Optimizing startup time of Gtk4.0 apps on RPI Zero?

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I recognize that the RPI Zero is a very weak computer by modern standards, but is there anything that I can do to make the GTK4 apps I write startup faster on it? The GTK4 example on the website takes about 14 seconds to open a window on it

#include <gtk/gtk.h>

static void
activate (GtkApplication* app,
          gpointer        user_data)
{
  GtkWidget *window;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Window");
  gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
  gtk_window_present (GTK_WINDOW (window));
}

int
main (int    argc,
      char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}

For comparison (and in no way apples to apples), an SDL2 program takes ~6 seconds, to open up a blank window, a comparable python tkinter app takes 3, and just working directly with X11 is instant.

#include <X11/Xlib.h>
#include <stdio.h>
#include <stdlib.h> // For exit function

int main() {
    Display *display;
    Window window;
    XEvent event;
    int screen;

    // Open connection to the X server
    display = XOpenDisplay(NULL);
    if (display == NULL) {
        fprintf(stderr, "Cannot open display\n");
        exit(1);
    }

    screen = DefaultScreen(display);


    window = XCreateSimpleWindow(display, RootWindow(display, screen), 10, 10, 800, 600, 1,
                                 BlackPixel(display, screen), WhitePixel(display, screen));


    XSelectInput(display, window, ExposureMask | KeyPressMask);


    XMapWindow(display, window);


    while (1) {
        XNextEvent(display, &event);
        
        // Break out of the loop if the user presses any key
        if (event.type == KeyPress)
            break;
    }


    XCloseDisplay(display);
    return 0;
}

I know GTK is doing a lot for me, so I don’t expect things to be instant, and it’s amazing that it even works on an RPI Zero to begin with. But I just want to make sure I didn’t miss anything when looking to see if things could be made faster.

[jfrancis (Jason Francis)]

Hello, most likely you want to profile the library to see where most of the time is being spent during startup. But I can guess some things which all take time to load:

• Fonts
• Icons
• Translations (.mo files)
• Input methods
• Cursors
• XSettings
• CSS (even for the default theme)
• GL shaders (I can’t remember if RPI Zero supports this)

That simple X application has none of these, so probably you can see why it goes faster. You may also want to profile against Wayland to see if that has any effect on the speed, the X11 startup may require more server round-trips.