Gtk3FileDialog.cs

using System;
using System.Runtime.InteropServices;
using UnityEngine;

namespace NativeFileBrowser
{
    public static class Gtk3FileDialog
    {
        // Steam's runtime does not provide gtk4 (which is nicer), so, use gtk3, which *is* provided by steam
        // TODO: Somehow check if this is actually loading Steam's version and not the system one?
        private const string So = "libgtk-3.so.0";

        [DllImport(So)]
        private static extern void gtk_init(IntPtr argc, IntPtr argv);

        [DllImport(So)]
        private static extern int gtk_main_iteration_do(int blocking);

        // gtk_file_chooser_dialog_new is a varargs function, hardcode one set of buttons
        [DllImport(So)]
        private static extern IntPtr gtk_file_chooser_dialog_new([MarshalAs(UnmanagedType.LPUTF8Str)] string title, IntPtr parent, int action, [MarshalAs(UnmanagedType.LPUTF8Str)] string buttonName, int responseType, IntPtr zero);

        [DllImport(So)]
        private static extern void gtk_file_chooser_set_select_multiple(IntPtr dialog, int selectMultiple);

        [DllImport(So)]
        private static extern void gtk_file_chooser_set_current_folder(IntPtr dialog, [MarshalAs(UnmanagedType.LPUTF8Str)] string folder);

        [DllImport(So)]
        private static extern IntPtr gtk_file_chooser_get_filenames(IntPtr dialog);

        [DllImport(So)]
        private static extern void gtk_file_chooser_add_filter(IntPtr chooser, IntPtr filter);

        [DllImport(So)]
        private static extern IntPtr gtk_file_filter_new();

        [DllImport(So)]
        private static extern void gtk_file_filter_set_name(IntPtr filter, [MarshalAs(UnmanagedType.LPUTF8Str)] string name);

        [DllImport(So)]
        private static extern void gtk_file_filter_add_pattern(IntPtr filter, [MarshalAs(UnmanagedType.LPUTF8Str)] string pattern);

        [DllImport(So)]
        private static extern void gtk_file_filter_add_mime_type(IntPtr filter, [MarshalAs(UnmanagedType.LPUTF8Str)] string mimeType);

        [DllImport(So)]
        private static extern uint g_slist_length(IntPtr list);

        [DllImport(So)]
        private static extern IntPtr g_slist_nth_data(IntPtr list, uint n);

        [DllImport(So)]
        private static extern void g_free(IntPtr mem);

        [DllImport(So)]
        private static extern void g_slist_free(IntPtr mem);

        [DllImport(So)]
        private static extern int gtk_dialog_run(IntPtr dialog);

        [DllImport(So)]
        private static extern int gtk_widget_destroy(IntPtr widget);

        static Gtk3FileDialog()
        {
            gtk_init(IntPtr.Zero, IntPtr.Zero);
        }

        public static string[] Pick(FileBrowserSettings settings)
        {
            var action = settings.DialogKind == DialogKind.File ? 0 : 2;
            const int accept = -3;
            var dialog = gtk_file_chooser_dialog_new(settings.Title, IntPtr.Zero, action, "Select", accept, IntPtr.Zero);
            if (settings.MultiSelectKind == MultiSelectKind.Multiple)
            {
                gtk_file_chooser_set_select_multiple(dialog, 1);
            }
            if (settings.InitialFolder != null)
            {
                gtk_file_chooser_set_current_folder(dialog, settings.InitialFolder);
            }
            if (settings.FileExtensionFilters != null)
            {
                foreach (var filterSetting in settings.FileExtensionFilters)
                {
                    var filter = gtk_file_filter_new();
                    if (filterSetting.Name != null)
                    {
                        var name = filterSetting.Name;
                        // windows automatically appends the pattern, do the same here
                        if (filterSetting.Patterns != null)
                            name += $" ({string.Join(", ", filterSetting.Patterns)})";
                        gtk_file_filter_set_name(filter, name);
                    }
                    if (filterSetting.Patterns != null)
                        foreach (var pattern in filterSetting.Patterns)
                            gtk_file_filter_add_pattern(filter, pattern);
                    if (filterSetting.MimeTypes != null)
                        foreach (var pattern in filterSetting.MimeTypes)
                            gtk_file_filter_add_mime_type(filter, pattern);
                    gtk_file_chooser_add_filter(dialog, filter);
                }
            }
            var res = gtk_dialog_run(dialog);
            string[] result;
            if (res == accept)
            {
                var gslist = gtk_file_chooser_get_filenames(dialog);
                result = new string[g_slist_length(gslist)];
                for (var i = 0u; i < result.Length; i++)
                {
                    var filename = g_slist_nth_data(gslist, i);
                    result[i] = Marshal.PtrToStringUTF8(filename);
                    g_free(filename);
                }
                g_slist_free(gslist);
            }
            else
            {
                result = Array.Empty<string>();
            }

            gtk_widget_destroy(dialog);

            // calling main_iteration_do is required to close the window once accepted
            UpdateObject.EnsureOpen();

            return result;
        }

        private class UpdateObject : MonoBehaviour
        {
            private static UpdateObject _instance;

            private void Update() => gtk_main_iteration_do(0);

            public static void EnsureOpen()
            {
                if (!_instance) _instance = new GameObject(nameof(Gtk3FileDialog)).AddComponent<UpdateObject>();
            }
        }
    }
}