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/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/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.