Add stepping functions to Param

This can be useful for GUI widgets.

src/param.rs

@@ -30,9 +30,22 @@ pub trait Param: Display {
     /// Get the unit label for this parameter, if any.
     fn unit(&self) -> &'static str;
 
-    /// Get the number of steps for this paramter, if it is stepped. Used for the host's generic UI.
+    /// Get the number of steps for this paramter, if it is discrete. Used for the host's generic
+    /// UI.
     fn step_count(&self) -> Option<usize>;
 
+    /// Return the previous step from a specific value for this parameter. This can be the same as
+    /// `from` if the value is at the start of its range. This is mainly used for scroll wheel
+    /// interaction in plugin GUIs. When the parameter is not discrete then a step should cover one
+    /// hundredth of the normalized range instead.
+    fn previous_step(&self, from: Self::Plain) -> Self::Plain;
+
+    /// Return the next step from a specific value for this parameter. This can be the same as
+    /// `from` if the value is at the end of its range. This is mainly used for scroll wheel
+    /// interaction in plugin GUIs. When the parameter is not discrete then a step should cover one
+    /// hundredth of the normalized range instead.
+    fn next_step(&self, from: Self::Plain) -> Self::Plain;
+
     /// Get the unnormalized value for this parameter.
     fn plain_value(&self) -> Self::Plain;
 

src/param/boolean.rs

@@ -66,6 +66,14 @@ impl Param for BoolParam {
         Some(1)
     }
 
+    fn previous_step(&self, _from: Self::Plain) -> Self::Plain {
+        false
+    }
+
+    fn next_step(&self, _from: Self::Plain) -> Self::Plain {
+        true
+    }
+
     fn plain_value(&self) -> Self::Plain {
         self.value
     }

src/param/enums.rs

@@ -113,6 +113,14 @@ impl<T: Enum + PartialEq> Param for EnumParam<T> {
         self.inner.step_count()
     }
 
+    fn previous_step(&self, from: Self::Plain) -> Self::Plain {
+        T::from_index(self.inner.previous_step(T::to_index(from) as i32) as usize)
+    }
+
+    fn next_step(&self, from: Self::Plain) -> Self::Plain {
+        T::from_index(self.inner.next_step(T::to_index(from) as i32) as usize)
+    }
+
     fn plain_value(&self) -> Self::Plain {
         T::from_index(self.inner.plain_value() as usize)
     }
@@ -174,6 +182,14 @@ impl Param for EnumParamInner {
         Some(self.len() - 1)
     }
 
+    fn previous_step(&self, from: Self::Plain) -> Self::Plain {
+        self.inner.previous_step(from)
+    }
+
+    fn next_step(&self, from: Self::Plain) -> Self::Plain {
+        self.inner.next_step(from)
+    }
+
     fn plain_value(&self) -> Self::Plain {
         self.inner.plain_value()
     }

src/param/float.rs

@@ -107,6 +107,29 @@ impl Param for FloatParam {
         None
     }
 
+    fn previous_step(&self, from: Self::Plain) -> Self::Plain {
+        // This one's slightly more involved. We'll split the normalized range up into 100 segments,
+        // but if `self.step_size` is set then we'll use that. Ideally we might want to split the
+        // range up into at most 100 segments, falling back to the step size if the total number of
+        // steps would be smaller than that, but since ranges can be nonlienar that's a bit
+        // difficult to pull off.
+        // TODO: At some point, implement the above mentioned step size quantization
+        match self.step_size {
+            Some(step_size) => from - step_size,
+            None => self.preview_plain(self.preview_normalized(from) - 0.01),
+        }
+        .clamp(self.range.min(), self.range.max())
+    }
+
+    fn next_step(&self, from: Self::Plain) -> Self::Plain {
+        // See above
+        match self.step_size {
+            Some(step_size) => from + step_size,
+            None => self.preview_plain(self.preview_normalized(from) + 0.01),
+        }
+        .clamp(self.range.min(), self.range.max())
+    }
+
     fn plain_value(&self) -> Self::Plain {
         self.value
     }

src/param/integer.rs

@@ -95,7 +95,15 @@ impl Param for IntParam {
     }
 
     fn step_count(&self) -> Option<usize> {
-        self.range.step_count()
+        Some(self.range.step_count())
+    }
+
+    fn previous_step(&self, from: Self::Plain) -> Self::Plain {
+        (from - 1).clamp(self.range.min(), self.range.max())
+    }
+
+    fn next_step(&self, from: Self::Plain) -> Self::Plain {
+        (from + 1).clamp(self.range.min(), self.range.max())
     }
 
     fn plain_value(&self) -> Self::Plain {

src/param/range.rs

@@ -118,6 +118,24 @@ impl FloatRange {
         }
     }
 
+    /// The minimum value in this range.
+    pub fn min(&self) -> f32 {
+        match self {
+            FloatRange::Linear { min, .. }
+            | FloatRange::Skewed { min, .. }
+            | FloatRange::SymmetricalSkewed { min, .. } => *min,
+        }
+    }
+
+    /// The maximum value in this range.
+    pub fn max(&self) -> f32 {
+        match self {
+            FloatRange::Linear { max, .. }
+            | FloatRange::Skewed { max, .. }
+            | FloatRange::SymmetricalSkewed { max, .. } => *max,
+        }
+    }
+
     /// Snap a vlue to a step size, clamping to the minimum and maximum value of the range.
     pub fn snap_to_step(&self, value: f32, step_size: f32) -> f32 {
         let (min, max) = match &self {
@@ -149,10 +167,24 @@ impl IntRange {
         }
     }
 
-    /// The number of steps in this range, if it is stepped. Used for the host's generic UI.
-    pub fn step_count(&self) -> Option<usize> {
+    /// The minimum value in this range.
+    pub fn min(&self) -> i32 {
         match self {
-            IntRange::Linear { min, max } => Some((max - min) as usize),
+            IntRange::Linear { min, .. } => *min,
+        }
+    }
+
+    /// The maximum value in this range.
+    pub fn max(&self) -> i32 {
+        match self {
+            IntRange::Linear { max, .. } => *max,
+        }
+    }
+
+    /// The number of steps in this range. Used for the host's generic UI.
+    pub fn step_count(&self) -> usize {
+        match self {
+            IntRange::Linear { min, max } => (max - min) as usize,
         }
     }
 }