Add scroll-factor window rule

Fixes YaLTeR#909.

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

@@ -37,6 +37,7 @@ use self::move_grab::MoveGrab;
 use self::resize_grab::ResizeGrab;
 use self::spatial_movement_grab::SpatialMovementGrab;
 use crate::layout::scrolling::ScrollDirection;
+use crate::layout::LayoutElement;
 use crate::niri::State;
 use crate::ui::screenshot_ui::ScreenshotUi;
 use crate::utils::spawning::spawn;
@@ -2171,7 +2172,12 @@ impl State {
             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 = self
+            .niri
+            .window_under_cursor()
+            .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.

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());