Add option to “Gallery Settings” section

I want to add a option to the “Gallery settings” (when you insert a gallery into a post).

I once found some code on how to do this, but unfortunately I can’t find it anymore.
I can’t even remenber if it was a hook, but I think it was some hackish stuff 😉

Thx

Thanks to the hint with the multiple galleries plugin from Niall Campbell and thanks to this question How to Add a Custom Colum on Thickbox Media Gallery Tab? (where I got the hook admin_head-media-upload-popup from), I was able to complete the task.

I’ve added an option to add a style attribute to the gallery shortcode.

Here is the complete code:

add_action( 'admin_head-media-upload-popup', 'wpse_53803_script_enqueuer' );

function wpse_53803_script_enqueuer() 
{
    if( $_GET['tab'] == 'gallery' ) 
    {
        ?>
        <script type="text/javascript">
        jQuery(document).ready( function($) {

            // append the table row
            $('#gallery-settings table#basic tbody').append('<tr><th scope="row" class="label"><label><span class="alignleft">Style:</span></label></th><td class="field"><select id="style" name="style"><option value="standard">Standard</option><option value="slideshow">Slideshow</option></select></td></tr>');

            // set our vars
            var $style="", $is_update = false;

            // Select parent editor, read existing gallery data 
            w = wpgallery.getWin();
            editor = w.tinymce.EditorManager.activeEditor;

            if (editor !== null) {
                gal = editor.selection.getNode();

                if (editor.dom.hasClass(gal, 'wpGallery')) {
                    $style = editor.dom.getAttrib(gal, 'title').match(/style=['"]([^'"]+)['"]/i);
                    var $is_update = true;
                    if ($style != null) {
                        $style = $style[1];
                        $('table#basic #style').find('option[value="' + $style + '"]').attr('selected','selected');
                    }
                } else {
                    $('#insert-gallery').show();
                    $('#update-gallery').hide();
                }
            }

            // remove standard onmousedown action
            $('#insert-gallery').attr('onmousedown', '');

            // Insert or update the actual shortcode
            $('#update-gallery, #insert-gallery, #save-all').mousedown(function() {
                var $styleAdd = '';
                if (editor !== null)
                    var orig_gallery = editor.dom.decode(editor.dom.getAttrib(gal, 'title'));
                else
                    var orig_gallery = '';

                // Check which which style is selected
                if($('table#basic #style').val() != 'standard') {
                    $styleAdd = ' style="slideshow"';
                }

                if ($(this).attr('id') == 'insert-gallery') {
                    w.send_to_editor('[gallery' + wpgallery.getSettings() + $styleAdd + ']');
                }

                // Update existing shortcode
                if ($is_update) {
                    if ($styleAdd != '' && orig_gallery.indexOf(' style=") == -1)
                        editor.dom.setAttrib(gal, "title', orig_gallery + $styleAdd);
                    else if (orig_gallery.indexOf(' style=") != -1)
                        editor.dom.setAttrib(gal, "title', orig_gallery.replace(' style="slideshow"', $styleAdd));
                    else
                        editor.dom.setAttrib(gal, 'title', orig_gallery.replace(' style="slideshow"', ''));
                }
            });

        });
        </script>
        <?php
    }
}

It adds style="slideshow" if the slideshow style is selected, otherwise it doesn’t add anything. And it recognizes the set style if you update the gallery, so that the right option is selected.

Thank you!