Add explicit bypass parameter handling

Plugins can mark a `BoolParam` with `.is_bypass()`. Hosts can then link
use that parameter directly in their own UI.

README.md

@@ -66,6 +66,9 @@ for download links.
     `Params` object and annotating them with `#[persist = "key"]`.
   - Group your parameters into logical groups by nesting `Params` objects using
     the `#[nested = "Group Name"]`attribute.
+  - When needed, you can also provide your own implementation for the `Params`
+    trait to enable dynamically generated parameters and arrays of if mostly
+    identical parameter objects.
 - Stateful. Behaves mostly like JUCE, just without all of the boilerplate.
 - Does not make any assumptions on how you want to process audio, but does come
   with utilities and adapters to help with common access patterns.

src/param.rs

@@ -22,13 +22,18 @@ bitflags::bitflags! {
     #[repr(transparent)]
     #[derive(Default)]
     pub struct ParamFlags: u32 {
+        /// When applied to a [`BoolParam`], this will cause the parameter to be linked to the
+        /// host's bypass control. Only a single parameter can be marked as a bypass parameter. If
+        /// you don't have a bypass parameter, then NIH-plug will add one for you. You will need to
+        /// implement this yourself if your plugin introduces latency.
+        const BYPASS = 1 << 0;
         /// The parameter cannot be automated from the host. Setting this flag also prevents it from
         /// showing up in the host's own generic UI for this plugin. The parameter can still be
         /// changed from the plugin's editor GUI.
-        const NON_AUTOMATABLE = 1 << 0;
+        const NON_AUTOMATABLE = 1 << 1;
         /// Don't show this parameter when generating a generic UI for the plugin using one of
         /// NIH-plug's generic UI widgets.
-        const HIDE_IN_GENERIC_UI = 1 << 1;
+        const HIDE_IN_GENERIC_UI = 1 << 2;
     }
 }
 

src/param/boolean.rs

@@ -182,6 +182,15 @@ impl BoolParam {
         self
     }
 
+    /// Mark this parameter as a bypass parameter. Plugin hosts can integrate this parameter into
+    /// their UI. Only a single [`BoolParam`] can be a bypass parmaeter, and NIH-plug will add one
+    /// if you don't create one yourself. You will need to implement this yourself if your plugin
+    /// introduces latency.
+    pub fn is_bypass(mut self) -> Self {
+        self.flags.insert(ParamFlags::BYPASS);
+        self
+    }
+
     /// Mark the paramter as non-automatable. This means that the parameter cannot be automated from
     /// the host. Setting this flag also prevents it from showing up in the host's own generic UI
     /// for this plugin. The parameter can still be changed from the plugin's editor GUI.

src/plugin.rs

@@ -21,8 +21,6 @@ use crate::param::internals::Params;
 /// - Sidechain inputs
 /// - Multiple output busses
 /// - Special handling for offline processing
-/// - Bypass parameters, right now the plugin wrappers generates one for you but there's no way to
-///   interact with it yet
 /// - Outputting parameter changes from the plugin
 /// - MIDI CC handling
 /// - Outputting MIDI events from the process function (you can output parmaeter changes from an

src/wrapper/clap/wrapper.rs

@@ -48,7 +48,6 @@ use clap_sys::process::{
 use clap_sys::stream::{clap_istream, clap_ostream};
 use crossbeam::atomic::AtomicCell;
 use crossbeam::queue::ArrayQueue;
-use lazy_static::lazy_static;
 use parking_lot::RwLock;
 use raw_window_handle::RawWindowHandle;
 use std::any::Any;
@@ -75,15 +74,9 @@ use crate::plugin::{
 };
 use crate::util::permit_alloc;
 use crate::wrapper::state;
-use crate::wrapper::util::{hash_param_id, process_wrapper, strlcpy};
-
-/// Right now the wrapper adds its own bypass parameter.
-///
-/// TODO: Actually use this parameter.
-pub const BYPASS_PARAM_ID: &str = "bypass";
-lazy_static! {
-    pub static ref BYPASS_PARAM_HASH: u32 = hash_param_id(BYPASS_PARAM_ID);
-}
+use crate::wrapper::util::{
+    hash_param_id, process_wrapper, strlcpy, Bypass, BYPASS_PARAM_HASH, BYPASS_PARAM_ID,
+};
 
 /// How many output parameter changes we can store in our output parameter change queue. Storing
 /// more than this many parmaeters at a time will cause changes to get lost.
@@ -119,9 +112,9 @@ pub struct Wrapper<P: ClapPlugin> {
     /// The current buffer configuration, containing the sample rate and the maximum block size.
     /// Will be set in `clap_plugin::activate()`.
     current_buffer_config: AtomicCell<Option<BufferConfig>>,
-    /// Whether the plugin is currently bypassed. This is not yet integrated with the `Plugin`
-    /// trait.
-    bypass_state: AtomicBool,
+    /// Contains either a boolean indicating whether the plugin is currently bypassed, or a bypass
+    /// parameter if the plugin has one.
+    bypass: Bypass,
     /// The incoming events for the plugin, if `P::ACCEPTS_MIDI` is set.
     ///
     /// TODO: Maybe load these lazily at some point instead of needing to spool them all to this
@@ -345,10 +338,6 @@ impl<P: ClapPlugin> Wrapper<P> {
                 .iter()
                 .map(|(id, _, _, _)| id.clone())
                 .collect();
-            nih_debug_assert!(
-                !param_ids.contains(BYPASS_PARAM_ID),
-                "The wrapper already adds its own bypass parameter"
-            );
             nih_debug_assert_eq!(
                 param_map.len(),
                 param_ids.len(),
@@ -356,6 +345,31 @@ impl<P: ClapPlugin> Wrapper<P> {
             );
         }
 
+        // The plugin either supplies its own bypass parameter, or we'll create one for it
+        let mut bypass = Bypass::Dummy(AtomicBool::new(false));
+        for (id, _, ptr, _) in &param_id_hashes_ptrs_groups {
+            let flags = unsafe { ptr.flags() };
+            let is_bypass = flags.contains(ParamFlags::BYPASS);
+            if cfg!(debug_assertions) {
+                if id == BYPASS_PARAM_ID && !is_bypass {
+                    nih_debug_assert_failure!("Bypass parameters need to be marked with `.is_bypass()`, weird things will happen");
+                }
+                if is_bypass && matches!(bypass, Bypass::Parameter(_)) {
+                    nih_debug_assert_failure!(
+                        "Duplicate bypass parameters found, using the first one"
+                    );
+                    continue;
+                }
+            }
+
+            if is_bypass {
+                bypass = Bypass::Parameter(*ptr);
+                if !cfg!(debug_assertions) {
+                    break;
+                }
+            }
+        }
+
         let param_hashes = param_id_hashes_ptrs_groups
             .iter()
             .map(|(_, hash, _, _)| *hash)
@@ -439,7 +453,7 @@ impl<P: ClapPlugin> Wrapper<P> {
                 num_output_channels: P::DEFAULT_NUM_OUTPUTS,
             }),
             current_buffer_config: AtomicCell::new(None),
-            bypass_state: AtomicBool::new(false),
+            bypass,
             input_events: AtomicRefCell::new(VecDeque::with_capacity(512)),
             last_process_status: AtomicCell::new(ProcessStatus::Normal),
             current_latency: AtomicU32::new(0),
@@ -589,18 +603,21 @@ impl<P: ClapPlugin> Wrapper<P> {
         update: ClapParamUpdate,
         sample_rate: Option<f32>,
     ) -> bool {
-        if hash == *BYPASS_PARAM_HASH {
+        match (&self.bypass, self.param_by_hash.get(&hash)) {
+            (Bypass::Dummy(bypass_state), _) if hash == *BYPASS_PARAM_HASH => {
                 match update {
-                ClapParamUpdate::PlainValueSet(clap_plain_value) => self
-                    .bypass_state
-                    .store(clap_plain_value >= 0.5, Ordering::SeqCst),
+                    ClapParamUpdate::PlainValueSet(clap_plain_value) => {
+                        bypass_state.store(clap_plain_value >= 0.5, Ordering::SeqCst)
+                    }
                 }
 
                 true
-        } else if let Some(param_ptr) = self.param_by_hash.get(&hash) {
+            }
+            (_, Some(param_ptr)) => {
                 let normalized_value = match update {
                     ClapParamUpdate::PlainValueSet(clap_plain_value) => {
-                    clap_plain_value as f32 / unsafe { param_ptr.step_count() }.unwrap_or(1) as f32
+                        clap_plain_value as f32
+                            / unsafe { param_ptr.step_count() }.unwrap_or(1) as f32
                     }
                 };
 
@@ -614,8 +631,8 @@ impl<P: ClapPlugin> Wrapper<P> {
                 }
 
                 true
-        } else {
-            false
+            }
+            _ => false,
         }
     }
 
@@ -1170,16 +1187,20 @@ impl<P: ClapPlugin> Wrapper<P> {
                     }
                 }
 
-                // Only process audio if the plugin is not currently bypassed
-                let result = if !wrapper.bypass_state.load(Ordering::Relaxed) {
+                // Only process audio if the plugin isn't bypassed. If the plugin provides its
+                // own bypass parameter then it should decide what to do by itself.
+                let result = match &wrapper.bypass {
+                    Bypass::Dummy(bypass_state) if bypass_state.load(Ordering::Relaxed) => {
+                        wrapper.last_process_status.store(ProcessStatus::Normal);
+                        ProcessStatus::Normal
+                    }
+                    _ => {
                         let mut plugin = wrapper.plugin.write();
                         let mut context = wrapper.make_process_context(transport);
                         let result = plugin.process(&mut output_buffer, &mut context);
                         wrapper.last_process_status.store(result);
                         result
-                } else {
-                    wrapper.last_process_status.store(ProcessStatus::Normal);
-                    ProcessStatus::Normal
+                    }
                 };
 
                 let clap_result = match result {
@@ -1710,9 +1731,13 @@ impl<P: ClapPlugin> Wrapper<P> {
         check_null_ptr!(0, plugin);
         let wrapper = &*(plugin as *const Self);
 
-        // NOTE: We add a bypass parameter ourselves on index `plugin.param_hashes.len()`, so
-        //       these indices are all off by one
-        wrapper.param_hashes.len() as u32 + 1
+        // NOTE: We add a bypass parameter ourselves on index `self.inner.param_hashes.len()` if the
+        //       plugin does not provide its own bypass parmaeter, in which case these indices will
+        //       all be off by one
+        match wrapper.bypass {
+            Bypass::Parameter(_) => wrapper.param_hashes.len() as u32,
+            Bypass::Dummy(_) => wrapper.param_hashes.len() as u32 + 1,
+        }
     }
 
     unsafe extern "C" fn ext_params_get_info(
@@ -1723,8 +1748,7 @@ impl<P: ClapPlugin> Wrapper<P> {
         check_null_ptr!(false, plugin, param_info);
         let wrapper = &*(plugin as *const Self);
 
-        // Parameter index `self.param_ids.len()` is our own bypass parameter
-        if param_index < 0 || param_index > wrapper.param_hashes.len() as i32 {
+        if param_index < 0 || param_index > Self::ext_params_count(plugin) as i32 {
             return false;
         }
 
@@ -1733,7 +1757,9 @@ impl<P: ClapPlugin> Wrapper<P> {
         // TODO: We don't use the cookies at this point. In theory this would be faster than the ID
         //       hashmap lookup, but for now we'll stay consistent with the VST3 implementation.
         let param_info = &mut *param_info;
-        if param_index == wrapper.param_hashes.len() as i32 {
+        if matches!(wrapper.bypass, Bypass::Dummy(_))
+            && param_index == wrapper.param_hashes.len() as i32
+        {
             param_info.id = *BYPASS_PARAM_HASH;
             param_info.flags =
                 CLAP_PARAM_IS_STEPPED | CLAP_PARAM_IS_BYPASS | CLAP_PARAM_IS_AUTOMATABLE;
@@ -1749,7 +1775,9 @@ impl<P: ClapPlugin> Wrapper<P> {
             let param_ptr = &wrapper.param_by_hash[param_hash];
             let default_value = param_ptr.default_normalized_value();
             let step_count = param_ptr.step_count();
-            let automatable = !param_ptr.flags().contains(ParamFlags::NON_AUTOMATABLE);
+            let flags = param_ptr.flags();
+            let automatable = !flags.contains(ParamFlags::NON_AUTOMATABLE);
+            let is_bypass = flags.contains(ParamFlags::BYPASS);
 
             param_info.id = *param_hash;
             param_info.flags = if automatable {
@@ -1757,6 +1785,9 @@ impl<P: ClapPlugin> Wrapper<P> {
             } else {
                 CLAP_PARAM_IS_HIDDEN | CLAP_PARAM_IS_READONLY
             };
+            if is_bypass {
+                param_info.flags |= CLAP_PARAM_IS_BYPASS
+            }
             if step_count.is_some() {
                 param_info.flags |= CLAP_PARAM_IS_STEPPED
             }
@@ -1785,19 +1816,23 @@ impl<P: ClapPlugin> Wrapper<P> {
         check_null_ptr!(false, plugin, value);
         let wrapper = &*(plugin as *const Self);
 
-        if param_id == *BYPASS_PARAM_HASH {
-            *value = if wrapper.bypass_state.load(Ordering::SeqCst) {
+        match (&wrapper.bypass, wrapper.param_by_hash.get(&param_id)) {
+            (Bypass::Dummy(bypass_state), _) if param_id == *BYPASS_PARAM_HASH => {
+                *value = if bypass_state.load(Ordering::Relaxed) {
                     1.0
                 } else {
                     0.0
                 };
+
                 true
-        } else if let Some(param_ptr) = wrapper.param_by_hash.get(&param_id) {
-            *value =
-                param_ptr.normalized_value() as f64 * param_ptr.step_count().unwrap_or(1) as f64;
+            }
+            (_, Some(param_ptr)) => {
+                *value = param_ptr.normalized_value() as f64
+                    * param_ptr.step_count().unwrap_or(1) as f64;
+
                 true
-        } else {
-            false
+            }
+            _ => false,
         }
     }
 
@@ -1813,7 +1848,8 @@ impl<P: ClapPlugin> Wrapper<P> {
 
         let dest = std::slice::from_raw_parts_mut(display, size as usize);
 
-        if param_id == *BYPASS_PARAM_HASH {
+        match (&wrapper.bypass, wrapper.param_by_hash.get(&param_id)) {
+            (Bypass::Dummy(_), _) if param_id == *BYPASS_PARAM_HASH => {
                 if value > 0.5 {
                     strlcpy(dest, "Bypassed")
                 } else {
@@ -1821,7 +1857,8 @@ impl<P: ClapPlugin> Wrapper<P> {
                 }
 
                 true
-        } else if let Some(param_ptr) = wrapper.param_by_hash.get(&param_id) {
+            }
+            (_, Some(param_ptr)) => {
                 strlcpy(
                     dest,
                     // CLAP does not have a separate unit, so we'll include the unit here
@@ -1832,8 +1869,8 @@ impl<P: ClapPlugin> Wrapper<P> {
                 );
 
                 true
-        } else {
-            false
+            }
+            _ => false,
         }
     }
 
@@ -1851,16 +1888,21 @@ impl<P: ClapPlugin> Wrapper<P> {
             Err(_) => return false,
         };
 
-        if param_id == *BYPASS_PARAM_HASH {
-            let normalized_valeu = match display {
-                "Bypassed" => 1.0,
-                "Not Bypassed" => 0.0,
-                _ => return false,
+        match (&wrapper.bypass, wrapper.param_by_hash.get(&param_id)) {
+            (Bypass::Dummy(_), _) if param_id == *BYPASS_PARAM_HASH => {
+                let display = display.trim();
+                let normalized_valeu = if display.eq_ignore_ascii_case("bypassed") {
+                    1.0
+                } else if display.eq_ignore_ascii_case("not bypassed") {
+                    0.0
+                } else {
+                    return false;
                 };
                 *value = normalized_valeu;
 
                 true
-        } else if let Some(param_ptr) = wrapper.param_by_hash.get(&param_id) {
+            }
+            (_, Some(param_ptr)) => {
                 let normalized_value = match param_ptr.string_to_normalized_value(display) {
                     Some(v) => v as f64,
                     None => return false,
@@ -1868,8 +1910,8 @@ impl<P: ClapPlugin> Wrapper<P> {
                 *value = normalized_value * param_ptr.step_count().unwrap_or(1) as f64;
 
                 true
-        } else {
-            false
+            }
+            _ => false,
         }
     }
 
@@ -1901,8 +1943,7 @@ impl<P: ClapPlugin> Wrapper<P> {
             wrapper.plugin.read().params(),
             &wrapper.param_by_hash,
             &wrapper.param_id_to_hash,
-            BYPASS_PARAM_ID,
-            &wrapper.bypass_state,
+            &wrapper.bypass,
         );
         match serialized {
             Ok(serialized) => {
@@ -1964,8 +2005,7 @@ impl<P: ClapPlugin> Wrapper<P> {
             &wrapper.param_by_hash,
             &wrapper.param_id_to_hash,
             wrapper.current_buffer_config.load().as_ref(),
-            BYPASS_PARAM_ID,
-            &wrapper.bypass_state,
+            &wrapper.bypass,
         );
         if !success {
             return false;

src/wrapper/state.rs

@@ -3,8 +3,9 @@
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::pin::Pin;
-use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::atomic::Ordering;
 
+use super::util::{Bypass, BYPASS_PARAM_ID};
 use crate::param::internals::{ParamPtr, Params};
 use crate::param::Param;
 use crate::plugin::BufferConfig;
@@ -40,8 +41,7 @@ pub(crate) unsafe fn serialize(
     plugin_params: Pin<&dyn Params>,
     param_by_hash: &HashMap<u32, ParamPtr>,
     param_id_to_hash: &HashMap<String, u32>,
-    bypass_param_id: &str,
-    bypass_state: &AtomicBool,
+    bypass: &Bypass,
 ) -> serde_json::Result<Vec<u8>> {
     // We'll serialize parmaeter values as a simple `string_param_id: display_value` map.
     let mut params: HashMap<_, _> = param_id_to_hash
@@ -72,11 +72,13 @@ pub(crate) unsafe fn serialize(
         })
         .collect();
 
-    // Don't forget about the bypass parameter
+    // Don't forget about the bypass parameter if we added one for the plugin
+    if let Bypass::Dummy(bypass_state) = bypass {
         params.insert(
-        bypass_param_id.to_string(),
+            String::from(BYPASS_PARAM_ID),
             ParamValue::Bool(bypass_state.load(Ordering::SeqCst)),
         );
+    }
 
     // The plugin can also persist arbitrary fields alongside its parameters. This is useful for
     // storing things like sample data.
@@ -97,8 +99,7 @@ pub(crate) unsafe fn deserialize(
     param_by_hash: &HashMap<u32, ParamPtr>,
     param_id_to_hash: &HashMap<String, u32>,
     current_buffer_config: Option<&BufferConfig>,
-    bypass_param_id: &str,
-    bypass_state: &AtomicBool,
+    bypass: &Bypass,
 ) -> bool {
     let state: State = match serde_json::from_slice(state) {
         Ok(s) => s,
@@ -110,8 +111,9 @@ pub(crate) unsafe fn deserialize(
 
     let sample_rate = current_buffer_config.map(|c| c.sample_rate);
     for (param_id_str, param_value) in state.params {
-        // Handle the bypass parameter separately
-        if param_id_str == bypass_param_id {
+        // Handle the automatically generated bypass parameter separately
+        match bypass {
+            Bypass::Dummy(bypass_state) if param_id_str == BYPASS_PARAM_ID => {
                 match param_value {
                     ParamValue::Bool(b) => bypass_state.store(b, Ordering::SeqCst),
                     _ => nih_debug_assert_failure!(
@@ -122,7 +124,7 @@ pub(crate) unsafe fn deserialize(
                 };
                 continue;
             }
-
+            _ => {
                 let param_ptr = match param_id_to_hash
                     .get(param_id_str.as_str())
                     .and_then(|hash| param_by_hash.get(hash))
@@ -158,6 +160,8 @@ pub(crate) unsafe fn deserialize(
                     param_ptr.update_smoother(sample_rate, true);
                 }
             }
+        }
+    }
 
     // The plugin can also persist arbitrary fields alongside its parameters. This is useful for
     // storing things like sample data.

src/wrapper/util.rs

@@ -1,13 +1,36 @@
+use lazy_static::lazy_static;
 use std::cmp;
 use std::marker::PhantomData;
 use std::os::raw::c_char;
+use std::sync::atomic::AtomicBool;
 use vst3_sys::vst::TChar;
 use widestring::U16CString;
 
+use crate::param::internals::ParamPtr;
+
 #[cfg(all(debug_assertions, feature = "assert_process_allocs"))]
 #[global_allocator]
 static A: assert_no_alloc::AllocDisabler = assert_no_alloc::AllocDisabler;
 
+/// The ID of the automatically generated bypass parameter. Added if the plugin does not define its
+/// own bypass parameter.
+pub const BYPASS_PARAM_ID: &str = "bypass";
+lazy_static! {
+    pub static ref BYPASS_PARAM_HASH: u32 = hash_param_id(BYPASS_PARAM_ID);
+}
+
+/// The plugin's bypass parameter. If [`Plugin::params()`] contains a [`ParamFlags::BYPASS`]
+/// parameter then that will be used as the plugin's bypass parameter. Otherwise NIH-plug will add a
+/// dummy boolean parameter.
+#[derive(Debug)]
+pub enum Bypass {
+    /// A parameter from `P` that's marked as a bypass parameter.
+    Parameter(ParamPtr),
+    /// A boolean that keeps track of the plugin's bypass state. Added automatically if the plugin
+    /// doesn't have a bypass parameter.
+    Dummy(AtomicBool),
+}
+
 /// A Rabin fingerprint based string hash for parameter ID strings.
 pub fn hash_param_id(id: &str) -> u32 {
     let mut overflow;

src/wrapper/vst3/inner.rs

@@ -11,14 +11,15 @@ use vst3_sys::vst::IComponentHandler;
 
 use super::context::{WrapperGuiContext, WrapperProcessContext};
 use super::param_units::ParamUnits;
-use super::util::{ObjectPtr, VstPtr, BYPASS_PARAM_HASH, BYPASS_PARAM_ID};
+use super::util::{ObjectPtr, VstPtr};
 use super::view::WrapperView;
 use crate::buffer::Buffer;
 use crate::context::Transport;
 use crate::event_loop::{EventLoop, MainThreadExecutor, OsEventLoop};
 use crate::param::internals::ParamPtr;
+use crate::param::ParamFlags;
 use crate::plugin::{BufferConfig, BusConfig, Editor, NoteEvent, ProcessStatus, Vst3Plugin};
-use crate::wrapper::util::hash_param_id;
+use crate::wrapper::util::{hash_param_id, Bypass, BYPASS_PARAM_HASH, BYPASS_PARAM_ID};
 
 /// The actual wrapper bits. We need this as an `Arc<T>` so we can safely use our event loop API.
 /// Since we can't combine that with VST3's interior reference counting this just has to be moved to
@@ -56,9 +57,9 @@ pub(crate) struct WrapperInner<P: Vst3Plugin> {
     /// The current buffer configuration, containing the sample rate and the maximum block size.
     /// Will be set in `IAudioProcessor::setupProcessing()`.
     pub current_buffer_config: AtomicCell<Option<BufferConfig>>,
-    /// Whether the plugin is currently bypassed. This is not yet integrated with the `Plugin`
-    /// trait.
-    pub bypass_state: AtomicBool,
+    /// Contains either a boolean indicating whether the plugin is currently bypassed, or a bypass
+    /// parameter if the plugin has one.
+    pub bypass: Bypass,
     /// The last process status returned by the plugin. This is used for tail handling.
     pub last_process_status: AtomicCell<ProcessStatus>,
     /// The current latency in samples, as set by the plugin through the [`ProcessContext`].
@@ -153,10 +154,6 @@ impl<P: Vst3Plugin> WrapperInner<P> {
                 .iter()
                 .map(|(id, _, _, _)| id.clone())
                 .collect();
-            nih_debug_assert!(
-                !param_ids.contains(BYPASS_PARAM_ID),
-                "The wrapper already adds its own bypass parameter"
-            );
             nih_debug_assert_eq!(
                 param_map.len(),
                 param_ids.len(),
@@ -164,13 +161,38 @@ impl<P: Vst3Plugin> WrapperInner<P> {
             );
         }
 
+        // The plugin either supplies its own bypass parameter, or we'll create one for it
+        let mut bypass = Bypass::Dummy(AtomicBool::new(false));
+        for (id, _, ptr, _) in &param_id_hashes_ptrs_groups {
+            let flags = unsafe { ptr.flags() };
+            let is_bypass = flags.contains(ParamFlags::BYPASS);
+            if cfg!(debug_assertions) {
+                if id == BYPASS_PARAM_ID && !is_bypass {
+                    nih_debug_assert_failure!("Bypass parameters need to be marked with `.is_bypass()`, weird things will happen");
+                }
+                if is_bypass && matches!(bypass, Bypass::Parameter(_)) {
+                    nih_debug_assert_failure!(
+                        "Duplicate bypass parameters found, using the first one"
+                    );
+                    continue;
+                }
+            }
+
+            if is_bypass {
+                bypass = Bypass::Parameter(*ptr);
+                if !cfg!(debug_assertions) {
+                    break;
+                }
+            }
+        }
+
         let param_hashes = param_id_hashes_ptrs_groups
             .iter()
-            .map(|&(_, hash, _, _)| hash)
+            .map(|(_, hash, _, _)| *hash)
             .collect();
         let param_by_hash = param_id_hashes_ptrs_groups
             .iter()
-            .map(|&(_, hash, ptr, _)| (hash, ptr))
+            .map(|(_, hash, ptr, _)| (*hash, *ptr))
             .collect();
         let param_units = ParamUnits::from_param_groups(
             param_id_hashes_ptrs_groups
@@ -207,7 +229,7 @@ impl<P: Vst3Plugin> WrapperInner<P> {
                 num_output_channels: P::DEFAULT_NUM_OUTPUTS,
             }),
             current_buffer_config: AtomicCell::new(None),
-            bypass_state: AtomicBool::new(false),
+            bypass,
             last_process_status: AtomicCell::new(ProcessStatus::Normal),
             current_latency: AtomicU32::new(0),
             output_buffer: AtomicRefCell::new(Buffer::default()),
@@ -271,12 +293,13 @@ impl<P: Vst3Plugin> WrapperInner<P> {
         normalized_value: f32,
         sample_rate: Option<f32>,
     ) -> tresult {
-        if hash == *BYPASS_PARAM_HASH {
-            self.bypass_state
-                .store(normalized_value >= 0.5, Ordering::SeqCst);
+        match (&self.bypass, self.param_by_hash.get(&hash)) {
+            (Bypass::Dummy(bypass_state), _) if hash == *BYPASS_PARAM_HASH => {
+                bypass_state.store(normalized_value >= 0.5, Ordering::Relaxed);
 
                 kResultOk
-        } else if let Some(param_ptr) = self.param_by_hash.get(&hash) {
+            }
+            (_, Some(param_ptr)) => {
                 // Also update the parameter's smoothing if applicable
                 match (param_ptr, sample_rate) {
                     (_, Some(sample_rate)) => unsafe {
@@ -287,8 +310,8 @@ impl<P: Vst3Plugin> WrapperInner<P> {
                 }
 
                 kResultOk
-        } else {
-            kInvalidArgument
+            }
+            _ => kInvalidArgument,
         }
     }
 }

src/wrapper/vst3/util.rs

@@ -1,17 +1,6 @@
-use lazy_static::lazy_static;
 use std::ops::Deref;
 use vst3_sys::{interfaces::IUnknown, ComInterface};
 
-use crate::wrapper::util::hash_param_id;
-
-/// Right now the wrapper adds its own bypass parameter.
-///
-/// TODO: Actually use this parameter.
-pub const BYPASS_PARAM_ID: &str = "bypass";
-lazy_static! {
-    pub static ref BYPASS_PARAM_HASH: u32 = hash_param_id(BYPASS_PARAM_ID);
-}
-
 /// Early exit out of a VST3 function when one of the passed pointers is null
 macro_rules! check_null_ptr {
     ($ptr:expr $(, $ptrs:expr)* $(, )?) => {

src/wrapper/vst3/wrapper.rs

@@ -15,13 +15,13 @@ use vst3_sys::VST3;
 use widestring::U16CStr;
 
 use super::inner::WrapperInner;
-use super::util::{VstPtr, BYPASS_PARAM_HASH, BYPASS_PARAM_ID};
+use super::util::VstPtr;
 use super::view::WrapperView;
 use crate::context::Transport;
 use crate::param::ParamFlags;
 use crate::plugin::{BufferConfig, BusConfig, NoteEvent, ProcessStatus, Vst3Plugin};
 use crate::wrapper::state;
-use crate::wrapper::util::{process_wrapper, u16strlcpy};
+use crate::wrapper::util::{process_wrapper, u16strlcpy, Bypass, BYPASS_PARAM_HASH};
 use crate::wrapper::vst3::inner::ParameterChange;
 
 // Alias needed for the VST3 attribute macro
@@ -226,8 +226,7 @@ impl<P: Vst3Plugin> IComponent for Wrapper<P> {
             &self.inner.param_by_hash,
             &self.inner.param_id_to_hash,
             self.inner.current_buffer_config.load().as_ref(),
-            BYPASS_PARAM_ID,
-            &self.inner.bypass_state,
+            &self.inner.bypass,
         );
         if !success {
             return kResultFalse;
@@ -261,8 +260,7 @@ impl<P: Vst3Plugin> IComponent for Wrapper<P> {
             self.inner.plugin.read().params(),
             &self.inner.param_by_hash,
             &self.inner.param_id_to_hash,
-            BYPASS_PARAM_ID,
-            &self.inner.bypass_state,
+            &self.inner.bypass,
         );
         match serialized {
             Ok(serialized) => {
@@ -304,9 +302,13 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
     }
 
     unsafe fn get_parameter_count(&self) -> i32 {
-        // NOTE: We add a bypass parameter ourselves on index `self.inner.param_hashes.len()`, so
-        //       these indices are all off by one
-        self.inner.param_hashes.len() as i32 + 1
+        // NOTE: We add a bypass parameter ourselves on index `self.inner.param_hashes.len()` if the
+        //       plugin does not provide its own bypass parmaeter, in which case these indices will
+        //       all be off by one
+        match self.inner.bypass {
+            Bypass::Parameter(_) => self.inner.param_hashes.len() as i32,
+            Bypass::Dummy(_) => self.inner.param_hashes.len() as i32 + 1,
+        }
     }
 
     unsafe fn get_parameter_info(
@@ -316,15 +318,16 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
     ) -> tresult {
         check_null_ptr!(info);
 
-        // Parameter index `self.param_ids.len()` is our own bypass parameter
-        if param_index < 0 || param_index > self.inner.param_hashes.len() as i32 {
+        if param_index < 0 || param_index > self.get_parameter_count() {
             return kInvalidArgument;
         }
 
         *info = std::mem::zeroed();
 
         let info = &mut *info;
-        if param_index == self.inner.param_hashes.len() as i32 {
+        if matches!(self.inner.bypass, Bypass::Dummy(_))
+            && param_index == self.inner.param_hashes.len() as i32
+        {
             info.id = *BYPASS_PARAM_HASH;
             u16strlcpy(&mut info.title, "Bypass");
             u16strlcpy(&mut info.short_title, "Bypass");
@@ -343,7 +346,9 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
                 .expect("Inconsistent parameter data");
             let param_ptr = &self.inner.param_by_hash[param_hash];
             let default_value = param_ptr.default_normalized_value();
-            let automatable = !param_ptr.flags().contains(ParamFlags::NON_AUTOMATABLE);
+            let flags = param_ptr.flags();
+            let automatable = !flags.contains(ParamFlags::NON_AUTOMATABLE);
+            let is_bypass = flags.contains(ParamFlags::BYPASS);
 
             info.id = *param_hash;
             u16strlcpy(&mut info.title, param_ptr.name());
@@ -357,6 +362,9 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
             } else {
                 vst3_sys::vst::ParameterFlags::kIsReadOnly as i32 | (1 << 4) // kIsHidden
             };
+            if is_bypass {
+                info.flags |= vst3_sys::vst::ParameterFlags::kIsBypass as i32;
+            }
         }
 
         kResultOk
@@ -370,10 +378,10 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
     ) -> tresult {
         check_null_ptr!(string);
 
-        // Somehow there's no length there, so we'll assume our own maximum
         let dest = &mut *(string as *mut [TChar; 128]);
 
-        if id == *BYPASS_PARAM_HASH {
+        match (&self.inner.bypass, self.inner.param_by_hash.get(&id)) {
+            (Bypass::Dummy(_), _) if id == *BYPASS_PARAM_HASH => {
                 if value_normalized > 0.5 {
                     u16strlcpy(dest, "Bypassed")
                 } else {
@@ -381,15 +389,16 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
                 }
 
                 kResultOk
-        } else if let Some(param_ptr) = self.inner.param_by_hash.get(&id) {
+            }
+            (_, Some(param_ptr)) => {
                 u16strlcpy(
                     dest,
                     &param_ptr.normalized_value_to_string(value_normalized as f32, false),
                 );
 
                 kResultOk
-        } else {
-            kInvalidArgument
+            }
+            _ => kInvalidArgument,
         }
     }
 
@@ -406,16 +415,21 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
             Err(_) => return kInvalidArgument,
         };
 
-        if id == *BYPASS_PARAM_HASH {
-            let value = match string.as_str() {
-                "Bypassed" => 1.0,
-                "Not Bypassed" => 0.0,
-                _ => return kResultFalse,
+        match (&self.inner.bypass, self.inner.param_by_hash.get(&id)) {
+            (Bypass::Dummy(_), _) if id == *BYPASS_PARAM_HASH => {
+                let string = string.trim();
+                let value = if string.eq_ignore_ascii_case("bypassed") {
+                    1.0
+                } else if string.eq_ignore_ascii_case("not bypassed") {
+                    0.0
+                } else {
+                    return kInvalidArgument;
                 };
                 *value_normalized = value;
 
                 kResultOk
-        } else if let Some(param_ptr) = self.inner.param_by_hash.get(&id) {
+            }
+            (_, Some(param_ptr)) => {
                 let value = match param_ptr.string_to_normalized_value(&string) {
                     Some(v) => v as f64,
                     None => return kResultFalse,
@@ -423,42 +437,38 @@ impl<P: Vst3Plugin> IEditController for Wrapper<P> {
                 *value_normalized = value;
 
                 kResultOk
-        } else {
-            kInvalidArgument
+            }
+            _ => kInvalidArgument,
         }
     }
 
     unsafe fn normalized_param_to_plain(&self, id: u32, value_normalized: f64) -> f64 {
-        if id == *BYPASS_PARAM_HASH {
-            value_normalized
-        } else if let Some(param_ptr) = self.inner.param_by_hash.get(&id) {
-            param_ptr.preview_plain(value_normalized as f32) as f64
-        } else {
-            0.5
+        match (&self.inner.bypass, self.inner.param_by_hash.get(&id)) {
+            (Bypass::Dummy(_), _) if id == *BYPASS_PARAM_HASH => value_normalized.clamp(0.0, 1.0),
+            (_, Some(param_ptr)) => param_ptr.preview_plain(value_normalized as f32) as f64,
+            _ => 0.5,
         }
     }
 
     unsafe fn plain_param_to_normalized(&self, id: u32, plain_value: f64) -> f64 {
-        if id == *BYPASS_PARAM_HASH {
-            plain_value.clamp(0.0, 1.0)
-        } else if let Some(param_ptr) = self.inner.param_by_hash.get(&id) {
-            param_ptr.preview_normalized(plain_value as f32) as f64
-        } else {
-            0.5
+        match (&self.inner.bypass, self.inner.param_by_hash.get(&id)) {
+            (Bypass::Dummy(_), _) if id == *BYPASS_PARAM_HASH => plain_value.clamp(0.0, 1.0),
+            (_, Some(param_ptr)) => param_ptr.preview_normalized(plain_value as f32) as f64,
+            _ => 0.5,
         }
     }
 
     unsafe fn get_param_normalized(&self, id: u32) -> f64 {
-        if id == *BYPASS_PARAM_HASH {
-            if self.inner.bypass_state.load(Ordering::SeqCst) {
+        match (&self.inner.bypass, self.inner.param_by_hash.get(&id)) {
+            (Bypass::Dummy(bypass_state), _) if id == *BYPASS_PARAM_HASH => {
+                if bypass_state.load(Ordering::SeqCst) {
                     1.0
                 } else {
                     0.0
                 }
-        } else if let Some(param_ptr) = self.inner.param_by_hash.get(&id) {
-            param_ptr.normalized_value() as f64
-        } else {
-            0.5
+            }
+            (_, Some(param_ptr)) => param_ptr.normalized_value() as f64,
+            _ => 0.5,
         }
     }
 
@@ -921,8 +931,14 @@ impl<P: Vst3Plugin> IAudioProcessor for Wrapper<P> {
                     let mut plugin = self.inner.plugin.write();
                     let mut context = self.inner.make_process_context(transport);
 
-                    // Only process audio if the plugin isn't bypassed
-                    if !self.inner.bypass_state.load(Ordering::Relaxed) {
+                    // Only process audio if the plugin isn't bypassed. If the plugin provides its
+                    // own bypass parameter then it should decide what to do by itself.
+                    match &self.inner.bypass {
+                        Bypass::Dummy(bypass_state) if bypass_state.load(Ordering::Relaxed) => {
+                            self.inner.last_process_status.store(ProcessStatus::Normal);
+                            kResultOk
+                        }
+                        _ => {
                             let result = plugin.process(&mut output_buffer, &mut context);
                             self.inner.last_process_status.store(result);
                             match result {
@@ -933,9 +949,7 @@ impl<P: Vst3Plugin> IAudioProcessor for Wrapper<P> {
                                 }
                                 _ => kResultOk,
                             }
-                    } else {
-                        self.inner.last_process_status.store(ProcessStatus::Normal);
-                        kResultOk
+                        }
                     }
                 };