Add scroll-factor Window Rule

niri-config/src/lib.rs

@@ -1079,6 +1079,8 @@ pub struct WindowRule {
     pub variable_refresh_rate: Option<bool>,
     #[knuffel(child)]
     pub default_floating_position: Option<FloatingPosition>,
+    #[knuffel(child, unwrap(argument))]
+    pub scroll_factor: Option<FloatOrInt<0, 100>>,
 }
 
 #[derive(knuffel::Decode, Debug, Default, Clone, PartialEq)]

src/handlers/mod.rs

@@ -343,13 +343,12 @@ impl ClientDndGrabHandler for State {
         // example. On successful drop, additionally activate the target window.
         let mut activate_output = true;
         if let Some(target) = validated.then_some(target).flatten() {
-            if let Some(root) = self.niri.root_surface.get(&target) {
-                if let Some((mapped, _)) = self.niri.layout.find_window_and_output(root) {
-                    let window = mapped.window.clone();
-                    self.niri.layout.activate_window(&window);
-                    self.niri.layer_shell_on_demand_focus = None;
-                    activate_output = false;
-                }
+            let root = self.niri.find_root_shell_surface(&target);
+            if let Some((mapped, _)) = self.niri.layout.find_window_and_output(&root) {
+                let window = mapped.window.clone();
+                self.niri.layout.activate_window(&window);
+                self.niri.layer_shell_on_demand_focus = None;
+                activate_output = false;
             }
         }
 

src/input/mod.rs

@@ -2086,6 +2086,8 @@ impl State {
     }
 
     fn on_pointer_axis<I: InputBackend>(&mut self, event: I::PointerAxisEvent) {
+        let pointer = &self.niri.seat.get_pointer().unwrap();
+
         let source = event.source();
 
         // We received an event for the regular pointer, so show it now. This is also needed for
@@ -2232,12 +2234,20 @@ impl State {
             }
         }
 
+        self.update_pointer_contents();
+
         let scroll_factor = match source {
             AxisSource::Wheel => self.niri.config.borrow().input.mouse.scroll_factor,
             AxisSource::Finger => self.niri.config.borrow().input.touchpad.scroll_factor,
             _ => None,
         };
-        let scroll_factor = scroll_factor.map(|x| x.0).unwrap_or(1.);
+        let window_scroll_factor = pointer
+            .current_focus()
+            .map(|focused| self.niri.find_root_shell_surface(&focused))
+            .and_then(|root| self.niri.layout.find_window_and_output(&root).unzip().0)
+            .and_then(|window| window.rules().scroll_factor);
+        let scroll_factor =
+            scroll_factor.map(|x| x.0).unwrap_or(1.) * window_scroll_factor.unwrap_or(1.);
 
         let horizontal_amount = horizontal_amount.unwrap_or_else(|| {
             // Winit backend, discrete scrolling.
@@ -2278,9 +2288,6 @@ impl State {
             }
         }
 
-        self.update_pointer_contents();
-
-        let pointer = &self.niri.seat.get_pointer().unwrap();
         pointer.axis(self, frame);
         pointer.frame(self);
     }

src/niri.rs

@@ -41,8 +41,8 @@ use smithay::desktop::utils::{
     under_from_surface_tree, update_surface_primary_scanout_output, OutputPresentationFeedback,
 };
 use smithay::desktop::{
-    layer_map_for_output, LayerMap, LayerSurface, PopupGrab, PopupManager, PopupUngrabStrategy,
-    Space, Window, WindowSurfaceType,
+    find_popup_root_surface, layer_map_for_output, LayerMap, LayerSurface, PopupGrab, PopupManager,
+    PopupUngrabStrategy, Space, Window, WindowSurfaceType,
 };
 use smithay::input::keyboard::Layout as KeyboardLayout;
 use smithay::input::pointer::{CursorIcon, CursorImageAttributes, CursorImageStatus, MotionEvent};
@@ -4907,6 +4907,22 @@ impl Niri {
         }
     }
 
+    /// Tries to find and return the root shell surface for a given surface.
+    ///
+    /// I.e. for popups, this function will try to find the parent toplevel or layer surface. For
+    /// regular subsurfaces, it will find the root surface.
+    pub fn find_root_shell_surface(&self, surface: &WlSurface) -> WlSurface {
+        let Some(root) = self.root_surface.get(surface) else {
+            return surface.clone();
+        };
+
+        if let Some(popup) = self.popups.find_popup(root) {
+            return find_popup_root_surface(&popup).unwrap_or_else(|_| root.clone());
+        }
+
+        root.clone()
+    }
+
     #[cfg(feature = "dbus")]
     pub fn on_ipc_outputs_changed(&self) {
         let _span = tracy_client::span!("Niri::on_ipc_outputs_changed");

src/window/mod.rs

@@ -100,6 +100,9 @@ pub struct ResolvedWindowRules {
 
     /// Whether to enable VRR on this window's primary output if it is on-demand.
     pub variable_refresh_rate: Option<bool>,
+
+    /// Multiplier for all scroll events sent to this window.
+    pub scroll_factor: Option<f64>,
 }
 
 impl<'a> WindowRef<'a> {
@@ -190,6 +193,7 @@ impl ResolvedWindowRules {
             clip_to_geometry: None,
             block_out_from: None,
             variable_refresh_rate: None,
+            scroll_factor: None,
         }
     }
 
@@ -301,6 +305,9 @@ impl ResolvedWindowRules {
                 if let Some(x) = rule.variable_refresh_rate {
                     resolved.variable_refresh_rate = Some(x);
                 }
+                if let Some(x) = rule.scroll_factor {
+                    resolved.scroll_factor = Some(x.0);
+                }
             }
 
             resolved.open_on_output = open_on_output.map(|x| x.to_owned());

wiki/Configuration:-Window-Rules.md

@@ -53,6 +53,7 @@ window-rule {
     // block-out-from "screen-capture"
     variable-refresh-rate true
     default-floating-position x=100 y=200 relative-to="bottom-left"
+    scroll-factor 0.75
 
     focus-ring {
         // off
@@ -557,6 +558,23 @@ window-rule {
 }
 ```
 
+#### `scroll-factor`
+
+<sup>Since: next release</sup>
+
+Set a scroll factor for all scroll events sent to a window.
+
+This will be multiplied with the scroll factor set for your input device in the [input](/wiki/Configuration:-Input.md) section.
+
+```kdl
+// Make scrolling in Firefox a bit slower.
+window-rule {
+    match app-id="firefox$"
+
+    scroll-factor 0.75
+}
+```
+
 #### `draw-border-with-background`
 
 Override whether the border and the focus ring draw with a background.