Merge pull request #1791 from AyberkA0/fix/1758-cursor-hotspot

Fix #1758: keep the custom title bar window borderless on Windows

apps/vectorcraft/src/main.rs

@@ -45,6 +45,7 @@ mod printing;
 #[cfg(all(windows, not(target_vendor = "win7")))]
 mod system_fonts;
 mod window;
+mod window_frame;
 mod xwayland;
 
 use vectorcraft_engine::Session;
@@ -62,6 +63,8 @@ struct App {
     graphics_lost: bool,
     /// Frames the UI has run (see [`end_before_teardown`]).
     frames: u64,
+    /// Keeps the custom title bar's window borderless (Windows, #1758).
+    window_frame: Option<window_frame::WindowFrameFn>,
 }
 
 impl eframe::App for App {
@@ -72,6 +75,11 @@ impl eframe::App for App {
         file_access::unconfined(|| self.logic_frame(ctx, frame));
     }
     fn raw_input_hook(&mut self, _ctx: &egui::Context, raw: &mut egui::RawInput) {
+        // winit gives the window its caption back when it changes the window's flags (maximize,
+        // restore, …): take it off again before the frame is laid out (#1758).
+        if let Some(window_frame) = self.window_frame.as_mut() {
+            window_frame();
+        }
         #[cfg(target_os = "macos")]
         if self.app.services.native_menu.is_some() {
             mac_menu::raw_input_hook(raw);
@@ -858,7 +866,9 @@ fn main() -> std::process::ExitCode {
                 // The first frame is due from now (`gpu::watch_first_frame`).
                 #[cfg(feature = "wgpu")]
                 created.ready();
-                Ok(Box::new(App { app, graphics_loss, graphics_lost: false, frames: 0 }))
+                // The content and the pointer stay aligned on Windows (#1758).
+                let window_frame = window_frame::service(cc, custom_titlebar);
+                Ok(Box::new(App { app, graphics_loss, graphics_lost: false, frames: 0, window_frame }))
             }),
         )
     });

apps/vectorcraft/src/window_frame.rs

@@ -0,0 +1,75 @@
+//! Keeps the custom title bar's undecorated window truly borderless on Windows (#1758).
+//!
+//! winit 0.30 gives an undecorated window the `WS_CAPTION | WS_BORDER` styles and hides the
+//! non-client area by spreading the client rect over it (`WM_NCCALCSIZE`). On some systems the
+//! desktop compositor still reserves that frame for the window surface: the content is drawn
+//! offset by the caption and border while the pointer keeps the un-offset client coordinates, so
+//! it no longer points at what is drawn under it (rust-windowing/winit#2419; PhotoCraft fixed the
+//! same in storytold/photocraft#2401). [`service`] strips the two styles and has Windows
+//! recalculate the frame; winit puts them back whenever it changes the window flags (maximize,
+//! restore, …), so the returned guard runs every frame.
+
+/// Run once per frame; a no-op once the window is borderless.
+pub type WindowFrameFn = Box<dyn FnMut()>;
+
+pub use platform::service;
+
+#[cfg(all(windows, feature = "wgpu"))]
+mod platform {
+    use eframe::wgpu::rwh::{HasWindowHandle, RawWindowHandle};
+    use winsafe::{HWND, HwndPlace, POINT, SIZE, co};
+
+    /// A guard that keeps the window borderless each frame, or `None` with the system title bar
+    /// (the window is decorated) or when its handle can't be found.
+    pub fn service(cc: &eframe::CreationContext<'_>, custom_titlebar: bool) -> Option<super::WindowFrameFn> {
+        if !custom_titlebar {
+            return None;
+        }
+        let target = match cc.window_handle().ok()?.as_raw() {
+            RawWindowHandle::Win32(h) => h.hwnd.get(),
+            _ => return None,
+        };
+        let hwnd = find_window(target)?;
+        strip(&hwnd);
+        Some(Box::new(move || strip(&hwnd)))
+    }
+
+    /// The top-level window with the given raw handle: `EnumWindows` hands out real `HWND`s, so
+    /// this needs no `unsafe` to wrap a raw one.
+    fn find_window(target: isize) -> Option<HWND> {
+        let mut found = None;
+        let _ = winsafe::EnumWindows(|hwnd| {
+            if hwnd.ptr() as isize == target {
+                found = Some(hwnd);
+                false
+            } else {
+                true
+            }
+        });
+        found
+    }
+
+    /// Removes `WS_CAPTION` (which includes `WS_BORDER`) and has Windows recalculate the frame;
+    /// the sizing border stays, so edge resizing and snapping keep working.
+    fn strip(hwnd: &HWND) {
+        let style = hwnd.style();
+        let without = style & !(co::WS::CAPTION | co::WS::BORDER);
+        if without.raw() == style.raw() {
+            return;
+        }
+        hwnd.set_style(without);
+        let _ = hwnd.SetWindowPos(
+            HwndPlace::None,
+            POINT::new(),
+            SIZE::new(),
+            co::SWP::FRAMECHANGED | co::SWP::NOMOVE | co::SWP::NOSIZE | co::SWP::NOZORDER | co::SWP::NOACTIVATE,
+        );
+    }
+}
+
+#[cfg(not(all(windows, feature = "wgpu")))]
+mod platform {
+    pub fn service(_cc: &eframe::CreationContext<'_>, _custom_titlebar: bool) -> Option<super::WindowFrameFn> {
+        None
+    }
+}