Use fractional scaling when setting scale through xsettings

Fixes #168

src/server/dispatch.rs

@@ -1350,11 +1350,11 @@ impl<C: XConnection> GlobalDispatch<WlOutput, Global> for ServerState<C> {
             (
                 server,
                 client,
-                event::OutputScaleFactor(1),
+                event::OutputScaleFactor::Output(1),
                 event::OutputDimensions::default(),
             ),
         );
-        state.output_scales_updated = true;
+        state.updated_outputs.push(entity);
     }
 }
 global_dispatch_with_events!(WlDrmServer, WlDrmClient);

src/server/event.rs

@@ -44,12 +44,15 @@ use wayland_server::protocol::{
     wl_seat::WlSeat, wl_touch::WlTouch,
 };
 
+#[derive(Copy, Clone)]
+pub(super) struct SurfaceScaleFactor(pub f64);
+
 #[derive(hecs::Bundle)]
 pub(super) struct SurfaceBundle {
     pub client: client::wl_surface::WlSurface,
     pub server: WlSurface,
-    pub scale: SurfaceScaleFactor,
     pub viewport: WpViewport,
+    pub scale: SurfaceScaleFactor,
 }
 
 #[derive(Debug)]
@@ -86,12 +89,22 @@ impl Event for SurfaceEvents {
                 wp_fractional_scale_v1::Event::PreferredScale { scale } => {
                     let entity = state.world.entity(target).unwrap();
                     let factor = scale as f64 / 120.0;
-                    entity.get::<&mut SurfaceScaleFactor>().unwrap().0 = factor;
-                    log::debug!(
+                    debug!(
                         "{} scale factor: {}",
                         entity.get::<&WlSurface>().unwrap().id(),
                         factor
                     );
+
+                    entity.get::<&mut SurfaceScaleFactor>().unwrap().0 = factor;
+
+                    if let Some(OnOutput(output)) = entity.get::<&OnOutput>().as_deref().copied() {
+                        if update_output_scale(
+                            state.world.query_one(output).unwrap(),
+                            OutputScaleFactor::Fractional(factor),
+                        ) {
+                            state.updated_outputs.push(output);
+                        }
+                    }
                     if entity.has::<WindowData>() {
                         update_surface_viewport(state.world.query_one(target).unwrap());
                     }
@@ -126,11 +139,6 @@ impl SurfaceEvents {
                 surface.enter(&output);
                 let on_output = OnOutput(output_entity);
 
-                if state.fractional_scale.is_none() {
-                    data.get::<&mut SurfaceScaleFactor>().unwrap().0 =
-                        output_data.get::<&OutputScaleFactor>().unwrap().0 as f64;
-                }
-
                 debug!("{} entered {}", surface.id(), output.id());
 
                 let mut query = data.query::<(&x::Window, &mut WindowData)>();
@@ -151,9 +159,19 @@ impl SurfaceEvents {
                         conn.focus_window(*window, output);
                     }
 
-                    drop(query);
                     if state.fractional_scale.is_none() {
+                        let output_scale = output_data.get::<&OutputScaleFactor>().unwrap().get();
+                        data.get::<&mut SurfaceScaleFactor>().unwrap().0 = output_scale;
+                        drop(query);
                         update_surface_viewport(state.world.query_one(target).unwrap());
+                    } else {
+                        let scale = data.get::<&SurfaceScaleFactor>().unwrap();
+                        if update_output_scale(
+                            state.world.query_one(on_output.0).unwrap(),
+                            OutputScaleFactor::Fractional(scale.0),
+                        ) {
+                            state.updated_outputs.push(on_output.0);
+                        }
                     }
                 }
                 cmd.insert_one(target, on_output);
@@ -200,20 +218,19 @@ impl SurfaceEvents {
         drop(xdg);
 
         if let Some(pending) = pending {
-            let mut query = data.query::<(&mut SurfaceScaleFactor, &x::Window, &mut WindowData)>();
+            let mut query = data.query::<(&SurfaceScaleFactor, &x::Window, &mut WindowData)>();
             let (scale_factor, window, window_data) = query.get().unwrap();
-            let scale_factor = scale_factor.0;
 
             let window = *window;
-            let x = (pending.x as f64 * scale_factor) as i32 + window_data.output_offset.x;
-            let y = (pending.y as f64 * scale_factor) as i32 + window_data.output_offset.y;
+            let x = (pending.x as f64 * scale_factor.0) as i32 + window_data.output_offset.x;
+            let y = (pending.y as f64 * scale_factor.0) as i32 + window_data.output_offset.y;
             let width = if pending.width > 0 {
-                (pending.width as f64 * scale_factor) as u16
+                (pending.width as f64 * scale_factor.0) as u16
             } else {
                 window_data.attrs.dims.width
             };
             let height = if pending.height > 0 {
-                (pending.height as f64 * scale_factor) as u16
+                (pending.height as f64 * scale_factor.0) as u16
             } else {
                 window_data.attrs.dims.height
             };
@@ -452,7 +469,7 @@ impl Event for client::wl_pointer::Event {
 
                 let surface_is_popup = matches!(role, SurfaceRole::Popup(_));
                 let mut do_enter = || {
-                    debug!("pointer entering {} ({serial})", surface.id());
+                    debug!("pointer entering {} ({serial} {})", surface.id(), scale.0);
                     server.enter(serial, surface, surface_x * scale.0, surface_y * scale.0);
                     state.connection.as_mut().unwrap().raise_to_top(*window);
                     if !surface_is_popup {
@@ -488,6 +505,7 @@ impl Event for client::wl_pointer::Event {
                 cmd.run_on(&mut state.world);
             }
             client::wl_pointer::Event::Leave { serial, surface } => {
+                let _ = state.world.remove_one::<PendingEnter>(target);
                 if !surface.is_alive() {
                     return;
                 }
@@ -720,13 +738,47 @@ impl Event for client::wl_touch::Event {
     }
 }
 
+#[derive(Copy, Clone)]
 pub(super) struct OnOutput(pub Entity);
 struct OutputName(String);
 fn get_output_name(output: Option<&OnOutput>, world: &World) -> Option<String> {
     output.map(|o| world.get::<&OutputName>(o.0).unwrap().0.clone())
 }
 
-pub(super) struct OutputScaleFactor(pub i32);
+#[derive(Copy, Clone, PartialEq, Debug)]
+pub(super) enum OutputScaleFactor {
+    Output(i32),
+    Fractional(f64),
+}
+
+impl OutputScaleFactor {
+    pub(super) fn get(&self) -> f64 {
+        match *self {
+            Self::Output(o) => o as _,
+            Self::Fractional(f) => f,
+        }
+    }
+}
+
+#[must_use]
+fn update_output_scale(
+    mut output_scale: hecs::QueryOne<&mut OutputScaleFactor>,
+    factor: OutputScaleFactor,
+) -> bool {
+    let output_scale = output_scale.get().unwrap();
+    if matches!(output_scale, OutputScaleFactor::Fractional(..))
+        && matches!(factor, OutputScaleFactor::Output(..))
+    {
+        return false;
+    }
+
+    if *output_scale != factor {
+        *output_scale = factor;
+        return true;
+    }
+
+    false
+}
 
 enum OutputDimensionsSource {
     // The data in this variant is the values needed for the wl_output.geometry event.
@@ -1012,26 +1064,15 @@ impl OutputEvent {
                     "{} scale: {factor}",
                     state.world.get::<&WlOutput>(target).unwrap().id()
                 );
-                state.world.get::<&mut OutputScaleFactor>(target).unwrap().0 = factor;
+                if update_output_scale(
+                    state.world.query_one(target).unwrap(),
+                    OutputScaleFactor::Output(factor),
+                ) {
+                    state.updated_outputs.push(target);
+                }
                 if state.fractional_scale.is_none() {
-                    let mut surfaces = vec![];
-                    for (entity, (scale, _)) in state
-                        .world
-                        .query_mut::<(&mut SurfaceScaleFactor, &OnOutput)>()
-                        .with::<&WindowData>()
-                        .into_iter()
-                        .filter(|(_, (_, o))| o.0 == target)
-                    {
-                        surfaces.push(entity);
-                        scale.0 = factor as f64;
-                    }
-                    for entity in surfaces {
-                        update_surface_viewport(state.world.query_one(entity).unwrap());
-                    }
-
                     state.world.get::<&WlOutput>(target).unwrap().scale(factor);
                 }
-                state.output_scales_updated = true;
             }
             Event::Name { name } => {
                 state

src/server/mod.rs

@@ -173,9 +173,6 @@ struct SurfaceAttach {
 #[derive(PartialEq, Eq)]
 struct SurfaceSerial([u32; 2]);
 
-#[derive(Copy, Clone)]
-struct SurfaceScaleFactor(f64);
-
 #[derive(Debug)]
 enum SurfaceRole {
     Toplevel(Option<ToplevelData>),
@@ -418,8 +415,8 @@ pub struct ServerState<C: XConnection> {
     activation_state: Option<ActivationState>,
     global_output_offset: GlobalOutputOffset,
     global_offset_updated: bool,
-    output_scales_updated: bool,
-    new_scale: Option<i32>,
+    updated_outputs: Vec<Entity>,
+    new_scale: Option<f64>,
 }
 
 impl<C: XConnection> ServerState<C> {
@@ -507,7 +504,7 @@ impl<C: XConnection> ServerState<C> {
                 },
             },
             global_offset_updated: false,
-            output_scales_updated: false,
+            updated_outputs: Vec::new(),
             new_scale: None,
             decoration_manager,
             world: MyWorld::new(global_list),
@@ -999,19 +996,42 @@ impl<C: XConnection> ServerState<C> {
             self.global_offset_updated = false;
         }
 
-        if self.output_scales_updated {
+        if !self.updated_outputs.is_empty() {
+            for output in self.updated_outputs.drain(..) {
+                let output_scale = self.world.get::<&OutputScaleFactor>(output).unwrap();
+                if matches!(*output_scale, OutputScaleFactor::Output(..)) {
+                    let mut surface_query = self
+                        .world
+                        .query::<(&OnOutput, &mut SurfaceScaleFactor)>()
+                        .with::<(&WindowData, &WlSurface)>();
+
+                    let mut surfaces = vec![];
+                    for (surface, (OnOutput(s_output), surface_scale)) in surface_query.iter() {
+                        if *s_output == output {
+                            surface_scale.0 = output_scale.get();
+                            surfaces.push(surface);
+                        }
+                    }
+
+                    drop(surface_query);
+                    for surface in surfaces {
+                        update_surface_viewport(self.world.query_one(surface).unwrap());
+                    }
+                }
+            }
+
             let mut mixed_scale = false;
             let mut scale;
 
             let mut outputs = self.world.query_mut::<&OutputScaleFactor>().into_iter();
             let (_, output_scale) = outputs.next().unwrap();
 
-            scale = output_scale.0;
+            scale = output_scale.get();
 
             for (_, output_scale) in outputs {
-                if output_scale.0 != scale {
+                if output_scale.get() != scale {
                     mixed_scale = true;
-                    scale = scale.min(output_scale.0);
+                    scale = scale.min(output_scale.get());
                 }
             }
 
@@ -1021,8 +1041,6 @@ impl<C: XConnection> ServerState<C> {
 
             debug!("Using new scale {scale}");
             self.new_scale = Some(scale);
-
-            self.output_scales_updated = false;
         }
 
         {
@@ -1049,7 +1067,7 @@ impl<C: XConnection> ServerState<C> {
             .expect("Failed flushing clientside events");
     }
 
-    pub fn new_global_scale(&mut self) -> Option<i32> {
+    pub fn new_global_scale(&mut self) -> Option<f64> {
         self.new_scale.take()
     }
 
@@ -1156,26 +1174,18 @@ impl<C: XConnection> ServerState<C> {
             }
         }
 
-        let initial_scale;
         let role = if let Some(parent) = popup_for {
-            let data;
-            (initial_scale, data) = self.create_popup(entity, xdg_surface, parent);
+            let data = self.create_popup(entity, xdg_surface, parent);
             SurfaceRole::Popup(Some(data))
         } else {
-            initial_scale = 1.0;
             let data = self.create_toplevel(entity, xdg_surface, fullscreen);
             SurfaceRole::Toplevel(Some(data))
         };
 
-        let (surface_role, scale_factor, client) = self
+        let (surface_role, client) = self
             .world
-            .query_one_mut::<(
-                Option<&SurfaceRole>,
-                &mut SurfaceScaleFactor,
-                &client::wl_surface::WlSurface,
-            )>(entity)
+            .query_one_mut::<(Option<&SurfaceRole>, &client::wl_surface::WlSurface)>(entity)
             .unwrap();
-        scale_factor.0 = initial_scale;
 
         let new_role_type = std::mem::discriminant(&role);
         if let Some(role) = surface_role {
@@ -1294,13 +1304,13 @@ impl<C: XConnection> ServerState<C> {
         }
     }
 
-    fn create_popup(
-        &mut self,
-        entity: Entity,
-        xdg: XdgSurface,
-        parent: x::Window,
-    ) -> (f64, PopupData) {
-        let window = self.world.get::<&WindowData>(entity).unwrap();
+    fn create_popup(&mut self, entity: Entity, xdg: XdgSurface, parent: x::Window) -> PopupData {
+        let mut query = self
+            .world
+            .query_one::<(&WindowData, &mut SurfaceScaleFactor)>(entity)
+            .unwrap();
+
+        let (window, scale) = query.get().unwrap();
         let mut parent_query = self
             .world
             .query_one::<(&WindowData, &SurfaceScaleFactor, &SurfaceRole)>(self.windows[&parent])
@@ -1308,6 +1318,7 @@ impl<C: XConnection> ServerState<C> {
         let (parent_window, parent_scale, parent_role) = parent_query.get().unwrap();
         let parent_dims = parent_window.attrs.dims;
         let initial_scale = parent_scale.0;
+        *scale = *parent_scale;
 
         debug!(
             "creating popup ({:?}) {:?} {:?} {:?} {entity:?} (scale: {initial_scale})",
@@ -1340,8 +1351,6 @@ impl<C: XConnection> ServerState<C> {
             entity,
         );
 
-        (
-            initial_scale,
         PopupData {
             popup,
             positioner,
@@ -1350,8 +1359,7 @@ impl<C: XConnection> ServerState<C> {
                 configured: false,
                 pending: None,
             },
-            },
-        )
+        }
     }
 
     fn close_x_window(&mut self, window: x::Window) {

src/server/tests.rs

@@ -1965,6 +1965,7 @@ fn fractional_scale_popup() {
         testwl.enable_fractional_scale();
     });
     let comp = f.compositor();
+    let (_, output) = f.new_output(0, 0);
 
     let toplevel = unsafe { Window::new(1) };
     let (_, toplevel_id) = f.create_toplevel(&comp, toplevel);
@@ -1978,6 +1979,7 @@ fn fractional_scale_popup() {
         .expect("No fractional scale for surface");
 
     fractional.preferred_scale(180); // 1.5 scale
+    f.testwl.move_surface_to_output(toplevel_id, &output);
     f.run();
     f.run();
 
@@ -2038,6 +2040,7 @@ fn fractional_scale_small_popup() {
     });
     let comp = f.compositor();
 
+    let (_, output) = f.new_output(0, 0);
     let toplevel = unsafe { Window::new(1) };
     let (_, toplevel_id) = f.create_toplevel(&comp, toplevel);
     let data = f.testwl.get_surface_data(toplevel_id).unwrap();
@@ -2046,6 +2049,7 @@ fn fractional_scale_small_popup() {
         .as_ref()
         .expect("Missing fracitonal scale data");
     fractional.preferred_scale(180); // 1.5 scale
+    f.testwl.move_surface_to_output(toplevel_id, &output);
     f.run();
     f.run();
 

src/xstate/settings.rs

@@ -27,7 +27,7 @@ impl XState {
         }
     }
 
-    pub(crate) fn update_global_scale(&mut self, scale: i32) {
+    pub(crate) fn update_global_scale(&mut self, scale: f64) {
         self.settings.set_scale(scale);
         self.connection
             .send_and_check_request(&x::ChangeProperty {
@@ -57,6 +57,7 @@ pub(super) struct Settings {
     settings: HashMap<&'static str, IntSetting>,
 }
 
+#[derive(Copy, Clone)]
 struct IntSetting {
     value: i32,
     last_change_serial: u32,
@@ -160,17 +161,26 @@ impl Settings {
         data
     }
 
-    fn set_scale(&mut self, scale: i32) {
+    fn set_scale(&mut self, scale: f64) {
         self.serial += 1;
 
-        self.settings.entry(XFT_DPI).insert_entry(IntSetting {
-            value: scale * DEFAULT_DPI * DPI_SCALE_FACTOR,
+        let setting = IntSetting {
+            value: (scale * DEFAULT_DPI as f64 * DPI_SCALE_FACTOR as f64).round() as i32,
+            last_change_serial: self.serial,
+        };
+        self.settings.entry(XFT_DPI).insert_entry(setting);
+        // Gdk/WindowScalingFactor + Gdk/UnscaledDPI is identical to setting
+        // GDK_SCALE = scale and then GDK_DPI_SCALE = 1 / scale.
+        self.settings
+            .entry(GDK_UNSCALED_DPI)
+            .insert_entry(IntSetting {
+                value: setting.value / scale as i32,
                 last_change_serial: self.serial,
             });
         self.settings
             .entry(GDK_WINDOW_SCALE)
             .insert_entry(IntSetting {
-                value: scale,
+                value: scale as i32,
                 last_change_serial: self.serial,
             });
     }

tests/integration.rs

@@ -329,6 +329,15 @@ xcb::atoms_struct! {
     }
 }
 
+struct Settings {
+    serial: u32,
+    data: HashMap<String, Setting>,
+}
+struct Setting {
+    value: i32,
+    last_change: u32,
+}
+
 struct Connection {
     inner: xcb::Connection,
     pollfd: PollFd<'static>,
@@ -564,6 +573,56 @@ impl Connection {
         })
         .unwrap();
     }
+
+    fn get_xsettings(&self) -> Settings {
+        let owner = self
+            .get_reply(&x::GetSelectionOwner {
+                selection: self.atoms.xsettings,
+            })
+            .owner();
+
+        let reply = self.get_reply(&x::GetProperty {
+            delete: false,
+            window: owner,
+            property: self.atoms.xsettings_setting,
+            r#type: self.atoms.xsettings_setting,
+            long_offset: 0,
+            long_length: 60,
+        });
+        assert_eq!(reply.r#type(), self.atoms.xsettings_setting);
+
+        let data = reply.value::<u8>();
+
+        let byte_order = data[0];
+        assert_eq!(byte_order, 0);
+        let serial = u32::from_le_bytes(data[4..8].try_into().unwrap());
+        let num_settings = u32::from_le_bytes(data[8..12].try_into().unwrap());
+
+        let mut current_idx = 12;
+        let mut settings = HashMap::new();
+        for _ in 0..num_settings {
+            assert_eq!(&data[current_idx..current_idx + 2], &[0, 0]);
+            let name_len =
+                u16::from_le_bytes(data[current_idx + 2..current_idx + 4].try_into().unwrap());
+
+            let padding_start = current_idx + 4 + name_len as usize;
+            let name = String::from_utf8(data[current_idx + 4..padding_start].to_vec()).unwrap();
+            let num_padding_bytes = (4 - (name_len as usize % 4)) % 4;
+            let data_start = padding_start + num_padding_bytes;
+            let last_change =
+                u32::from_le_bytes(data[data_start..data_start + 4].try_into().unwrap());
+            let value =
+                i32::from_le_bytes(data[data_start + 4..data_start + 8].try_into().unwrap());
+
+            settings.insert(name, Setting { value, last_change });
+            current_idx = data_start + 8;
+        }
+
+        Settings {
+            serial,
+            data: settings,
+        }
+    }
 }
 
 #[test]
@@ -1627,6 +1686,8 @@ fn forced_1x_scale_consistent_x11_size() {
     // Update scale
     output.scale(3);
     output.done();
+    f.wait_and_dispatch();
+
     f.testwl
         .configure_toplevel(surface, 100, 100, vec![xdg_toplevel::State::Activated]);
     f.testwl.focus_toplevel(surface);
@@ -1736,66 +1797,7 @@ fn xsettings_scale() {
     let connection = Connection::new(&f.display);
     f.testwl.enable_xdg_output_manager();
 
-    struct Settings {
-        serial: u32,
-        data: HashMap<String, Setting>,
-    }
-    struct Setting {
-        value: i32,
-        last_change: u32,
-    }
-
-    let owner = connection
-        .get_reply(&x::GetSelectionOwner {
-            selection: connection.atoms.xsettings,
-        })
-        .owner();
-
-    let get_settings = || -> Settings {
-        let reply = connection.get_reply(&x::GetProperty {
-            delete: false,
-            window: owner,
-            property: connection.atoms.xsettings_setting,
-            r#type: connection.atoms.xsettings_setting,
-            long_offset: 0,
-            long_length: 60,
-        });
-        assert_eq!(reply.r#type(), connection.atoms.xsettings_setting);
-
-        let data = reply.value::<u8>();
-
-        let byte_order = data[0];
-        assert_eq!(byte_order, 0);
-        let serial = u32::from_le_bytes(data[4..8].try_into().unwrap());
-        let num_settings = u32::from_le_bytes(data[8..12].try_into().unwrap());
-
-        let mut current_idx = 12;
-        let mut settings = HashMap::new();
-        for _ in 0..num_settings {
-            assert_eq!(&data[current_idx..current_idx + 2], &[0, 0]);
-            let name_len =
-                u16::from_le_bytes(data[current_idx + 2..current_idx + 4].try_into().unwrap());
-
-            let padding_start = current_idx + 4 + name_len as usize;
-            let name = String::from_utf8(data[current_idx + 4..padding_start].to_vec()).unwrap();
-            let num_padding_bytes = (4 - (name_len as usize % 4)) % 4;
-            let data_start = padding_start + num_padding_bytes;
-            let last_change =
-                u32::from_le_bytes(data[data_start..data_start + 4].try_into().unwrap());
-            let value =
-                i32::from_le_bytes(data[data_start + 4..data_start + 8].try_into().unwrap());
-
-            settings.insert(name, Setting { value, last_change });
-            current_idx = data_start + 8;
-        }
-
-        Settings {
-            serial,
-            data: settings,
-        }
-    };
-
-    let settings = get_settings();
+    let settings = connection.get_xsettings();
     let settings_serial = settings.serial;
     assert_eq!(settings.data["Xft/DPI"].value, 96 * 1024);
     let dpi_serial = settings.data["Xft/DPI"].last_change;
@@ -1809,20 +1811,17 @@ fn xsettings_scale() {
     output.done();
     f.wait_and_dispatch();
 
-    let settings = get_settings();
+    let settings = connection.get_xsettings();
     assert!(settings.serial > settings_serial);
     assert_eq!(settings.data["Xft/DPI"].value, 2 * 96 * 1024);
     assert!(settings.data["Xft/DPI"].last_change > dpi_serial);
     assert_eq!(settings.data["Gdk/WindowScalingFactor"].value, 2);
     assert!(settings.data["Gdk/WindowScalingFactor"].last_change > window_serial);
     assert_eq!(settings.data["Gdk/UnscaledDPI"].value, 96 * 1024);
-    assert_eq!(
-        settings.data["Gdk/UnscaledDPI"].last_change,
-        unscaled_serial
-    );
+    assert!(settings.data["Gdk/UnscaledDPI"].last_change > unscaled_serial);
 
     let output2 = f.create_output(0, 0);
-    let settings = get_settings();
+    let settings = connection.get_xsettings();
     assert_eq!(settings.data["Xft/DPI"].value, 96 * 1024);
     assert_eq!(settings.data["Gdk/WindowScalingFactor"].value, 1);
     assert_eq!(settings.data["Gdk/UnscaledDPI"].value, 96 * 1024);
@@ -1832,12 +1831,68 @@ fn xsettings_scale() {
     f.testwl.dispatch();
     std::thread::sleep(Duration::from_millis(1));
 
-    let settings = get_settings();
+    let settings = connection.get_xsettings();
     assert_eq!(settings.data["Xft/DPI"].value, 2 * 96 * 1024);
     assert_eq!(settings.data["Gdk/WindowScalingFactor"].value, 2);
     assert_eq!(settings.data["Gdk/UnscaledDPI"].value, 96 * 1024);
 }
 
+#[test]
+fn xsettings_fractional_scale() {
+    let mut f = Fixture::new_preset(|testwl| {
+        testwl.new_output(0, 0); // WL-1
+        testwl.enable_fractional_scale();
+    });
+    let mut connection = Connection::new(&f.display);
+    f.testwl.enable_xdg_output_manager();
+
+    let output = f.testwl.last_created_output();
+
+    let window = connection.new_window(connection.root, 0, 0, 20, 20, false);
+    let surface = f.map_as_toplevel(&mut connection, window);
+
+    let data = f
+        .testwl
+        .get_surface_data(surface)
+        .expect("Missing surface data");
+    let fractional = data
+        .fractional
+        .as_ref()
+        .expect("No fractional scale for surface");
+
+    fractional.preferred_scale(180); // 1.5 scale
+    f.testwl.move_surface_to_output(surface, &output);
+
+    f.wait_and_dispatch();
+    let settings = connection.get_xsettings();
+
+    assert_eq!(
+        settings.data["Xft/DPI"].value,
+        (1.5 * 96_f64 * 1024_f64).round() as i32
+    );
+    assert_eq!(settings.data["Gdk/WindowScalingFactor"].value, 1);
+    assert_eq!(
+        settings.data["Gdk/UnscaledDPI"].value,
+        (1.5 * 96_f64 * 1024_f64).round() as i32
+    );
+
+    let data = f.testwl.get_surface_data(surface).unwrap();
+    let fractional = data.fractional.as_ref().unwrap();
+    fractional.preferred_scale(300); // 2.5 scale
+    f.wait_and_dispatch();
+
+    let settings = connection.get_xsettings();
+    assert_eq!(
+        settings.data["Xft/DPI"].value,
+        (2.5 * 96_f64 * 1024_f64).round() as i32
+    );
+    assert_eq!(settings.data["Gdk/WindowScalingFactor"].value, 2);
+    assert_eq!(
+        settings.data["Gdk/UnscaledDPI"].value,
+        (2.5 / 2.0 * 96_f64 * 1024_f64).round() as i32
+    );
+}
+
 #[test]
 fn xsettings_switch_owner() {
     let f = Fixture::new();