Merge #315

Cargo.lock

@@ -3482,6 +3482,7 @@ dependencies = [
  "serde",
  "soundcraft-dsp",
  "thiserror 2.0.21",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -3640,6 +3641,7 @@ dependencies = [
  "soundcraft-dsp",
  "thiserror 2.0.21",
  "vst3",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]

ROADMAP.md

@@ -122,6 +122,7 @@ mutated and truncated movies. Field reports from the first public week are track
 
 ## Progress log
 
+- **2026-10-12 (plugin editors on Windows):** VST3 editors and embedded CLAP editors open in a SoundCraft host window on Windows (owned by the app window, resized on request, closed from its title bar); verified with a JUCE VST3 compressor and a CLAP effect. No readiness percentage change.
 - **2026-10-12:** `soundcraft-cli convert` rejects an unparsable or zero `--rate` and an unknown `--bit-depth` (exit 1, nothing written) instead of converting with a default (#256)
 - **2026-10-12:** Timecode labels with huge fields no longer overflow: frame counts are computed in 128 bits and clamp, so `setup.current_timecode` and `session.format_time` saturate instead of failing (#248)
 - **2026-10-12:** `session.format_time` with the smallest bar number no longer fails with an internal error: the bar offset saturates (#249)

crates/clap-host/Cargo.toml

@@ -13,6 +13,10 @@ serde.workspace = true
 thiserror.workspace = true
 log.workspace = true
 
+# The Windows host window for embedded editors (a top-level HWND the plugin parents its GUI in).
+[target.'cfg(windows)'.dependencies]
+windows-sys = { version = "0.61", features = ["Win32_Foundation", "Win32_Graphics_Gdi", "Win32_System_LibraryLoader", "Win32_UI_Input_KeyboardAndMouse", "Win32_UI_WindowsAndMessaging"] }
+
 [[test]]
 name = "editor_main_thread"
 harness = false

crates/clap-host/src/ffi.rs

@@ -20,7 +20,7 @@ use clap_sys::events::{
     clap_event_transport, clap_input_events, clap_output_events,
 };
 use clap_sys::ext::audio_ports::{CLAP_AUDIO_PORT_IS_MAIN, CLAP_EXT_AUDIO_PORTS, clap_audio_port_info, clap_plugin_audio_ports};
-use clap_sys::ext::gui::{CLAP_EXT_GUI, clap_host_gui, clap_plugin_gui};
+use clap_sys::ext::gui::{CLAP_EXT_GUI, clap_host_gui, clap_plugin_gui, clap_window, clap_window_handle};
 use clap_sys::ext::latency::{CLAP_EXT_LATENCY, clap_host_latency, clap_plugin_latency};
 use clap_sys::ext::log::{CLAP_EXT_LOG, CLAP_LOG_ERROR, CLAP_LOG_FATAL, CLAP_LOG_WARNING, clap_host_log, clap_log_severity};
 use clap_sys::ext::note_ports::{CLAP_EXT_NOTE_PORTS, clap_note_port_info, clap_plugin_note_ports};
@@ -40,7 +40,7 @@ use soundcraft_dsp::Transport;
 use std::collections::HashMap;
 use std::ffi::{CStr, CString, c_char, c_void};
 use std::path::{Path, PathBuf};
-use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex, OnceLock, PoisonError};
 
 /// Most plugins one factory may report (hostile-input cap).
@@ -279,7 +279,7 @@ impl Bundle {
         inst.state_ext = inst.extension::<clap_plugin_state>(CLAP_EXT_STATE);
         let gui = inst.extension::<clap_plugin_gui>(CLAP_EXT_GUI);
         inst.gui = Arc::new(GuiLink {
-            inner: Mutex::new(GuiInner { plugin, gui, state: inst.state_ext, alive: true, created: false, visible: false }),
+            inner: Mutex::new(GuiInner { plugin, gui, state: inst.state_ext, alive: true, created: false, visible: false, window: None }),
             host: Arc::clone(&inst.state),
         });
         Ok(inst)
@@ -314,6 +314,8 @@ pub(crate) struct HostState {
     pub gui_destroyed: AtomicBool,
     pub gui_show: AtomicBool,
     pub gui_hide: AtomicBool,
+    /// A size an embedded editor asked for (`width << 32 | height`; 0 = none pending).
+    pub gui_resize: AtomicU64,
     /// Parameter changes the plugin reported (output events: typically edits in its GUI),
     /// waiting for the UI. Bounded by `EDIT_CAP`; the audio thread only `try_lock`s it.
     pub edits: Mutex<Vec<(u32, f64)>>,
@@ -332,6 +334,7 @@ impl Default for HostState {
             gui_destroyed: AtomicBool::new(false),
             gui_show: AtomicBool::new(false),
             gui_hide: AtomicBool::new(false),
+            gui_resize: AtomicU64::new(0),
             edits: Mutex::new(Vec::with_capacity(EDIT_CAP)),
         }
     }
@@ -412,8 +415,16 @@ unsafe extern "C" fn host_state_mark_dirty(host: *const clap_host) {
 
 unsafe extern "C" fn host_gui_resize_hints_changed(_host: *const clap_host) {}
 
-unsafe extern "C" fn host_gui_request_resize(_host: *const clap_host, _width: u32, _height: u32) -> bool {
-    // Floating windows belong to the plugin, which resizes them itself.
+unsafe extern "C" fn host_gui_request_resize(host: *const clap_host, width: u32, height: u32) -> bool {
+    // Floating windows belong to the plugin, which resizes them itself; an embedded editor's host
+    // window is resized by the editor's `idle` on the main thread.
+    // SAFETY: the plugin passes back the host pointer we gave it.
+    if let Some(s) = unsafe { state(host) }
+        && width > 0
+        && height > 0
+    {
+        s.gui_resize.store((u64::from(width) << 32) | u64::from(height), Ordering::Relaxed);
+    }
     true
 }
 
@@ -739,6 +750,8 @@ struct GuiInner {
     alive: bool,
     created: bool,
     visible: bool,
+    /// The host window of an embedded editor (`None` for floating editors).
+    window: Option<hostwin::HostWindow>,
 }
 
 /// The link between an instance and its editor and state handles. The instance may process on
@@ -762,6 +775,7 @@ impl Default for GuiLink {
                 alive: false,
                 created: false,
                 visible: false,
+                window: None,
             }),
             host: Arc::new(HostState::default()),
         }
@@ -803,6 +817,9 @@ impl GuiLink {
                 // SAFETY: live plugin with a created GUI; main thread (checked).
                 unsafe { show(g.plugin) };
             }
+            if let Some(w) = &g.window {
+                w.raise();
+            }
             g.visible = true;
             return Ok(());
         }
@@ -810,7 +827,11 @@ impl GuiLink {
         let (Some(supported), Some(create)) = (vt.is_api_supported, vt.create) else { return Err("incomplete clap.gui extension".into()) };
         // SAFETY: live plugin; `api` is a static NUL-terminated string; main thread.
         if !unsafe { supported(g.plugin, api.as_ptr(), true) } {
-            return Err("this plugin offers only an embedded editor; SoundCraft hosts floating CLAP editors".into());
+            // SAFETY: as above.
+            if hostwin::SUPPORTED && unsafe { supported(g.plugin, api.as_ptr(), false) } {
+                return self.open_embedded(&mut g, vt, api, title);
+            }
+            return Err("this plugin offers only an embedded editor, which SoundCraft hosts on Windows only".into());
         }
         self.host.gui_closed.store(false, Ordering::Relaxed);
         self.host.gui_destroyed.store(false, Ordering::Relaxed);
@@ -842,6 +863,61 @@ impl GuiLink {
         Ok(())
     }
 
+    /// Embeds the editor in a host window of ours (plugins that offer no floating editor).
+    fn open_embedded(&self, g: &mut GuiInner, vt: clap_plugin_gui, api: &CStr, title: &str) -> Result<(), String> {
+        let (Some(create), Some(set_parent)) = (vt.create, vt.set_parent) else { return Err("incomplete clap.gui extension".into()) };
+        self.host.gui_closed.store(false, Ordering::Relaxed);
+        self.host.gui_destroyed.store(false, Ordering::Relaxed);
+        self.host.gui_resize.store(0, Ordering::Relaxed);
+        // SAFETY: live plugin; `api` is a static NUL-terminated string; main thread; no GUI yet.
+        if !unsafe { create(g.plugin, api.as_ptr(), false) } {
+            return Err("the plugin could not create its editor".into());
+        }
+        g.created = true;
+        if let Some(f) = vt.set_scale {
+            // SAFETY: live plugin with a created GUI.
+            unsafe { f(g.plugin, 1.0) };
+        }
+        let (mut w, mut h) = (640u32, 480u32);
+        if let Some(f) = vt.get_size {
+            let (mut a, mut b) = (0u32, 0u32);
+            // SAFETY: live plugin with a created GUI; both out-pointers are valid locals.
+            if unsafe { f(g.plugin, &mut a, &mut b) } && a > 0 && b > 0 {
+                (w, h) = (a.min(16_384), b.min(16_384));
+            }
+        }
+        let win = match hostwin::HostWindow::new(title, f64::from(w), f64::from(h)) {
+            Ok(win) => win,
+            Err(e) => {
+                GuiLink::destroy(g);
+                return Err(e);
+            }
+        };
+        let parent = clap_window { api: api.as_ptr(), specific: clap_window_handle { win32: win.parent() } };
+        // SAFETY: live plugin with a created embedded GUI; `parent` names our live window and
+        // outlives the call.
+        if !unsafe { set_parent(g.plugin, &parent) } {
+            win.close();
+            GuiLink::destroy(g);
+            return Err("the editor could not attach to its window".into());
+        }
+        g.window = Some(win);
+        let shown = match vt.show {
+            // SAFETY: live plugin with a created, parented GUI.
+            Some(f) => unsafe { f(g.plugin) },
+            None => true,
+        };
+        if !shown {
+            GuiLink::destroy(g);
+            return Err("the plugin could not show its editor".into());
+        }
+        if let Some(win) = &g.window {
+            win.raise();
+        }
+        g.visible = true;
+        Ok(())
+    }
+
     fn destroy(g: &mut GuiInner) {
         if g.created
             && let Some(f) = GuiLink::vt(g).and_then(|v| v.destroy)
@@ -851,6 +927,10 @@ impl GuiLink {
         }
         g.created = false;
         g.visible = false;
+        // The plugin's child window is gone; now its host window can go too.
+        if let Some(w) = g.window.take() {
+            w.close();
+        }
     }
 
     /// `clap_plugin_state.save` into memory (`None` without the extension, on failure, or once the
@@ -879,7 +959,7 @@ impl GuiLink {
 
     pub fn is_open(&self) -> bool {
         let g = self.lock();
-        g.alive && g.created && g.visible
+        g.alive && g.created && g.visible && g.window.as_ref().is_none_or(hostwin::HostWindow::is_visible)
     }
 
     /// Main-thread housekeeping: runs a requested `on_main_thread`, follows the plugin's
@@ -900,7 +980,21 @@ impl GuiLink {
             }
         }
         if g.created {
-            if self.host.gui_closed.swap(false, Ordering::Relaxed) {
+            let resize = self.host.gui_resize.swap(0, Ordering::Relaxed);
+            if resize != 0
+                && let Some(win) = &g.window
+            {
+                let (w, h) = ((resize >> 32) as u32, resize as u32);
+                hostwin::resize(win.raw(), f64::from(w), f64::from(h));
+                if let Some(f) = GuiLink::vt(&g).and_then(|v| v.set_size) {
+                    // SAFETY: live plugin with a created embedded GUI, main thread.
+                    unsafe { f(g.plugin, w, h) };
+                }
+            }
+            if g.window.as_ref().is_some_and(|w| !w.is_visible()) {
+                // The user closed the embedded editor's host window: free the editor.
+                GuiLink::destroy(&mut g);
+            } else if self.host.gui_closed.swap(false, Ordering::Relaxed) {
                 // The user closed the floating window (or the plugin lost its GUI): free it.
                 self.host.gui_destroyed.store(false, Ordering::Relaxed);
                 GuiLink::destroy(&mut g);
@@ -936,6 +1030,8 @@ impl GuiLink {
             } else {
                 log::warn!("clap: editor still open while its plugin is destroyed off the main thread");
                 g.created = false;
+                // Window calls are main-thread only: leave the host window rather than crash.
+                g.window = None;
             }
         }
         g.alive = false;
@@ -1326,6 +1422,210 @@ impl Drop for Instance {
     }
 }
 
+// ---- host window for embedded editors ------------------------------------------------------
+
+/// The Windows host window for embedded editors: a top-level window owned by the app's active
+/// window (no taskbar button) whose client area is the plugin's parent `HWND`. Closing it only
+/// hides it; the editor link notices in `idle`, destroys the plugin's GUI, then the window.
+/// Messages are dispatched by the app's own event loop on the main thread.
+#[cfg(windows)]
+mod hostwin {
+    use std::ffi::c_void;
+    use std::sync::OnceLock;
+    use windows_sys::Win32::Foundation::{HWND, LPARAM, LRESULT, RECT, WPARAM};
+    use windows_sys::Win32::System::LibraryLoader::GetModuleHandleW;
+    use windows_sys::Win32::UI::Input::KeyboardAndMouse::GetActiveWindow;
+    use windows_sys::Win32::UI::WindowsAndMessaging::{
+        AdjustWindowRectEx, CS_HREDRAW, CS_VREDRAW, CW_USEDEFAULT, CreateWindowExW, DefWindowProcW, DestroyWindow, GWL_EXSTYLE, GWL_STYLE,
+        GetWindowLongPtrW, IDC_ARROW, IsWindow, IsWindowVisible, LoadCursorW, RegisterClassExW, SW_HIDE, SW_SHOW, SWP_NOACTIVATE, SWP_NOMOVE,
+        SWP_NOZORDER, SetForegroundWindow, SetWindowPos, ShowWindow, WM_CLOSE, WNDCLASSEXW, WS_CAPTION, WS_CLIPCHILDREN, WS_OVERLAPPED, WS_SYSMENU,
+    };
+
+    pub const SUPPORTED: bool = true;
+
+    /// Rust names the process's first thread "main"; the app runs its UI (and message loop) there.
+    fn on_main_thread() -> bool {
+        std::thread::current().name() == Some("main")
+    }
+
+    fn wide(s: &str) -> Vec<u16> {
+        s.encode_utf16().filter(|&c| c != 0).chain(Some(0)).collect()
+    }
+
+    const STYLE: u32 = WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_CLIPCHILDREN;
+
+    unsafe extern "system" fn wndproc(hwnd: HWND, msg: u32, wparam: WPARAM, lparam: LPARAM) -> LRESULT {
+        if msg == WM_CLOSE {
+            // SAFETY: `hwnd` is the window this procedure was called for.
+            unsafe { ShowWindow(hwnd, SW_HIDE) };
+            return 0;
+        }
+        // SAFETY: default handling of a message for the window it was sent to.
+        unsafe { DefWindowProcW(hwnd, msg, wparam, lparam) }
+    }
+
+    /// Registers the window class once; the name lives for the whole process.
+    fn class_name() -> Option<&'static [u16]> {
+        static CLASS: OnceLock<Option<Vec<u16>>> = OnceLock::new();
+        CLASS
+            .get_or_init(|| {
+                let name = wide("SoundCraftClapEditor");
+                // SAFETY: null asks for this process's module handle.
+                let instance = unsafe { GetModuleHandleW(std::ptr::null()) };
+                let wc = WNDCLASSEXW {
+                    cbSize: std::mem::size_of::<WNDCLASSEXW>() as u32,
+                    style: CS_HREDRAW | CS_VREDRAW,
+                    lpfnWndProc: Some(wndproc),
+                    cbClsExtra: 0,
+                    cbWndExtra: 0,
+                    hInstance: instance,
+                    hIcon: std::ptr::null_mut(),
+                    // SAFETY: a system cursor (null instance + predefined id).
+                    hCursor: unsafe { LoadCursorW(std::ptr::null_mut(), IDC_ARROW) },
+                    hbrBackground: std::ptr::null_mut(),
+                    lpszMenuName: std::ptr::null(),
+                    lpszClassName: name.as_ptr(),
+                    hIconSm: std::ptr::null_mut(),
+                };
+                // SAFETY: a fully initialised class description whose strings outlive the call
+                // (the name is kept for the process lifetime in this `OnceLock`).
+                (unsafe { RegisterClassExW(&wc) } != 0).then_some(name)
+            })
+            .as_deref()
+    }
+
+    /// Outer window size for a client area of `w`×`h`.
+    fn outer_size(style: u32, ex_style: u32, w: f64, h: f64) -> (i32, i32) {
+        let mut r = RECT { left: 0, top: 0, right: w as i32, bottom: h as i32 };
+        // SAFETY: `r` is a valid, writable rect.
+        unsafe { AdjustWindowRectEx(&mut r, style, 0, ex_style) };
+        (r.right.saturating_sub(r.left), r.bottom.saturating_sub(r.top))
+    }
+
+    /// Owns the window handle; destroyed in `close` (main thread only).
+    pub struct HostWindow {
+        hwnd: HWND,
+    }
+
+    // SAFETY: the handle is only used on the main thread (every method checks); the struct
+    // merely carries it between threads' locks.
+    unsafe impl Send for HostWindow {}
+
+    impl HostWindow {
+        fn live(&self) -> Option<HWND> {
+            // SAFETY: `IsWindow` accepts any value and only reports whether it names a window.
+            (on_main_thread() && unsafe { IsWindow(self.hwnd) } != 0).then_some(self.hwnd)
+        }
+
+        pub fn new(title: &str, w: f64, h: f64) -> Result<HostWindow, String> {
+            if !on_main_thread() {
+                return Err("plugin editors must be opened on the main thread".into());
+            }
+            let class = class_name().ok_or_else(|| "cannot register the editor window class".to_string())?;
+            let title = wide(title);
+            let (ow, oh) = outer_size(STYLE, 0, w, h);
+            // SAFETY: main thread; the active window (or null) of this thread's queue.
+            let owner = unsafe { GetActiveWindow() };
+            // SAFETY: registered class and NUL-terminated strings that outlive the call; the
+            // owner is null or a window of this thread.
+            let hwnd = unsafe {
+                CreateWindowExW(
+                    0,
+                    class.as_ptr(),
+                    title.as_ptr(),
+                    STYLE,
+                    CW_USEDEFAULT,
+                    CW_USEDEFAULT,
+                    ow,
+                    oh,
+                    owner,
+                    std::ptr::null_mut(),
+                    GetModuleHandleW(std::ptr::null()),
+                    std::ptr::null(),
+                )
+            };
+            if hwnd.is_null() {
+                return Err("cannot create the editor window".into());
+            }
+            Ok(HostWindow { hwnd })
+        }
+
+        /// The window handle (for resizes).
+        pub fn raw(&self) -> *mut c_void {
+            self.hwnd
+        }
+
+        /// The `HWND` the plugin creates its child window in.
+        pub fn parent(&self) -> *mut c_void {
+            self.live().unwrap_or(std::ptr::null_mut())
+        }
+
+        pub fn raise(&self) {
+            if let Some(h) = self.live() {
+                // SAFETY: a live window of this thread.
+                unsafe {
+                    ShowWindow(h, SW_SHOW);
+                    SetForegroundWindow(h);
+                }
+            }
+        }
+
+        pub fn is_visible(&self) -> bool {
+            // SAFETY: a live window of this thread.
+            self.live().is_some_and(|h| unsafe { IsWindowVisible(h) } != 0)
+        }
+
+        pub fn close(self) {
+            if let Some(h) = self.live() {
+                // SAFETY: our own live window; the plugin's GUI was destroyed first.
+                unsafe { DestroyWindow(h) };
+            }
+        }
+    }
+
+    /// Resizes a host window's client area (`window` from [`HostWindow::raw`]); main thread only.
+    pub fn resize(window: *mut c_void, w: f64, h: f64) {
+        // SAFETY: `IsWindow` accepts any value.
+        if !on_main_thread() || window.is_null() || unsafe { IsWindow(window) } == 0 {
+            return;
+        }
+        // SAFETY: a live window of this thread; style values are read, not changed.
+        let (style, ex) = unsafe { (GetWindowLongPtrW(window, GWL_STYLE) as u32, GetWindowLongPtrW(window, GWL_EXSTYLE) as u32) };
+        let (ow, oh) = outer_size(style, ex, w, h);
+        // SAFETY: as above; only the size changes.
+        unsafe { SetWindowPos(window, std::ptr::null_mut(), 0, 0, ow, oh, SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE) };
+    }
+}
+
+/// Other platforms: embedded editors are not hosted (floating ones still are).
+#[cfg(not(windows))]
+mod hostwin {
+    use std::ffi::c_void;
+
+    pub const SUPPORTED: bool = false;
+
+    pub struct HostWindow;
+
+    impl HostWindow {
+        pub fn new(_title: &str, _w: f64, _h: f64) -> Result<HostWindow, String> {
+            Err("embedded plugin editors are not hosted on this platform".into())
+        }
+        pub fn raw(&self) -> *mut c_void {
+            std::ptr::null_mut()
+        }
+        pub fn parent(&self) -> *mut c_void {
+            std::ptr::null_mut()
+        }
+        pub fn raise(&self) {}
+        pub fn is_visible(&self) -> bool {
+            false
+        }
+        pub fn close(self) {}
+    }
+
+    pub fn resize(_window: *mut c_void, _w: f64, _h: f64) {}
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/clap-host/src/lib.rs

@@ -20,8 +20,10 @@
 //! Plugin state (`clap.state`) round-trips through [`Plugin::save_state`] /
 //! [`Plugin::load_state`] as an opaque blob. Plugin editors (`clap.gui`) open as the plugin's own
 //! floating window ([`Plugin::open_editor`], or [`Plugin::editor`] for a handle usable on the main
-//! thread while the instance processes on the audio thread); plugins that offer only embedded
-//! editors are not hosted yet, and SoundCraft's generic parameter editor still works for them.
+//! thread while the instance processes on the audio thread). Plugins that offer only an embedded
+//! editor get a host window of SoundCraft's on Windows (resized on `request_resize`, closed by
+//! its title bar); elsewhere they are not hosted yet, and SoundCraft's generic parameter editor
+//! still works for them.
 //! Parameter changes made in the plugin's GUI arrive as output events while the plugin processes
 //! and are reported by the editor's `idle`.
 

crates/vst3-host/Cargo.toml

@@ -23,6 +23,10 @@ objc2 = "0.6"
 objc2-foundation = { version = "0.3", default-features = false, features = ["std", "NSGeometry", "NSString"] }
 objc2-app-kit = { version = "0.3", default-features = false, features = ["std", "NSApplication", "NSResponder", "NSView", "NSWindow", "NSGraphics"] }
 
+# The Windows editor host window (a top-level HWND the plugin view's child window lives in).
+[target.'cfg(windows)'.dependencies]
+windows-sys = { version = "0.61", features = ["Win32_Foundation", "Win32_Graphics_Gdi", "Win32_System_LibraryLoader", "Win32_UI_Input_KeyboardAndMouse", "Win32_UI_WindowsAndMessaging"] }
+
 [[test]]
 name = "editor_main_thread"
 harness = false

crates/vst3-host/src/ffi.rs

@@ -1928,8 +1928,181 @@ mod window {
     }
 }
 
+/// The Windows host window: a top-level window owned by the app's active window (so it stays
+/// above it and has no taskbar button) whose client area is the plugin view's `HWND` parent.
+/// Closing it only hides it; the editor link notices in `idle`, detaches the view, then destroys
+/// the window. Messages are dispatched by the app's own event loop on the main thread.
+#[cfg(windows)]
+mod window {
+    use std::ffi::{c_char, c_void};
+    use std::sync::OnceLock;
+    use windows_sys::Win32::Foundation::{HWND, LPARAM, LRESULT, RECT, WPARAM};
+    use windows_sys::Win32::System::LibraryLoader::GetModuleHandleW;
+    use windows_sys::Win32::UI::Input::KeyboardAndMouse::GetActiveWindow;
+    use windows_sys::Win32::UI::WindowsAndMessaging::{
+        AdjustWindowRectEx, CS_HREDRAW, CS_VREDRAW, CW_USEDEFAULT, CreateWindowExW, DefWindowProcW, DestroyWindow, GWL_EXSTYLE, GWL_STYLE,
+        GetWindowLongPtrW, IDC_ARROW, IsWindow, IsWindowVisible, LoadCursorW, RegisterClassExW, SW_HIDE, SW_SHOW, SWP_NOACTIVATE, SWP_NOMOVE,
+        SWP_NOZORDER, SetForegroundWindow, SetWindowPos, ShowWindow, WM_CLOSE, WNDCLASSEXW, WS_CAPTION, WS_CLIPCHILDREN, WS_OVERLAPPED, WS_SYSMENU,
+    };
+
+    pub const PLATFORM_TYPE: Option<*const c_char> = Some(vst3::Steinberg::kPlatformTypeHWND);
+
+    /// Rust names the process's first thread "main"; the app runs its UI (and message loop) there.
+    pub fn on_main_thread() -> bool {
+        std::thread::current().name() == Some("main")
+    }
+
+    fn wide(s: &str) -> Vec<u16> {
+        s.encode_utf16().filter(|&c| c != 0).chain(Some(0)).collect()
+    }
+
+    const STYLE: u32 = WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_CLIPCHILDREN;
+
+    unsafe extern "system" fn wndproc(hwnd: HWND, msg: u32, wparam: WPARAM, lparam: LPARAM) -> LRESULT {
+        if msg == WM_CLOSE {
+            // SAFETY: `hwnd` is the window this procedure was called for.
+            unsafe { ShowWindow(hwnd, SW_HIDE) };
+            return 0;
+        }
+        // SAFETY: default handling of a message for the window it was sent to.
+        unsafe { DefWindowProcW(hwnd, msg, wparam, lparam) }
+    }
+
+    /// Registers the window class once; the name lives for the whole process.
+    fn class_name() -> Option<&'static [u16]> {
+        static CLASS: OnceLock<Option<Vec<u16>>> = OnceLock::new();
+        CLASS
+            .get_or_init(|| {
+                let name = wide("SoundCraftVst3Editor");
+                // SAFETY: null asks for this process's module handle.
+                let instance = unsafe { GetModuleHandleW(std::ptr::null()) };
+                let wc = WNDCLASSEXW {
+                    cbSize: std::mem::size_of::<WNDCLASSEXW>() as u32,
+                    style: CS_HREDRAW | CS_VREDRAW,
+                    lpfnWndProc: Some(wndproc),
+                    cbClsExtra: 0,
+                    cbWndExtra: 0,
+                    hInstance: instance,
+                    hIcon: std::ptr::null_mut(),
+                    // SAFETY: a system cursor (null instance + predefined id).
+                    hCursor: unsafe { LoadCursorW(std::ptr::null_mut(), IDC_ARROW) },
+                    hbrBackground: std::ptr::null_mut(),
+                    lpszMenuName: std::ptr::null(),
+                    lpszClassName: name.as_ptr(),
+                    hIconSm: std::ptr::null_mut(),
+                };
+                // SAFETY: a fully initialised class description whose strings outlive the call
+                // (the name is kept for the process lifetime in this `OnceLock`).
+                (unsafe { RegisterClassExW(&wc) } != 0).then_some(name)
+            })
+            .as_deref()
+    }
+
+    /// Outer window size for a client area of `w`×`h`.
+    fn outer_size(style: u32, ex_style: u32, w: f64, h: f64) -> (i32, i32) {
+        let mut r = RECT { left: 0, top: 0, right: w as i32, bottom: h as i32 };
+        // SAFETY: `r` is a valid, writable rect.
+        unsafe { AdjustWindowRectEx(&mut r, style, 0, ex_style) };
+        (r.right.saturating_sub(r.left), r.bottom.saturating_sub(r.top))
+    }
+
+    /// Owns the window handle; destroyed in `close` (main thread only).
+    pub struct HostWindow {
+        hwnd: HWND,
+    }
+
+    // SAFETY: the handle is only used on the main thread (every method checks); the struct
+    // merely carries it between threads' locks.
+    unsafe impl Send for HostWindow {}
+
+    impl HostWindow {
+        fn live(&self) -> Option<HWND> {
+            // SAFETY: `IsWindow` accepts any value and only reports whether it names a window.
+            (on_main_thread() && unsafe { IsWindow(self.hwnd) } != 0).then_some(self.hwnd)
+        }
+
+        pub fn new(title: &str, w: f64, h: f64) -> Result<HostWindow, String> {
+            if !on_main_thread() {
+                return Err("not on the main thread".into());
+            }
+            let class = class_name().ok_or_else(|| "cannot register the editor window class".to_string())?;
+            let title = wide(title);
+            let (ow, oh) = outer_size(STYLE, 0, w, h);
+            // SAFETY: main thread; the active window (or null) of this thread's queue.
+            let owner = unsafe { GetActiveWindow() };
+            // SAFETY: registered class and NUL-terminated strings that outlive the call; the
+            // owner is null or a window of this thread.
+            let hwnd = unsafe {
+                CreateWindowExW(
+                    0,
+                    class.as_ptr(),
+                    title.as_ptr(),
+                    STYLE,
+                    CW_USEDEFAULT,
+                    CW_USEDEFAULT,
+                    ow,
+                    oh,
+                    owner,
+                    std::ptr::null_mut(),
+                    GetModuleHandleW(std::ptr::null()),
+                    std::ptr::null(),
+                )
+            };
+            if hwnd.is_null() {
+                return Err("cannot create the editor window".into());
+            }
+            Ok(HostWindow { hwnd })
+        }
+
+        /// The window handle (for the plug frame's resizes).
+        pub fn raw(&self) -> *mut c_void {
+            self.hwnd
+        }
+
+        /// The `HWND` the plugin view creates its child window in.
+        pub fn parent(&self) -> *mut c_void {
+            self.live().unwrap_or(std::ptr::null_mut())
+        }
+
+        pub fn raise(&self) {
+            if let Some(h) = self.live() {
+                // SAFETY: a live window of this thread.
+                unsafe {
+                    ShowWindow(h, SW_SHOW);
+                    SetForegroundWindow(h);
+                }
+            }
+        }
+
+        pub fn is_visible(&self) -> bool {
+            // SAFETY: a live window of this thread.
+            self.live().is_some_and(|h| unsafe { IsWindowVisible(h) } != 0)
+        }
+
+        pub fn close(self) {
+            if let Some(h) = self.live() {
+                // SAFETY: our own live window; the view was detached before (see `teardown`).
+                unsafe { DestroyWindow(h) };
+            }
+        }
+    }
+
+    /// Resizes a host window's client area (`window` from [`HostWindow::raw`]); main thread only.
+    pub fn resize(window: *mut c_void, w: f64, h: f64) {
+        // SAFETY: `IsWindow` accepts any value.
+        if !on_main_thread() || window.is_null() || unsafe { IsWindow(window) } == 0 {
+            return;
+        }
+        // SAFETY: a live window of this thread; style values are read, not changed.
+        let (style, ex) = unsafe { (GetWindowLongPtrW(window, GWL_STYLE) as u32, GetWindowLongPtrW(window, GWL_EXSTYLE) as u32) };
+        let (ow, oh) = outer_size(style, ex, w, h);
+        // SAFETY: as above; only the size changes.
+        unsafe { SetWindowPos(window, std::ptr::null_mut(), 0, 0, ow, oh, SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE) };
+    }
+}
+
 /// Other platforms: no editor windows yet (opening reports "unsupported").
-#[cfg(not(target_os = "macos"))]
+#[cfg(not(any(target_os = "macos", windows)))]
 mod window {
     use std::ffi::{c_char, c_void};
 

crates/vst3-host/src/lib.rs

@@ -25,13 +25,15 @@
 //! component state is accepted too) and re-reads the parameter values.
 //!
 //! Plugin editors (`IPlugView`): on macOS the view is attached to the content `NSView` of a host
-//! `NSWindow` (titled and closable, floating above the app, resized on `IPlugFrame::resizeView`).
+//! `NSWindow` (titled and closable, floating above the app, resized on `IPlugFrame::resizeView`);
+//! on Windows it is attached to a host `HWND` owned by the app's window (no taskbar button,
+//! closing it hides it until the link tears it down).
 //! [`Plugin::open_editor`] opens it directly; [`Plugin::editor`] returns a handle usable on the
 //! main thread while the instance processes on the audio thread (VST3's own threading model:
 //! the controller and its views live on the UI thread). Parameter edits made in the editor
 //! (`IComponentHandler::performEdit`) are reported by the handle's `idle` so the host can write
-//! them into the session. Windows (HWND) and Linux (X11) editor windows are not hosted yet:
-//! opening reports "unsupported".
+//! them into the session. Linux (X11) editor windows are not hosted yet: opening reports
+//! "unsupported".
 //!
 //! Not hosted yet: `IMessage`/`IAttributeList` creation through the host (plugins that need it
 //! for processor ↔ controller messaging may lose those messages), sidechain (aux buses are kept

crates/vst3-host/tests/editor_main_thread.rs

@@ -9,8 +9,8 @@ fn main() {
     let dir = common::fixture_dir();
     let gain = soundcraft_vst3_host::scan_paths(&[dir.to_path_buf()]).into_iter().find(|d| d.name == "Fixture Gain").expect("fixture").id;
     let mut p = soundcraft_vst3_host::instantiate_plugin(&gain).expect("instantiate");
-    // Editor windows are hosted on macOS only; elsewhere the probe reports "unsupported".
-    if cfg!(target_os = "macos") {
+    // Editor windows are hosted on macOS and Windows; elsewhere the probe reports "unsupported".
+    if cfg!(any(target_os = "macos", windows)) {
         assert_eq!(p.editor_size(), Ok((320, 240)));
     } else {
         assert!(p.editor_size().is_err());

crates/vst3-host/tests/fixture_e2e.rs

@@ -271,8 +271,8 @@ fn host_set_controller_param_survives_state_round_trip() {
 fn editor_view_is_probed_and_edits_come_back_as_plain_values() {
     let id = id_of("Fixture Gain");
     let mut p = soundcraft_vst3_host::instantiate_plugin(&id).unwrap();
-    // Editor windows are hosted on macOS only; elsewhere the probe reports "unsupported".
-    if cfg!(target_os = "macos") {
+    // Editor windows are hosted on macOS and Windows; elsewhere the probe reports "unsupported".
+    if cfg!(any(target_os = "macos", windows)) {
         assert_eq!(p.editor_size(), Ok((320, 240)));
     } else {
         assert!(p.editor_size().is_err());
@@ -281,7 +281,7 @@ fn editor_view_is_probed_and_edits_come_back_as_plain_values() {
     // The fixture "edits" Gain to 0.9 (normalized) when it gets the component handler.
     assert_eq!(ed.idle(), vec![("7".to_string(), 1.8)]);
     assert!(ed.idle().is_empty());
-    if cfg!(target_os = "macos") {
+    if cfg!(any(target_os = "macos", windows)) {
         assert!(ed.open().unwrap_err().contains("main thread"), "test threads are not the main thread");
     } else {
         assert!(ed.open().is_err(), "unsupported elsewhere");

docs/plugin-parity.md

@@ -1,6 +1,6 @@
 # Plugin parity: built-in processors and plugin hosting
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-10 · **Change:** major (first plugin checklist against Pro Tools 2026.4.1) · **Target:** Avid Pro Tools Ultimate 2026.4.1
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-10-12 · **Change:** minor (plugin editors on Windows) · **Target:** Avid Pro Tools Ultimate 2026.4.1
 
 Pro Tools users live in plugins: the bundled set covers everyday mixing, and third-party plugins
 cover the rest. This doc tracks both. Our plugins have our own names and are written from
@@ -44,8 +44,8 @@ User report #152: a saved instrument level does not reach the bounce.
 | Notes / MIDI to instruments | ✅ | ✅ | But no live MIDI input (G-02) |
 | State saved in sessions, presets | ✅ | ✅ | |
 | Create/destroy off the audio thread | ✅ | ✅ | |
-| Editors: CLAP | — | 🟡 floating windows; no embedded GUI | |
-| Editors: VST3 | — | 🟡 macOS only (verified with a commercial pitch editor) | Windows/Linux views missing |
+| Editors: CLAP | — | 🟡 floating windows; embedded editors on Windows | Embedded on macOS/Linux missing |
+| Editors: VST3 | — | 🟡 macOS (verified with a commercial pitch editor) and Windows (verified with a free JUCE compressor) | Linux views missing |
 | Editors: AU | — | ❌ | Cocoa view hosting missing |
 | Multiple editor pages | ✅ | 🟡 | #6 |
 | macOS hardened-runtime entitlement for third-party code | ✅ | ❌ | #153, #149 — signed builds refuse third-party VST3 |
@@ -58,4 +58,5 @@ User report #152: a saved instrument level does not reach the bounce.
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-12 | minor | Editors: VST3 and embedded CLAP editors on Windows |
 | 2026-10-10 | major | Created: built-in processor inventory by category and third-party hosting checklist |