From bbf5f09b21b2f47470c1a660912c5039a52e20d6 Mon Sep 17 00:00:00 2001
From: Varphone Wong <varphone@qq.com>
Date: Thu, 7 Mar 2024 14:08:51 +0800
Subject: [PATCH] `egui`: Add `easing` option to Slider

---
 crates/egui/src/widgets/slider.rs | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/crates/egui/src/widgets/slider.rs b/crates/egui/src/widgets/slider.rs
index 017270fc7..dbb1316b5 100644
--- a/crates/egui/src/widgets/slider.rs
+++ b/crates/egui/src/widgets/slider.rs
@@ -118,6 +118,7 @@ pub struct Slider<'a> {
     trailing_fill: Option<bool>,
     handle_shape: Option<HandleShape>,
     update_while_editing: bool,
+    easing: Option<bool>,
 }
 
 impl<'a> Slider<'a> {
@@ -169,6 +170,7 @@ impl<'a> Slider<'a> {
             trailing_fill: None,
             handle_shape: None,
             update_while_editing: true,
+            easing: None,
         }
     }
 
@@ -399,6 +401,13 @@ impl<'a> Slider<'a> {
         self
     }
 
+    /// Set the easing of the slider.
+    #[inline]
+    pub fn easing(mut self) -> Self {
+        self.easing = Some(true);
+        self
+    }
+
     /// Set custom formatter defining how numbers are converted into text.
     ///
     /// A custom formatter takes a `f64` for the numeric value and a `RangeInclusive<usize>` representing
@@ -636,12 +645,18 @@ impl<'a> Slider<'a> {
     /// For instance, `position` is the mouse position and `position_range` is the physical location of the slider on the screen.
     fn value_from_position(&self, position: f32, position_range: Rangef) -> f64 {
         let normalized = remap_clamp(position, position_range, 0.0..=1.0) as f64;
-        value_from_normalized(normalized, self.range(), &self.spec)
+        let eased_normalized = self.easing.map_or(normalized, |_easing| {
+            emath::easing::quadratic_in(normalized as _) as _
+        });
+        value_from_normalized(eased_normalized, self.range(), &self.spec)
     }
 
     fn position_from_value(&self, value: f64, position_range: Rangef) -> f32 {
         let normalized = normalized_from_value(value, self.range(), &self.spec);
-        lerp(position_range, normalized as f32)
+        let inversed_ease_normalized = self.easing.map_or(normalized, |_easing| {
+            emath::easing::quadratic_in_inverse(normalized as _) as _
+        });
+        lerp(position_range, inversed_ease_normalized as f32)
     }
 
     /// Update the value on each key press when text-editing the value.