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[Win32] GTK partially freezes the desktop under specific circumstances in a mixed-DPI setup

Steps to reproduce

  1. Compile the provided MVE and ensure it is linked with the provided manifest.
  2. Set two adjacent monitors up. Set one to 200% scale and the other to 100% scale.
  3. Slowly drag the window from one monitor to the other.
  4. Your desktop should partially freeze, blocking some types of user input. You can unfreeze it by closing the app through Task Manager.

MVE

gtk-scaling-mve.c (Main source code)

#include <gtk/gtk.h>
#include <windows.h>

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

	button = gtk_button_new_with_label("click me!");
	gtk_widget_set_margin_top(button, 12);
	gtk_widget_set_margin_bottom(button, 12);
	gtk_widget_set_margin_start(button, 12);
	gtk_widget_set_margin_end(button, 12);

	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_set_child(GTK_WINDOW(window), button);
	gtk_window_present(GTK_WINDOW(window));
}

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

	SetEnvironmentVariableA("GTK_CSD", "0");

	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;
}

app.manifest (This is needed to enable per-monitor DPI scaling)

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
  <asmv3:application>
    <asmv3:windowsSettings>
      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true</dpiAware>
      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
    </asmv3:windowsSettings>
  </asmv3:application>
</assembly>

Current behavior

The window remains frozen in place. Certain inputs are blocked on other windows or register incorrectly (for example, attempting to open a dropdown in Task Manager doesn't work).

Expected outcome

GTK should not freeze.

Version information

  • GTK version: 4.16.5 (current version provided by gvsbuild)
    • configuration: debug-optimized

Additional information

Here's what the desktop looks like when I trigger the freeze: F10DBAE6-AF35-4AC5-B144-93D277D39E0C

Nothing of interest is printed to the terminal before the crash, even if I set G_MESSAGES_DEBUG=1.

System information

  • OS: Windows 11 Home (23H2, OS Build 22631.4460)
  • Graphics: Intel UHD Graphics
  • Monitors: I have two monitors:
    • Laptop screen: 2256x1024, 200% scaling
    • Monitor: 1920x1080, 100% scaling