Merge pull request #2 from sacha-renault/feat/configurable-sweep-range

Allow customizable sweep range for knob widgets

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 All notable changes to this project will be documented in this file.
 
+## [Unreleased]
+
+### 🚀 Features
+
+- Add configurable sweep range with `with_sweep_range()` method
+
 ## [0.1.9] - 2025-02-04
 
 ### 🚀 Features

examples/example_knob.rs

@@ -117,18 +117,20 @@ impl eframe::App for KnobExample {
                         egui::Color32::from_rgb(100, 255, 100),
                     )
                     .with_size(50.0)
-                    .with_label_format(|v| format!("{:.2}%", v)),
+                    .with_label_format(|v| format!("{:.2}%", v))
+                    .with_sweep_range(1. / 8., 0.75),
                 );
 
                 ui.add(
-                    Knob::new(&mut self.blue_value, 0.0, 100.0, egui_knob::KnobStyle::Dot)
+                    Knob::new(&mut self.blue_value, 0.0, 100., egui_knob::KnobStyle::Dot)
                         .with_label("Top", egui_knob::LabelPosition::Top)
                         .with_colors(
                             egui::Color32::from_rgb(30, 30, 80),
                             egui::Color32::from_rgb(50, 50, 220),
                             egui::Color32::from_rgb(100, 100, 255),
                         )
-                        .with_size(50.0),
+                        .with_size(50.0)
+                        .with_sweep_range(0., 2.),
                 );
             });
         });

src/lib.rs

@@ -1,3 +1,5 @@
+use core::f32;
+
 use egui::{Align2, Color32, Rect, Response, Sense, Stroke, Ui, Vec2, Widget};
 
 /// Position of the label relative to the knob
@@ -42,6 +44,17 @@ pub struct Knob<'a> {
     label_offset: f32,
     label_format: Box<dyn Fn(f32) -> String>,
     step: Option<f32>,
+
+    /// Minimum angle in radians.  
+    /// Specifies the lower bound of the knob's rotation.  
+    /// Expected range: 0.0 to TAU. Values outside this range are allowed if your use case requires it.
+    min_angle: f32,
+
+    /// Maximum angle in radians.  
+    /// Specifies the upper bound of the knob's rotation.
+    /// Can be any value > `min_angle`
+    /// range `max_angle` - `min_angle` > TAU is allowed but will induce multi-turn
+    max_angle: f32,
 }
 
 impl<'a> Knob<'a> {
@@ -69,9 +82,47 @@ impl<'a> Knob<'a> {
             label_offset: 1.0,
             label_format: Box::new(|v| format!("{:.2}", v)),
             step: None,
+
+            // Hardcode those two angles to ENSURE backward compatibility
+            min_angle: -std::f32::consts::PI,
+            max_angle: std::f32::consts::PI * 0.5,
         }
     }
 
+    /// Sets the angular sweep range of the knob
+    ///
+    /// This controls where the knob starts and how far it can rotate. By default,
+    /// knobs start at the left (180°) and sweep 270° clockwise to bottom.
+    ///
+    /// # Arguments
+    /// * `start_angle_normalized` - Starting position as fraction of full circle:
+    ///   - `0.0` = bottom (6 o'clock)
+    ///   - `0.25` = left (9 o'clock)
+    ///   - `0.5` = top (12 o'clock)
+    ///   - `0.75` = right (3 o'clock)
+    /// * `range` - How far the knob can sweep as fraction of full circle:
+    ///   - `0.25` = quarter turn (90°)
+    ///   - `0.5` = half turn (180°)
+    ///   - `0.75` = three-quarter turn (270°)
+    ///   - `1.0` = full turn (360°)
+    ///   - Values > 1.0 create multi-turn knobs
+    ///   - Negative values are clamped to 0.0
+    ///
+    /// Note: the start angle is offset by PI/2 so that `0.0` is at the bottom (6 o'clock)
+    pub fn with_sweep_range(mut self, start_angle_normalized: f32, range: f32) -> Self {
+        if start_angle_normalized.is_nan() || range.is_nan() {
+            // Invalid input, return unchanged
+            return self;
+        }
+
+        self.min_angle =
+            start_angle_normalized.rem_euclid(1.) * f32::consts::TAU + f32::consts::PI / 2.;
+
+        // A range of 1. represent a full turn
+        self.max_angle = self.min_angle + range.max(0.) * f32::consts::TAU;
+        self
+    }
+
     /// Sets the size of the knob
     pub fn with_size(mut self, size: f32) -> Self {
         self.size = size;
@@ -210,8 +261,15 @@ impl Widget for Knob<'_> {
 
         let center = knob_rect.center();
         let radius = knob_size.x / 2.0;
-        let angle = (*self.value - self.min) / (self.max - self.min) * std::f32::consts::PI * 1.5
+        let angle = if self.min == self.max {
-            - std::f32::consts::PI;
+            // If min == max, just return min angle
+            // That's a edge case, using a 0 range knob is pretty useless
+            self.min_angle
+        } else {
+            self.min_angle
+                + (*self.value - self.min) / (self.max - self.min)
+                    * (self.max_angle - self.min_angle)
+        };
 
         painter.circle_stroke(
             center,