Implement step snapping for parameters

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

@@ -3,8 +3,8 @@ extern crate nih_plug;
 
 use atomic_float::AtomicF32;
 use nih_plug::{
-    formatters, util, Buffer, BufferConfig, BusConfig, Editor, IntParam, Plugin, ProcessContext,
-    ProcessStatus, Vst3Plugin,
+    util, Buffer, BufferConfig, BusConfig, Editor, IntParam, Plugin, ProcessContext, ProcessStatus,
+    Vst3Plugin,
 };
 use nih_plug::{FloatParam, Params, Range, SmoothingStyle};
 use nih_plug_egui::{create_egui_editor, egui, widgets, EguiState};

src/param.rs

@@ -34,18 +34,17 @@ pub trait Param: Display {
     /// Get the unnormalized value for this parameter.
     fn plain_value(&self) -> Self::Plain;
 
-    /// Set this parameter based on a plain, unnormalized value.
+    /// Set this parameter based on a plain, unnormalized value. This does **not** snap to step
+    /// sizes for continuous parameters (i.e. [FloatParam]).
     ///
     /// This does **not** update the smoother.
-    ///
-    /// TDOO: Decide on whether this should update the smoother or not. That wouldn't be compatible
-    /// with sample accurate automation when we add that.
     fn set_plain_value(&mut self, plain: Self::Plain);
 
     /// Get the normalized `[0, 1]` value for this parameter.
     fn normalized_value(&self) -> f32;
 
-    /// Set this parameter based on a normalized value.
+    /// Set this parameter based on a normalized value. This **does** snap to step sizes for
+    /// continuous parameters (i.e. [FloatParam]).
     ///
     /// This does **not** update the smoother.
     fn set_normalized_value(&mut self, normalized: f32);
@@ -63,7 +62,7 @@ pub trait Param: Display {
     fn preview_normalized(&self, plain: Self::Plain) -> f32;
 
     /// Get the plain, unnormalized value for a normalized value, as a float. Used as part of the
-    /// wrappers.
+    /// wrappers. This **does** snap to step sizes for continuous parameters (i.e. [FloatParam]).
     fn preview_plain(&self, normalized: f32) -> Self::Plain;
 
     /// Internal implementation detail for implementing [internals::Params]. This should not be used
@@ -251,7 +250,13 @@ macro_rules! impl_plainparam {
             }
 
             fn preview_plain(&self, normalized: f32) -> Self::Plain {
-                self.range.unnormalize(normalized)
+                let value = self.range.unnormalize(normalized);
+                match &self.step_size {
+                    // Step size snapping is not defined for [IntParam], so this cast is here just
+                    // so we can keep everything in this macro
+                    Some(step_size) => self.range.snap_to_step(value, *step_size as Self::Plain),
+                    None => value,
+                }
             }
 
             fn as_ptr(&self) -> internals::ParamPtr {

src/param/range.rs

@@ -31,6 +31,9 @@ impl Range<()> {
 
 /// A normalizable range for type `T`, where `self` is expected to be a type `R<T>`. Higher kinded
 /// types would have made this trait definition a lot clearer.
+///
+/// Floating point rounding to a step size is always done in the conversion from normalized to
+/// plain, inside [super::PlainParam::preview_plain].
 pub(crate) trait NormalizebleRange<T> {
     /// Normalize a plain, unnormalized value. Will be clamped to the bounds of the range if the
     /// normalized value exceeds `[0, 1]`.
@@ -39,6 +42,9 @@ pub(crate) trait NormalizebleRange<T> {
     /// Unnormalize a normalized value. Will be clamped to `[0, 1]` if the plain, unnormalized value
     /// would exceed that range.
     fn unnormalize(&self, normalized: f32) -> T;
+
+    /// Snap a vlue to a step size, clamping to the minimum and maximum value of the range.
+    fn snap_to_step(&self, value: T, step_size: T) -> T;
 }
 
 impl Default for Range<f32> {
@@ -116,6 +122,16 @@ impl NormalizebleRange<f32> for Range<f32> {
             }
         }
     }
+
+    fn snap_to_step(&self, value: f32, step_size: f32) -> f32 {
+        let (min, max) = match &self {
+            Range::Linear { min, max } => (min, max),
+            Range::Skewed { min, max, .. } => (min, max),
+            Range::SymmetricalSkewed { min, max, .. } => (min, max),
+        };
+
+        ((value / step_size).round() * step_size).clamp(*min, *max)
+    }
 }
 
 impl NormalizebleRange<i32> for Range<i32> {
@@ -175,6 +191,12 @@ impl NormalizebleRange<i32> for Range<i32> {
             }
         }
     }
+
+    fn snap_to_step(&self, value: i32, _step_size: i32) -> i32 {
+        // Integers are already discrete, and we don't allow setting step sizes on them through the
+        // builder interface
+        value
+    }
 }
 
 #[cfg(test)]
@@ -226,6 +248,20 @@ mod tests {
         }
     }
 
+    #[test]
+    fn step_size() {
+        // These are weird step sizes, but if it works here then it will work for anything
+        let range = make_linear_float_range();
+        assert_eq!(range.snap_to_step(13.0, 4.73), 14.49);
+    }
+
+    #[test]
+    fn step_size_clamping() {
+        let range = make_linear_float_range();
+        assert_eq!(range.snap_to_step(10.0, 4.73), 10.0);
+        assert_eq!(range.snap_to_step(20.0, 6.73), 20.0);
+    }
+
     mod linear {
         use super::super::*;
         use super::*;