fix(plugins): step VST3 stepped params by 1/stepCount instead of 1 (#49)

src-tauri/src/audio/plugins/au_host.rs

@@ -727,10 +727,14 @@ fn param_info(unit: AudioUnit, id: u32) -> Option<PluginParamInfo> {
         max: info.maxValue as f64,
         default: info.defaultValue as f64,
         value: value as f64,
-        stepped: matches!(
+        step: if matches!(
             info.unit,
             AudioUnitParameterUnit::Indexed | AudioUnitParameterUnit::Boolean
-        ),
+        ) {
+            1.0
+        } else {
+            0.0
+        },
         read_only: !info
             .flags
             .contains(AudioUnitParameterOptions::Flag_IsWritable),
@@ -1271,7 +1275,7 @@ mod tests {
         assert_eq!((gain.min, gain.max), (-96.0, 24.0));
         assert!(!gain.read_only);
         assert!(
-            params.iter().any(|p| p.stepped),
+            params.iter().any(|p| p.step > 0.0),
             "no stepped parameter found"
         );
 

src-tauri/src/audio/plugins/clap_host.rs

@@ -368,7 +368,11 @@ impl ClapInstance {
                 max: info.max_value,
                 default: info.default_value,
                 value,
-                stepped: info.flags.contains(ParamInfoFlags::IS_STEPPED),
+                step: if info.flags.contains(ParamInfoFlags::IS_STEPPED) {
+                    1.0
+                } else {
+                    0.0
+                },
                 read_only: info.flags.contains(ParamInfoFlags::IS_READONLY),
             });
         }

src-tauri/src/audio/plugins/host_api.rs

@@ -34,8 +34,9 @@ pub struct PluginParamInfo {
     pub max: f64,
     pub default: f64,
     pub value: f64,
-    /// Stepped params (int/enum/toggle) render as discrete steps, not a slider.
-    pub stepped: bool,
+    /// One step in the `min..max` units for stepped params (int/enum/toggle),
+    /// 0 for continuous ones.
+    pub step: f64,
     /// Read-only params are shown but not editable.
     pub read_only: bool,
 }

src-tauri/src/audio/plugins/vst3_host.rs

@@ -205,7 +205,7 @@ impl Vst3Instance {
     pub fn params(&self) -> Vec<PluginParamInfo> {
         use vst3::Steinberg::Vst::ParameterInfo;
         use vst3::Steinberg::Vst::ParameterInfo_::ParameterFlags_::{
-            kIsHidden, kIsList, kIsProgramChange, kIsReadOnly,
+            kIsHidden, kIsProgramChange, kIsReadOnly,
         };
 
         let mut out = Vec::new();
@@ -228,7 +228,11 @@ impl Vst3Instance {
                     max: 1.0,
                     default: info.defaultNormalizedValue,
                     value: self.controller.getParamNormalized(info.id),
-                    stepped: info.stepCount > 0 || info.flags & kIsList != 0,
+                    step: if info.stepCount > 0 {
+                        1.0 / info.stepCount as f64
+                    } else {
+                        0.0
+                    },
                     read_only: info.flags & kIsReadOnly != 0,
                 });
             }
@@ -584,7 +588,7 @@ mod tests {
         let Some(param) = instance
             .params()
             .into_iter()
-            .find(|p| !p.read_only && !p.stepped)
+            .find(|p| !p.read_only && p.step == 0.0)
         else {
             panic!("{name} has no continuous writable parameter");
         };
@@ -650,7 +654,7 @@ mod tests {
         let param = before
             .params()
             .into_iter()
-            .find(|p| !p.read_only && !p.stepped)
+            .find(|p| !p.read_only && p.step == 0.0)
             .expect("a continuous parameter");
         let target = if param.value > 0.5 { 0.25 } else { 0.75 };
         before.set_param(param.id, target);

src/lib/modules/audio/types.ts

@@ -38,7 +38,7 @@ export interface PluginParam {
 	max: number;
 	default: number;
 	value: number;
-	stepped: boolean;
+	step: number;
 	readOnly: boolean;
 }
 

src/lib/modules/flow/ui/effect/plugin.svelte

@@ -242,7 +242,7 @@
 							value={p.value}
 							min={p.min}
 							max={p.max}
-							step={p.stepped ? 1 : p.max > p.min ? (p.max - p.min) / 100 : 0.01}
+							step={p.step || (p.max > p.min ? (p.max - p.min) / 100 : 0.01)}
 							defaultValue={p.default}
 							onChange={(v) => setParam(p, v)} />
 					{/each}