Drag very granularly with Shift+Drag

Cargo.lock

@@ -533,6 +533,7 @@ dependencies = [
  "crossbeam",
  "egui",
  "egui-baseview",
+ "lazy_static",
  "nih_plug",
  "parking_lot",
 ]

nih_plug_egui/Cargo.toml

@@ -15,4 +15,5 @@ crossbeam = "0.8"
 egui = "0.16"
 # Upstream doesn't work with the current baseview and egui versions
 egui-baseview = { git = "https://github.com/robbert-vdh/egui-baseview.git", branch = "fix/update-dependencies" }
+lazy_static = "1.4"
 parking_lot = "0.12"

nih_plug_egui/src/widgets/param_slider.rs

@@ -1,13 +1,25 @@
-use egui::{vec2, Response, Sense, Stroke, TextStyle, Ui, Widget};
+use egui::{vec2, Response, Sense, Stroke, TextStyle, Ui, Vec2, Widget};
+use lazy_static::lazy_static;
 
 use super::util;
 use nih_plug::{Param, ParamSetter};
 
+/// When shift+dragging a parameter, one pixel dragged corresponds to this much change in the
+/// noramlized parameter.
+const GRANULAR_DRAG_MULTIPLIER: f32 = 0.0015;
+
+lazy_static! {
+    static ref DRAG_NORMALIZED_START_VALUE_MEMORY_ID: egui::Id = egui::Id::new((file!(), 0));
+    static ref DRAG_AMOUNT_MEMORY_ID: egui::Id = egui::Id::new((file!(), 1));
+}
+
 /// A slider widget similar to [egui::widgets::Slider] that knows about NIH-plug parameters ranges
 /// and can get values for it.
 ///
 /// TODO: Vertical orientation
 /// TODO: Check below for more input methods that should be added
+/// TODO: Decouple the logic from the drawing so we can also do things like nobs without having to
+///       repeat everything
 pub struct ParamSlider<'a, P: Param> {
     param: &'a P,
     setter: &'a ParamSetter<'a>,
@@ -46,9 +58,51 @@ impl<'a, P: Param> ParamSlider<'a, P> {
             .set_parameter_normalized(self.param, normalized_default);
     }
 
+    fn granular_drag(&self, ui: &Ui, drag_delta: Vec2) {
+        // Remember the intial position when we started with the granular drag. This value gets
+        // reset whenever we have a normal itneraction with the slider.
+        let start_value = if Self::get_drag_amount_memory(ui) == 0.0 {
+            Self::set_drag_normalized_start_value_memory(ui, self.normalized_value());
+            self.normalized_value()
+        } else {
+            Self::get_drag_normalized_start_value_memory(ui)
+        };
+
+        let total_drag_distance = drag_delta.x + Self::get_drag_amount_memory(ui);
+        Self::set_drag_amount_memory(ui, total_drag_distance);
+
+        self.set_normalized_value(
+            (start_value + (total_drag_distance * GRANULAR_DRAG_MULTIPLIER)).clamp(0.0, 1.0),
+        );
+    }
+
     fn end_drag(&self) {
         self.setter.end_set_parameter(self.param);
     }
+
+    fn get_drag_normalized_start_value_memory(ui: &Ui) -> f32 {
+        ui.memory()
+            .data
+            .get_temp(*DRAG_NORMALIZED_START_VALUE_MEMORY_ID)
+            .unwrap_or(0.0)
+    }
+
+    fn set_drag_normalized_start_value_memory(ui: &Ui, amount: f32) {
+        ui.memory()
+            .data
+            .insert_temp(*DRAG_NORMALIZED_START_VALUE_MEMORY_ID, amount);
+    }
+
+    fn get_drag_amount_memory(ui: &Ui) -> f32 {
+        ui.memory()
+            .data
+            .get_temp(*DRAG_AMOUNT_MEMORY_ID)
+            .unwrap_or(0.0)
+    }
+
+    fn set_drag_amount_memory(ui: &Ui, amount: f32) {
+        ui.memory().data.insert_temp(*DRAG_AMOUNT_MEMORY_ID, amount);
+    }
 }
 
 impl<P: Param> Widget for ParamSlider<'_, P> {
@@ -82,17 +136,24 @@ impl<P: Param> Widget for ParamSlider<'_, P> {
         // TODO: Optionally add alt+click for value entry?
         // TODO: Handle shift+drag being more granular
         if response.drag_started() {
+            // When beginning a drag or dragging normally, reset the memory used to keep track of
+            // our granular drag
             self.begin_drag();
+            Self::set_drag_amount_memory(ui, 0.0);
         }
         if let Some(click_pos) = response.interact_pointer_pos() {
-            // Like double clicking, Ctrl+Click should reset the parameter
             if ui.input().modifiers.command {
+                // Like double clicking, Ctrl+Click should reset the parameter
                 self.reset_param();
+            } else if ui.input().modifiers.shift {
+                // And shift dragging should switch to a more granulra input method
+                self.granular_drag(ui, response.drag_delta());
             } else {
                 let proportion =
                     egui::emath::remap_clamp(click_pos.x, response.rect.x_range(), 0.0..=1.0)
                         as f64;
                 self.set_normalized_value(proportion as f32);
+                Self::set_drag_amount_memory(ui, 0.0);
             }
         }
         if response.double_clicked() {

plugins/examples/gain-gui/src/lib.rs

@@ -125,6 +125,7 @@ impl Plugin for Gain {
                     // It's not yet fully implemented, as the text is missing.
                     ui.label("Gain (now linked to some random skewed int)");
                     ui.add(widgets::ParamSlider::for_param(&params.some_int, setter));
+                    ui.add(widgets::ParamSlider::for_param(&params.gain, setter));
 
                     // This is a simple naieve version of a parameter slider that's not aware of how
                     // the parmaeters work