Create image thumb on given size without effection original aspect ratio

generate-image-thumb.php

<?php
function generate_thumb($source_image_path, $thumbnail_image_path, $result_width, $result_height) {
    if(!file_exists($source_image_path)) {
        return false;
    }

    if(!getimagesize($source_image_path)) {
        return false;;
    }

    list(
        $source_image_width,
        $source_image_height,
        $source_image_type
    ) = getimagesize($source_image_path);

    switch ($source_image_type) {
        case IMAGETYPE_GIF:
            $source_gd_image = imagecreatefromgif($source_image_path);
            break;
        case IMAGETYPE_JPEG:
            $source_gd_image = imagecreatefromjpeg($source_image_path);
            break;
        case IMAGETYPE_PNG:
            $source_gd_image = imagecreatefrompng($source_image_path);
            break;
        default:
            return false;
    }

    $source_aspect_ratio = $source_image_width / $source_image_height;
    $thumbnail_aspect_ratio = $result_width / $result_height;

    if ($source_image_width <= $result_width &&
        $source_image_height <= $result_height) {
        $thumbnail_image_width = $source_image_width;
        $thumbnail_image_height = $source_image_height;
    } elseif ($thumbnail_aspect_ratio > $source_aspect_ratio) {
        $thumbnail_image_width = (int) ($result_height * $source_aspect_ratio);
        $thumbnail_image_height = $result_height;
    } else {
        $thumbnail_image_width = $result_width;
        $thumbnail_image_height = (int) ($result_width / $source_aspect_ratio);
    }

    $thumbnail_gd_image = imagecreatetruecolor($thumbnail_image_width, $thumbnail_image_height);

    imagecopyresampled($thumbnail_gd_image, $source_gd_image, 0, 0, 0, 0, $thumbnail_image_width, $thumbnail_image_height, $source_image_width, $source_image_height);

    imagejpeg($thumbnail_gd_image, $thumbnail_image_path, 90);
    imagedestroy($source_gd_image);
    imagedestroy($thumbnail_gd_image);
    return true;
}