theme gallery as default, simplest gallery only in some posts

in case someone wants to use imageflow from simplest gallery just like me, here is the code of sg-imageflow.php I altered. You don’t need to install simple gallery at all this way. only the altered imageflow plugin.

imageflow gallery is used only if you add type in the shortcode:
[gallery type="imageflow" ]

sg-imageflow.php:

<?php
/*
Plugin Name: Imageflow for Simplest Gallery
Version: 1.1
Plugin URI: https://www.simplestgallery.com/add-ons/
Description: Display your WordPress galleries as an Imageflow with reflected images. Requires the "Simplest Gallery" plugin (adds a new gallery style to it).
Author: Cristiano Leoni
Author URI: https://www.linkedin.com/pub/cristiano-leoni/2/b53/34

# This file is UTF-8 - These are accented Italian letters aeiou

Includes software by Finn Rudolph, Ralf Hettinger, Richard Davey, Monte Ohrt et al.

*/

/*

    History
   + 1.1 2014-06-26	Fix to avoid problems in the page (div ID renamed and line breaks removed)
   + 1.0 2013-04-29	First working version
*/

/** plugin code **/
function imageflow_gallery_enqueue() {
	if (isTimeToLoadImageflowGallery()) {
		global $wp_styles;
		$imageflow_gallery_plugin_prefix = WP_PLUGIN_URL . '/' . basename(dirname(__FILE__));

			// add javascript to head

			wp_enqueue_script('imageflow_gallery-1.2.1', ($imageflow_gallery_plugin_prefix.'/imageflow/imageflow.js'), false, '1.2.1');
			// add css to head
			wp_enqueue_style('imageflow_gallery_style-1.2.1', ($imageflow_gallery_plugin_prefix . '/imageflow/imageflow.css'));

	}
}

function imageflow_gallery_shortcode($output, $attr) {
	if (!isTimeToLoadImageflowGallery()) return $output;
	if (isset($attr['type']) && $attr['type']=="imageflow")
	{
	global $post, $wp_locale;

	// We're trusting author input, so let's at least make sure it looks like a valid orderby statement
	if ( isset( $attr['orderby'] ) ) {
		$attr['orderby'] = sanitize_sql_orderby( $attr['orderby'] );
		if ( !$attr['orderby'] ) {
			unset( $attr['orderby'] );
		}
	}

	extract(shortcode_atts(array(
		'order'      => 'ASC',
		'orderby'    => 'menu_order ID',
		'id'         => $post->ID,
		'itemtag'    => '',
		'icontag'    => '',
		'captiontag' => '',
		'columns'    => 3,
		'size'       => 'thumbnail',
		'include'    => '',
		'exclude'    => ''
	), $attr));

	$image_size			= get_option('image_size', 'medium');
	$ignore_columns		= get_option('ignore_columns', 'no');
	$thumbnail_caption	= get_option('thumbnail_caption', 'show');

	$id = intval($id);
	if ( 'RAND' == $order ) {
		$orderby = 'none';
	}

	if ( !empty($include) ) {
		$include = preg_replace( '/[^0-9,]+/', '', $include );
		$_attachments = get_posts( array('include' => $include, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );
		$attachments = array();
		foreach ( $_attachments as $key => $val ) {
			$attachments[$val->ID] = $_attachments[$key];
		}
	} elseif ( !empty($exclude) ) {
		$exclude = preg_replace( '/[^0-9,]+/', '', $exclude );
		$attachments = get_children( array('post_parent' => $id, 'exclude' => $exclude, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );
	} else {
		$attachments = get_children( array('post_parent' => $id, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby) );
	}

	if ( empty($attachments) ) {
		return '';
	}

	if ( is_feed() ) {
		$output = "\n";
		foreach ( $attachments as $att_id => $attachment ) {
			$output .= wp_get_attachment_link($att_id, $size, true) . "\n";
		}
		return $output;
	}

	$output = makeImageflowGalleryForPCandTablets($attachments, $thumbnail_caption, $id, $image_size, $ignore_columns, $columns);

	return $output;
	}
}

function makeImageflowGalleryForPCandTablets($attachments, $thumbnail_caption, $id, $image_size, $ignore_columns, $columns){

	$html_id="ImageFlow_".$id;
	$pluginpath = WP_PLUGIN_URL . '/' . basename(dirname(__FILE__));
	$siteurl = get_bloginfo('url');

	$startShot = intval(count($attachments)/2)+1;
	$showDesc = FALSE;
	$reflectColor = 'ffffff';

          $output .= '
<div id="imageflow_left"><script type="text/javascript" defer="defer">
	domReady(function() {
		var instance1 = new ImageFlow();
		instance1.init({
			ImageFlowID:\''.$html_id.'\'
			, onClick: \'\'
			, preloadImages: false
			, reflectionGET: \'&bgc='.$reflectColor.'\'
			, startID: '.$startShot.'
		});
	});
</script><div id="'.$html_id.'" class="imageflow">';

	$count=0;
	foreach ($attachments as $id => $attachment) {
		$im = wp_get_attachment_image_src($id, $size=$image_size, $icon = false);
		$htmlcaption=wptexturize(trim($attachment->post_title));

		$reflect_url = $pluginpath.'/reflect2.php?img='.str_replace(sgif_selfServer(),'',$im[0]).'&bgc='.$reflectColor;
		$output .= '<img src="'.$reflect_url.'" longdesc="'.($showDesc?$htmlcaption:'').'" alt="'.($showDesc?$htmlcaption:'').'" title="'.$htmlcaption.'" />';

		$count++;
	}
	$output .= '</div><!-- /imageflow_left -->';

	return $output;	

}

function sgif_selfServer() {
 $s = empty($_SERVER["HTTPS"]) ? '' : ($_SERVER["HTTPS"] == "on") ? "s" : "";
 $protocol = sgif_strleft(strtolower($_SERVER["SERVER_PROTOCOL"]), "/").$s;
 $port = ($_SERVER["SERVER_PORT"] == "80") ? "" : (":".$_SERVER["SERVER_PORT"]);
 return $protocol."://".$_SERVER['SERVER_NAME'].$port;
}

function sgif_strleft($s1, $s2) {
 return substr($s1, 0, strpos($s1, $s2));
}

function isTimeToLoadImageflowGallery(){
	$show_in_pages = (get_option('show_in_pages', 'yes') === 'yes');
	return (!is_admin() AND ($show_in_pages OR is_single() OR is_feed()));
}

add_action('wp_enqueue_scripts', 'imageflow_gallery_enqueue');
//Shortcode
add_filter('post_gallery', 'imageflow_gallery_shortcode', 10, 2);

?>