Skip to content

Win32: Migrate to Per-Monitor V2 Thread-based DPI awareness #266

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
prokopyl wants to merge 4 commits into
base: master
Choose a base branch
from
Open

Win32: Migrate to Per-Monitor V2 Thread-based DPI awareness #266

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
6c1c23a
wip
prokopyl Jun 13, 2026
cfab555
fix unused
prokopyl Jun 13, 2026
7845dba
Fix initial DPI change event not firing
prokopyl Jun 13, 2026
ec69a7b
Remove unsupported const
prokopyl Jun 13, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
160 changes: 62 additions & 98 deletions src/win/window.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,8 +9,6 @@ use windows_sys::Win32::{
WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MOUSEHWHEEL, WM_MOUSEMOVE, WM_MOUSEWHEEL,
WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR, WM_SETFOCUS, WM_SIZE, WM_SYSCHAR,
WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TIMER, WM_USER, WM_XBUTTONDOWN, WM_XBUTTONUP,
WS_CAPTION, WS_CHILD, WS_CLIPSIBLINGS, WS_MAXIMIZEBOX, WS_MINIMIZEBOX, WS_POPUPWINDOW,
WS_SIZEBOX, WS_VISIBLE,
},
},
};
Expand Down Expand Up @@ -42,7 +40,7 @@ use crate::wrappers::win32::cursor::SystemCursor;
use crate::gl::GlContext;
use crate::wrappers::win32::window::*;
use crate::wrappers::win32::{
ole_initialize, run_thread_message_loop_until, set_process_per_monitor_dpi_aware, Rect,
ole_initialize, run_thread_message_loop_until, Dpi, DpiAwarenessContext, Rect, WindowStyle,
};

#[allow(non_snake_case)]
Expand Down Expand Up @@ -126,50 +124,36 @@ impl WindowImpl for BaseviewWindow {

self._keyboard_hook.set(Some(hook::init_keyboard_hook(hwnd)));

// Only works on Windows 10 unfortunately.
set_process_per_monitor_dpi_aware();

// Now we can get the actual dpi of the window.
let new_size = if let WindowScalePolicy::SystemScaleFactor = self.window_state.scale_policy
{
// Only works on Windows 10 unfortunately.
let dpi = window.get_dpi()?;
let scale_factor = dpi as f64 / 96.0;

let current_scale_factor = window_state.current_scale_factor.get();
let dpi = window.get_dpi()?;
let mut dpi_changed = false;

if dpi != window_state.current_dpi.get() {
window_state.current_dpi.set(dpi);
dpi_changed = true;

// If the user's requested initial size was in system-scaled logical pixels
if let WindowScalePolicy::SystemScaleFactor = self.window_state.scale_policy {
// We cannot create a window in "logical" pixels, and we can't DPI-scale to physical pixels because we
// have no way to know where the window will end up.
// So, at window creation, we assume a DPI=96, and if it ends up wrong, we resize the window
// to the actual logical size the user desired.
let new_size = WindowInfo::from_logical_size(self.initial_size, dpi.scale_factor())
.physical_size();

if current_scale_factor != scale_factor {
window_state.current_scale_factor.set(scale_factor);

let new_size =
WindowInfo::from_logical_size(self.initial_size, scale_factor).physical_size();
// Preemptively update so a synchronous WM_SIZE from SetWindowPos below
// doesn't also emit Resized.
window_state.current_size.set(new_size);

Some(new_size)
} else {
None
window.resize_and_activate(new_size, dpi)?;
}
} else {
None
};
}

let drop_target = ComObject::new(DropTarget::new(Rc::downgrade(window_state)));
self._drop_target.set(Some(drop_target.clone()));

ole_initialize()?;
window.register_drag_drop(drop_target.as_interface())?;

if let Some(new_size) = new_size {
// Windows makes us resize the window manually. This will trigger another `WM_SIZE` event,
// which we can then send the user the new scale factor.
window.resize_and_activate(new_size, window_state.dw_style)?;

// Send an initial Resized event so users get the correct scale factor and physical size.
self.window_state.send_resized(self.initial_size);
}

#[cfg(feature = "opengl")]
if let Some(gl_config) = self.gl_config.clone() {
let mut handle = Win32WindowHandle::empty();
Expand All @@ -191,6 +175,11 @@ impl WindowImpl for BaseviewWindow {
};
*window_state.handler.borrow_mut() = Some(handler);

if dpi_changed {
// Send an initial Resized event so users get the correct scale factor and physical size.
self.window_state.send_resized();
}

Ok(())
}

Expand Down Expand Up @@ -404,43 +393,36 @@ unsafe fn wnd_proc_inner(

window_state.current_size.set(new_size);

WindowInfo::from_physical_size(new_size, window_state.current_scale_factor.get())
WindowInfo::from_physical_size(new_size, window_state.current_scale_factor())
};

window_state.handle_event(Event::Window(WindowEvent::Resized(new_window_info)));

None
}
WM_DPICHANGED => {
let new_rect = Rect((lparam as *const RECT).read());
let suggested_nc_rect = Rect((lparam as *const RECT).read());
let dpi = Dpi((wparam & 0xFFFF) as u16 as u32);

let current_size = window_state.current_size.get();
let new_size = new_rect.size();
let dpi_ctx = DpiAwarenessContext::new().unwrap();
let style = window.get_style().unwrap();
let suggested_rect =
dpi_ctx.nc_area_to_client_area(suggested_nc_rect, style, dpi).unwrap();

let mut changed = current_size != new_size;
let new_size = suggested_rect.size();

if let WindowScalePolicy::SystemScaleFactor = window_state.scale_policy {
let dpi = (wparam & 0xFFFF) as u16 as u32;
let scale_factor = dpi as f64 / 96.0;
let changed = window_state.current_size.get() != new_size
|| window_state.current_dpi.get() != dpi;

changed |= window_state.current_scale_factor.get() != scale_factor;

window_state.current_scale_factor.set(scale_factor);
}
window_state.current_dpi.set(dpi);
window_state.current_size.set(new_size);

// Windows makes us resize the window manually. This however will not send a WM_SIZE event,
// hence why we are notifying the window handler manually below.
let _ = window.set_nc_rect(new_rect);
let _ = window.set_nc_rect(suggested_nc_rect);

if changed {
// FIXME: this confuses NC size and client size!
window_state.current_size.set(new_size);

let new_window_info = WindowInfo::from_physical_size(
new_size,
window_state.current_scale_factor.get(),
);
window_state.handle_event(Event::Window(WindowEvent::Resized(new_window_info)));
window_state.send_resized();
}

None
Expand Down Expand Up @@ -482,15 +464,14 @@ pub(super) struct WindowState {
/// GWLP_USERDATA) } as *const WindowState`.
pub hwnd: HWND,
current_size: Cell<PhySize>,
current_scale_factor: Cell<f64>,
current_dpi: Cell<Dpi>, // None if in non-system scale policy
keyboard_state: RefCell<KeyboardState>,
mouse_button_counter: Cell<usize>,
mouse_was_outside_window: Cell<bool>,
cursor_icon: Cell<MouseCursor>,
// Initialized late so the `Window` can hold a reference to this `WindowState`
handler: RefCell<Option<Box<dyn WindowHandler>>>,
scale_policy: WindowScalePolicy,
dw_style: u32,

/// Tasks that should be executed at the end of `wnd_proc`. This is needed to avoid mutably
/// borrowing the fields from `WindowState` more than once. For instance, when the window
Expand All @@ -504,21 +485,17 @@ pub(super) struct WindowState {
}

impl WindowState {
pub fn new(
hwnd: HWND, current_size: PhySize, scaling: f64, scale_policy: WindowScalePolicy,
style_flags: u32,
) -> Self {
pub fn new(hwnd: HWND, current_size: PhySize, scale_policy: WindowScalePolicy) -> Self {
Self {
hwnd,
current_scale_factor: scaling.into(),
current_dpi: Dpi::default().into(),
current_size: current_size.into(),
keyboard_state: RefCell::new(KeyboardState::new()),
mouse_button_counter: Cell::new(0),
mouse_was_outside_window: true.into(),
cursor_icon: Cell::new(MouseCursor::Default),
handler: RefCell::new(None),
scale_policy,
dw_style: style_flags,

deferred_tasks: RefCell::new(VecDeque::with_capacity(4)),

Expand Down Expand Up @@ -547,19 +524,22 @@ impl WindowState {
}

pub(super) fn window_info(&self) -> WindowInfo {
WindowInfo::from_physical_size(self.current_size.get(), self.current_scale_factor.get())
WindowInfo::from_physical_size(self.current_size.get(), self.current_scale_factor())
}

fn current_scale_factor(&self) -> f64 {
match self.scale_policy {
WindowScalePolicy::ScaleFactor(scale) => scale,
WindowScalePolicy::SystemScaleFactor => self.current_dpi.get().scale_factor(),
}
}

pub(super) fn keyboard_state(&self) -> Ref<'_, KeyboardState> {
self.keyboard_state.borrow()
}

fn send_resized(&self, logical_size: Size) {
let window_info =
WindowInfo::from_logical_size(logical_size, self.current_scale_factor.get());
self.current_size.set(window_info.physical_size());

self.handle_event(Event::Window(WindowEvent::Resized(window_info)));
fn send_resized(&self) {
self.handle_event(Event::Window(WindowEvent::Resized(self.window_info())));
}

/// Handle a deferred task as described in [`Self::deferred_tasks`].
Expand All @@ -568,11 +548,11 @@ impl WindowState {
WindowTask::Resize(size) => {
// `self.window_info` will be modified in response to the `WM_SIZE` event that
// follows the `SetWindowPos()` call
let scaling = self.current_scale_factor.get();
let window_info = WindowInfo::from_logical_size(size, scaling);
let dpi = self.current_dpi.get();
let window_info = WindowInfo::from_logical_size(size, dpi.scale_factor());
let new_size = window_info.physical_size();

window.resize_and_activate(new_size, self.dw_style).unwrap();
window.resize_and_activate(new_size, dpi).unwrap();
}
WindowTask::Focus => window.set_focus().unwrap(),
}
Expand Down Expand Up @@ -631,42 +611,26 @@ impl Window<'_> {
{
let title = HSTRING::from(options.title);

let scaling = match options.scale {
let scaling_factor = match options.scale {
WindowScalePolicy::SystemScaleFactor => 1.0,
WindowScalePolicy::ScaleFactor(scale) => scale,
};

let current_size = WindowInfo::from_logical_size(options.size, scaling).physical_size();
let mut rect = Rect::from(current_size);
let window_size =
WindowInfo::from_logical_size(options.size, scaling_factor).physical_size();

let flags = if parented {
WS_CHILD | WS_VISIBLE
} else {
WS_POPUPWINDOW
| WS_CAPTION
| WS_VISIBLE
| WS_SIZEBOX
| WS_MINIMIZEBOX
| WS_MAXIMIZEBOX
| WS_CLIPSIBLINGS
};
let style = if parented { WindowStyle::parented() } else { WindowStyle::embedded() };
let dpi_ctx = DpiAwarenessContext::new().unwrap();

if !parented {
rect = rect.client_area_to_nc_area(flags).unwrap();
}
let rect =
dpi_ctx.client_area_to_nc_area(window_size.into(), style, Dpi::default()).unwrap();

let is_open = Rc::new(Cell::new(true));

let parent_handle = ParentHandle { is_open: is_open.clone() };

let initializer = move |hwnd: HWnd| {
let window_state = Rc::new(WindowState::new(
hwnd.as_raw(),
current_size,
scaling,
options.scale,
flags,
));
let window_state = Rc::new(WindowState::new(hwnd.as_raw(), window_size, options.scale));

BaseviewWindow {
window_state,
Expand All @@ -683,7 +647,7 @@ impl Window<'_> {
};

let hwnd =
create_window(&title, flags, rect.size(), parent as *mut _, initializer).unwrap();
create_window(&title, style, rect.size(), parent as *mut _, initializer).unwrap();

// SAFETY: this handle should be safe to use
let window = unsafe { HWnd::from_raw(hwnd) };
Expand Down
12 changes: 4 additions & 8 deletions src/wrappers/win32.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,18 +1,19 @@
pub mod cursor;
mod dpi;
pub mod h_instance;
mod rect;
mod style;
pub mod uuid;
pub mod window;

pub use dpi::*;
pub use rect::Rect;
pub use style::*;

use std::ptr::null_mut;
use windows_core::{Error, Result, HRESULT};
use windows_sys::Win32::Foundation::{S_FALSE, S_OK};
use windows_sys::Win32::System::Ole::OleInitialize;
use windows_sys::Win32::UI::HiDpi::{
SetProcessDpiAwarenessContext, DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE,
};
use windows_sys::Win32::UI::WindowsAndMessaging::{
DispatchMessageW, GetMessageW, TranslateMessage, MSG,
};
Expand Down Expand Up @@ -51,8 +52,3 @@ pub fn run_thread_message_loop_until(until: impl Fn() -> bool) -> Result<()> {
}
}
}

// Only works on Windows 10 unfortunately.
pub fn set_process_per_monitor_dpi_aware() {
unsafe { SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE) };
}
Loading
Loading