
    $out->setformat('gif');

    for ($i = 0; $i < $amountOfFrames; $i++) {
        $out->addimage(new Imagick("$dirPath/$prefix-$i.png"));
        $out->setimagedelay(4);
        $out->setimageiterations(1);
    }

    $out->writeimages("$dirPath/$outputName.gif", true);
    $out = null;
    gc_collect_cycles();
}

$background = __DIR__ . '/src/back.gif';
$front = __DIR__ . '/src/front.gif';

splitToFrames($background, 'back');
$framesCount = count(glob(__DIR__ . '/temp/back-*.png'));
splitToFrames($front, 'front');
mergeFrames('back', 'front', $framesCount);
createAnimation('back', 'out', $framesCount);