fix on windows

Author: timon-schelling

desktop/src/window/win/native_handle.rs

@@ -211,7 +211,7 @@ unsafe fn ensure_helper_class() {
 unsafe extern "system" fn main_window_handle_message(hwnd: HWND, msg: u32, wparam: WPARAM, lparam: LPARAM) -> LRESULT {
 	if msg == WM_NCCALCSIZE && wparam.0 != 0 {
 		// When maximized, shrink to visible frame so content doesn't extend beyond it.
-		if unsafe { IsZoomed(hwnd).as_bool() } {
+		if unsafe { IsZoomed(hwnd).as_bool() } && !is_effectively_fullscreen(hwnd) {
 			let params = unsafe { &mut *(lparam.0 as *mut NCCALCSIZE_PARAMS) };
 
 			let dpi = unsafe { GetDpiForWindow(hwnd) };
@@ -366,3 +366,36 @@ unsafe fn calculate_resize_direction(helper: HWND, lparam: LPARAM) -> Option<u32
 		_ => None,
 	}
 }
+
+// Check if the window is effectively fullscreen, meaning it covers the entire monitor.
+// We need to use this heuristic because Windows doesn't provide a way to check for fullscreen state.
+fn is_effectively_fullscreen(hwnd: HWND) -> bool {
+	if hwnd.is_invalid() {
+		return false;
+	}
+
+	let mut view_rect = RECT::default();
+	if unsafe { GetWindowRect(hwnd, &mut view_rect) }.is_err() {
+		return false;
+	}
+
+	let hmon = unsafe { MonitorFromWindow(hwnd, MONITOR_DEFAULTTONEAREST) };
+	if hmon.is_invalid() {
+		return false;
+	}
+
+	let mut monitor_info = MONITORINFO {
+		cbSize: std::mem::size_of::<MONITORINFO>() as u32,
+		..Default::default()
+	};
+	if !unsafe { GetMonitorInfoW(hmon, &mut monitor_info) }.as_bool() {
+		return false;
+	}
+
+	// Allow a tiny tolerance for DPI / rounding issues
+	const EPS: i32 = 1;
+	(view_rect.left - monitor_info.rcMonitor.left).abs() <= EPS
+		&& (view_rect.top - monitor_info.rcMonitor.top).abs() <= EPS
+		&& (view_rect.right - monitor_info.rcMonitor.right).abs() <= EPS
+		&& (view_rect.bottom - monitor_info.rcMonitor.bottom).abs() <= EPS
+}