From d97826e6a3afa2c3524af980cab4abee88c39fa5 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Tue, 22 Mar 2022 23:28:15 +0100
Subject: [PATCH] Apply even ParamSlider Step distribution to input

This remaps the input range to be the same as the displayed values since
the actual normalized number range has the numbers at the edge of the
range taking up half as much of the range as the other numbers.
---
 nih_plug_vizia/src/widgets/param_slider.rs | 38 ++++++++++++++++++----
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/nih_plug_vizia/src/widgets/param_slider.rs b/nih_plug_vizia/src/widgets/param_slider.rs
index 3cf18ff7..caab720d 100644
--- a/nih_plug_vizia/src/widgets/param_slider.rs
+++ b/nih_plug_vizia/src/widgets/param_slider.rs
@@ -216,9 +216,8 @@ impl ParamSlider {
                                                 // across the range.
                                                 let step_count = step_count.unwrap() as f32;
                                                 let discrete_values = step_count + 1.0;
-                                                let previous_step = (current_value * step_count)
-                                                    .floor()
-                                                    / discrete_values;
+                                                let previous_step =
+                                                    (current_value * step_count) / discrete_values;
                                                 (previous_step, discrete_values.recip())
                                             }
                                             ParamSliderStyle::CurrentStep { .. }
@@ -317,6 +316,33 @@ impl ParamSlider {
             ));
         }
     }
+
+    /// `set_normalized_value()`, but resulting from a mouse drag. When using the 'even' stepped
+    /// slider styles from [`ParamSliderStyle`] this will remap the normalized range to match up
+    /// with the fill value display.
+    fn set_normalized_value_drag(&self, cx: &mut Context, normalized_value: f32) {
+        let normalized_value = match (cx.data(), unsafe { self.param_ptr.step_count() }) {
+            (
+                Some(ParamSliderInternal {
+                    style:
+                        ParamSliderStyle::CurrentStep { even: true }
+                        | ParamSliderStyle::CurrentStepLabeled { even: true },
+                    ..
+                }),
+                Some(step_count),
+            ) => {
+                // We'll remap the value range to be the same as the displayed range, e.g. with each
+                // value occupying an equal area on the slider instead of the centers of those
+                // ranges being distributed over the entire `[0, 1]` range.
+                let discrete_values = step_count as f32 + 1.0;
+                let rounded_value = ((normalized_value * discrete_values) - 0.5).round();
+                rounded_value / step_count as f32
+            }
+            _ => normalized_value,
+        };
+
+        self.set_normalized_value(cx, normalized_value);
+    }
 }
 
 impl View for ParamSlider {
@@ -377,7 +403,7 @@ impl View for ParamSlider {
                             }));
                         } else {
                             self.granular_drag_start_x_value = None;
-                            self.set_normalized_value(
+                            self.set_normalized_value_drag(
                                 cx,
                                 util::remap_current_entity_x_coordinate(cx, cx.mouse.cursorx),
                             );
@@ -414,7 +440,7 @@ impl View for ParamSlider {
                                     })
                                 });
 
-                            self.set_normalized_value(
+                            self.set_normalized_value_drag(
                                 cx,
                                 util::remap_current_entity_x_coordinate(
                                     cx,
@@ -426,7 +452,7 @@ impl View for ParamSlider {
                         } else {
                             self.granular_drag_start_x_value = None;
 
-                            self.set_normalized_value(
+                            self.set_normalized_value_drag(
                                 cx,
                                 util::remap_current_entity_x_coordinate(cx, *x),
                             );