Add symmetrically and asymmetrically skewed ranges

This is super useful. I'm sure the symmetrical implementation can be
optimized a lot, but my math-fu was not strong enough today.

src/param/range.rs

@@ -16,11 +16,31 @@
 
 //! Different ranges for numeric parameters.
 
-/// A distribution for a parameter's range. Probably need to add some forms of skewed ranges and
-/// maybe a callback based implementation at some point.
+/// A distribution for a parameter's range. All range endpoints are inclusive.
 #[derive(Debug)]
 pub enum Range<T> {
+    /// The values are uniformly distributed between `min` and `max`.
     Linear { min: T, max: T },
+    /// The range is skewed by a factor. Values above 1.0 will make the end of the range wider,
+    /// while values between 0 and 1 will skew the range towards the start. Use [Range::skew_factor]
+    /// for a more intuitively way to calculate the skew factor where positive values skew the range
+    /// towards the end while negative values skew the range toward the start.
+    Skewed { min: T, max: T, factor: f32 },
+    /// The same as [Range::Skewed], but with the skewing happening from a central point.
+    SymmetricalSkewed {
+        min: T,
+        max: T,
+        factor: f32,
+        center: T,
+    },
+}
+
+impl Range<()> {
+    /// Calculate a skew factor for [Range::Skewed] and [Range::SymmetricalSkewed]. Positive values
+    /// make the end of the range wider while negative make the start of the range wider.
+    pub fn skew_factor(factor: f32) -> f32 {
+        2.0f32.powf(factor)
+    }
 }
 
 /// A normalizable range for type `T`, where `self` is expected to be a type `R<T>`. Higher kinded
@@ -51,6 +71,34 @@ impl NormalizebleRange<f32> for Range<f32> {
     fn normalize(&self, plain: f32) -> f32 {
         match &self {
             Range::Linear { min, max } => (plain - min) / (max - min),
+            Range::Skewed { min, max, factor } => ((plain - min) / (max - min)).powf(*factor),
+            Range::SymmetricalSkewed {
+                min,
+                max,
+                factor,
+                center,
+            } => {
+                // There's probably a much faster equivalent way to write this. Also, I have no clue
+                // how I managed to implement this correctly on the first try.
+                let unscaled_proportion = (plain - min) / (max - min);
+                let center_proportion = (center - min) / (max - min);
+                if unscaled_proportion > center_proportion {
+                    // The part above the center gets normalized to a [0, 1] range, skewed, and then
+                    // unnormalized and scaled back to the original [center_proportion, 1] range
+                    let scaled_proportion = (unscaled_proportion - center_proportion)
+                        * (1.0 - center_proportion).recip();
+                    (scaled_proportion.powf(*factor) * (1.0 - center_proportion))
+                        + center_proportion
+                } else {
+                    // The part below the center gets scaled, inverted (so the range is [0, 1] where
+                    // 0 corresponds to the center proportion and 1 corresponds to the orignal
+                    // normalized 0 value), skewed, inverted back again, and then scaled back to the
+                    // original range
+                    let inverted_scaled_proportion =
+                        (center_proportion - unscaled_proportion) * (center_proportion).recip();
+                    (1.0 - inverted_scaled_proportion.powf(*factor)) * (center_proportion)
+                }
+            }
         }
         .clamp(0.0, 1.0)
     }
@@ -59,6 +107,30 @@ impl NormalizebleRange<f32> for Range<f32> {
         let normalized = normalized.clamp(0.0, 1.0);
         match &self {
             Range::Linear { min, max } => (normalized * (max - min)) + min,
+            Range::Skewed { min, max, factor } => {
+                (normalized.powf(factor.recip()) * (max - min)) + min
+            }
+            Range::SymmetricalSkewed {
+                min,
+                max,
+                factor,
+                center,
+            } => {
+                // Reconstructing the subranges works the same as with the normal skewed ranges
+                let center_proportion = (center - min) / (max - min);
+                let skewed_proportion = if normalized > center_proportion {
+                    let scaled_proportion =
+                        (normalized - center_proportion) * (1.0 - center_proportion).recip();
+                    (scaled_proportion.powf(factor.recip()) * (1.0 - center_proportion))
+                        + center_proportion
+                } else {
+                    let inverted_scaled_proportion =
+                        (center_proportion - normalized) * (center_proportion).recip();
+                    (1.0 - inverted_scaled_proportion.powf(factor.recip())) * (center_proportion)
+                };
+
+                (skewed_proportion * (max - min)) + min
+            }
         }
     }
 }
@@ -67,6 +139,29 @@ impl NormalizebleRange<i32> for Range<i32> {
     fn normalize(&self, plain: i32) -> f32 {
         match &self {
             Range::Linear { min, max } => (plain - min) as f32 / (max - min) as f32,
+            Range::Skewed { min, max, factor } => {
+                ((plain - min) as f32 / (max - min) as f32).powf(*factor)
+            }
+            Range::SymmetricalSkewed {
+                min,
+                max,
+                factor,
+                center,
+            } => {
+                // See the comments in the float version
+                let unscaled_proportion = (plain - min) as f32 / (max - min) as f32;
+                let center_proportion = (center - min) as f32 / (max - min) as f32;
+                if unscaled_proportion > center_proportion {
+                    let scaled_proportion = (unscaled_proportion - center_proportion)
+                        * (1.0 - center_proportion).recip();
+                    (scaled_proportion.powf(*factor) * (1.0 - center_proportion))
+                        + center_proportion
+                } else {
+                    let inverted_scaled_proportion =
+                        (center_proportion - unscaled_proportion) * (center_proportion).recip();
+                    (1.0 - inverted_scaled_proportion.powf(*factor)) * (center_proportion)
+                }
+            }
         }
         .clamp(0.0, 1.0)
     }
@@ -75,6 +170,29 @@ impl NormalizebleRange<i32> for Range<i32> {
         let normalized = normalized.clamp(0.0, 1.0);
         match &self {
             Range::Linear { min, max } => (normalized * (max - min) as f32).round() as i32 + min,
+            Range::Skewed { min, max, factor } => {
+                (normalized.powf(factor.recip()) * (max - min) as f32).round() as i32 + min
+            }
+            Range::SymmetricalSkewed {
+                min,
+                max,
+                factor,
+                center,
+            } => {
+                let center_proportion = (center - min) as f32 / (max - min) as f32;
+                let skewed_proportion = if normalized > center_proportion {
+                    let scaled_proportion =
+                        (normalized - center_proportion) * (1.0 - center_proportion).recip();
+                    (scaled_proportion.powf(factor.recip()) * (1.0 - center_proportion))
+                        + center_proportion
+                } else {
+                    let inverted_scaled_proportion =
+                        (center_proportion - normalized) * (center_proportion).recip();
+                    (1.0 - inverted_scaled_proportion.powf(factor.recip())) * (center_proportion)
+                };
+
+                (skewed_proportion * (max - min) as f32).round() as i32 + min
+            }
         }
     }
 }
@@ -94,33 +212,174 @@ mod tests {
         Range::Linear { min: -10, max: 10 }
     }
 
-    #[test]
-    fn range_normalize_linear_float() {
-        let range = make_linear_float_range();
-        assert_eq!(range.normalize(17.5), 0.75);
+    fn make_skewed_float_range(factor: f32) -> Range<f32> {
+        Range::Skewed {
+            min: 10.0,
+            max: 20.0,
+            factor,
+        }
     }
 
-    #[test]
-    fn range_normalize_linear_int() {
-        let range = make_linear_int_range();
-        assert_eq!(range.normalize(-5), 0.25);
+    fn make_skewed_int_range(factor: f32) -> Range<i32> {
+        Range::Skewed {
+            min: -10,
+            max: 10,
+            factor,
+        }
     }
 
-    #[test]
-    fn range_unnormalize_linear_float() {
-        let range = make_linear_float_range();
-        assert_eq!(range.unnormalize(0.25), 12.5);
+    fn make_symmetrical_skewed_float_range(factor: f32) -> Range<f32> {
+        Range::SymmetricalSkewed {
+            min: 10.0,
+            max: 20.0,
+            factor,
+            center: 12.5,
+        }
     }
 
-    #[test]
-    fn range_unnormalize_linear_int() {
-        let range = make_linear_int_range();
-        assert_eq!(range.unnormalize(0.75), 5);
+    fn make_symmetrical_skewed_int_range(factor: f32) -> Range<i32> {
+        Range::SymmetricalSkewed {
+            min: -10,
+            max: 10,
+            factor,
+            center: -3,
+        }
     }
 
-    #[test]
-    fn range_unnormalize_linear_int_rounding() {
-        let range = make_linear_int_range();
-        assert_eq!(range.unnormalize(0.73), 5);
+    mod linear {
+        use super::super::*;
+        use super::*;
+
+        #[test]
+        fn range_normalize_float() {
+            let range = make_linear_float_range();
+            assert_eq!(range.normalize(17.5), 0.75);
+        }
+
+        #[test]
+        fn range_normalize_int() {
+            let range = make_linear_int_range();
+            assert_eq!(range.normalize(-5), 0.25);
+        }
+
+        #[test]
+        fn range_unnormalize_float() {
+            let range = make_linear_float_range();
+            assert_eq!(range.unnormalize(0.25), 12.5);
+        }
+
+        #[test]
+        fn range_unnormalize_int() {
+            let range = make_linear_int_range();
+            assert_eq!(range.unnormalize(0.75), 5);
+        }
+
+        #[test]
+        fn range_unnormalize_int_rounding() {
+            let range = make_linear_int_range();
+            assert_eq!(range.unnormalize(0.73), 5);
+        }
+    }
+
+    mod skewed {
+        use super::super::*;
+        use super::*;
+
+        #[test]
+        fn range_normalize_float() {
+            let range = make_skewed_float_range(Range::skew_factor(-2.0));
+            assert_eq!(range.normalize(17.5), 0.9306048591020996);
+        }
+
+        #[test]
+        fn range_normalize_int() {
+            let range = make_skewed_int_range(Range::skew_factor(-2.0));
+            assert_eq!(range.normalize(-5), 0.7071067811865476);
+        }
+
+        #[test]
+        fn range_unnormalize_float() {
+            let range = make_skewed_float_range(Range::skew_factor(-2.0));
+            assert_eq!(range.unnormalize(0.9306048591020996), 17.5);
+        }
+
+        #[test]
+        fn range_unnormalize_int() {
+            let range = make_skewed_int_range(Range::skew_factor(-2.0));
+            assert_eq!(range.unnormalize(0.7071067811865476), -5);
+        }
+
+        #[test]
+        fn range_normalize_linear_equiv_float() {
+            let linear_range = make_linear_float_range();
+            let skewed_range = make_skewed_float_range(1.0);
+            assert_eq!(linear_range.normalize(17.5), skewed_range.normalize(17.5));
+        }
+
+        #[test]
+        fn range_normalize_linear_equiv_int() {
+            let linear_range = make_linear_int_range();
+            let skewed_range = make_skewed_int_range(1.0);
+            assert_eq!(linear_range.normalize(-5), skewed_range.normalize(-5));
+        }
+
+        #[test]
+        fn range_unnormalize_linear_equiv_float() {
+            let linear_range = make_linear_float_range();
+            let skewed_range = make_skewed_float_range(1.0);
+            assert_eq!(
+                linear_range.unnormalize(0.25),
+                skewed_range.unnormalize(0.25)
+            );
+        }
+
+        #[test]
+        fn range_unnormalize_linear_equiv_int() {
+            let linear_range = make_linear_int_range();
+            let skewed_range = make_skewed_int_range(1.0);
+            assert_eq!(
+                linear_range.unnormalize(0.25),
+                skewed_range.unnormalize(0.25)
+            );
+        }
+
+        #[test]
+        fn range_unnormalize_linear_equiv_int_rounding() {
+            let linear_range = make_linear_int_range();
+            let skewed_range = make_skewed_int_range(1.0);
+            assert_eq!(
+                linear_range.unnormalize(0.73),
+                skewed_range.unnormalize(0.73)
+            );
+        }
+    }
+
+    mod symmetrical_skewed {
+        use super::super::*;
+        use super::*;
+
+        #[test]
+        fn range_normalize_float() {
+            let range = make_symmetrical_skewed_float_range(Range::skew_factor(-2.0));
+            assert_eq!(range.normalize(17.5), 0.9277015);
+        }
+
+        #[test]
+        fn range_normalize_int() {
+            let range = make_symmetrical_skewed_int_range(Range::skew_factor(-2.0));
+            assert_eq!(range.normalize(-5), 0.09411134);
+        }
+
+        #[test]
+        fn range_unnormalize_float() {
+            let range = make_symmetrical_skewed_float_range(Range::skew_factor(-2.0));
+            assert_eq!(range.unnormalize(0.9277015), 17.5);
+        }
+
+        #[test]
+        fn range_unnormalize_int() {
+            let range = make_symmetrical_skewed_int_range(Range::skew_factor(-2.0));
+            assert_eq!(range.unnormalize(0.09411134), -5);
+        }
     }
 }

src/wrapper/vst3.rs

@@ -636,6 +636,8 @@ impl<P: Plugin> IEditController for Wrapper<'_, P> {
                 ParamPtr::FloatParam(_) => 0,
                 ParamPtr::IntParam(p) => match (**p).range {
                     crate::param::Range::Linear { min, max } => max - min,
+                    crate::param::Range::Skewed { min, max, .. } => max - min,
+                    crate::param::Range::SymmetricalSkewed { min, max, .. } => max - min,
                 },
                 ParamPtr::BoolParam(_) => 1,
             };