Add Options::line_scroll_speed and scroll_zoom_speed (#4532)

This lets integrations and user change how sensitive egui is to scroll
events

crates/egui/src/context.rs

@@ -442,6 +442,7 @@ impl ContextImpl {
             new_raw_input,
             viewport.repaint.requested_immediate_repaint_prev_frame(),
             pixels_per_point,
+            &self.memory.options,
         );
 
         let screen_rect = viewport.input.screen_rect;

crates/egui/src/input_state.rs

@@ -183,6 +183,7 @@ impl InputState {
         mut new: RawInput,
         requested_immediate_repaint_prev_frame: bool,
         pixels_per_point: f32,
+        options: &crate::Options,
     ) -> Self {
         crate::profile_function!();
 
@@ -235,17 +236,7 @@ impl InputState {
                 } => {
                     let mut delta = match unit {
                         MouseWheelUnit::Point => *delta,
-                        MouseWheelUnit::Line => {
-                            // TODO(emilk): figure out why these constants need to be different on web and on native (winit).
-                            let is_web = cfg!(target_arch = "wasm32");
-                            let points_per_scroll_line = if is_web {
-                                8.0
-                            } else {
-                                50.0 // Scroll speed decided by consensus: https://github.com/emilk/egui/issues/461
-                            };
-
-                            points_per_scroll_line * *delta
-                        }
+                        MouseWheelUnit::Line => options.line_scroll_speed * *delta,
                         MouseWheelUnit::Page => screen_rect.height() * *delta,
                     };
 
@@ -319,7 +310,8 @@ impl InputState {
                     unprocessed_scroll_delta_for_zoom -= applied;
                 }
 
-                zoom_factor_delta *= (smooth_scroll_delta_for_zoom / 200.0).exp();
+                zoom_factor_delta *=
+                    (options.scroll_zoom_speed * smooth_scroll_delta_for_zoom).exp();
             }
         }
 

crates/egui/src/memory.rs

@@ -227,10 +227,26 @@ pub struct Options {
     ///
     /// By default this is `true` in debug builds.
     pub warn_on_id_clash: bool,
+
+    // ------------------------------
+    // Input:
+    /// Multiplier for the scroll speed when reported in [`crate::MouseWheelUnit::Line`]s.
+    pub line_scroll_speed: f32,
+
+    /// Controls the speed at which we zoom in when doing ctrl/cmd + scroll.
+    pub scroll_zoom_speed: f32,
 }
 
 impl Default for Options {
     fn default() -> Self {
+        // TODO(emilk): figure out why these constants need to be different on web and on native (winit).
+        let is_web = cfg!(target_arch = "wasm32");
+        let line_scroll_speed = if is_web {
+            8.0
+        } else {
+            40.0 // Scroll speed decided by consensus: https://github.com/emilk/egui/issues/461
+        };
+
         Self {
             style: Default::default(),
             zoom_factor: 1.0,
@@ -240,6 +256,10 @@ impl Default for Options {
             screen_reader: false,
             preload_font_glyphs: true,
             warn_on_id_clash: cfg!(debug_assertions),
+
+            // Input:
+            line_scroll_speed,
+            scroll_zoom_speed: 1.0 / 200.0,
         }
     }
 }
@@ -256,6 +276,9 @@ impl Options {
             screen_reader: _, // needs to come from the integration
             preload_font_glyphs: _,
             warn_on_id_clash,
+
+            line_scroll_speed,
+            scroll_zoom_speed,
         } = self;
 
         use crate::Widget as _;
@@ -292,6 +315,27 @@ impl Options {
                 });
             });
 
+        CollapsingHeader::new("🖱 Input")
+            .default_open(false)
+            .show(ui, |ui| {
+                ui.horizontal(|ui| {
+                    ui.label("Line scroll speed");
+                    ui.add(
+                        crate::DragValue::new(line_scroll_speed).clamp_range(0.0..=f32::INFINITY),
+                    )
+                    .on_hover_text("How many lines to scroll with each tick of the mouse wheel");
+                });
+                ui.horizontal(|ui| {
+                    ui.label("Scroll zoom speed");
+                    ui.add(
+                        crate::DragValue::new(scroll_zoom_speed)
+                            .clamp_range(0.0..=f32::INFINITY)
+                            .speed(0.001),
+                    )
+                    .on_hover_text("How fast to zoom with ctrl/cmd + scroll");
+                });
+            });
+
         ui.vertical_centered(|ui| crate::reset_button(ui, self, "Reset all"));
     }
 }