Reorganize top-level directories with clearer naming convention

app -> app-desktop-macos, presets -> app-presets, server -> remote-server,
daw-config-reaper -> osc-config-daw, plugin-reaper-realearn -> plugin-reaper-relearn.
Updated run.py and presets.py path references accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugin-reaper-relearn/swell-ui/src/brush.rs

@@ -0,0 +1,60 @@
+use base::hash_util::NonCryptoHashMap;
+use reaper_common_types::RgbColor;
+use reaper_low::Swell;
+use reaper_medium::Hbrush;
+use std::cell::RefCell;
+
+#[derive(Debug, Default)]
+pub struct BrushCache {
+    brushes: RefCell<NonCryptoHashMap<BrushDescriptor, Option<Brush>>>,
+}
+
+impl BrushCache {
+    /// Returns a handle to a cached brush according to the given descriptor.
+    ///
+    /// The returned handle is guaranteed to remain valid because we require a static self.
+    pub fn get_brush(&'static self, descriptor: BrushDescriptor) -> Option<Hbrush> {
+        let mut brushes = self.brushes.borrow_mut();
+        brushes
+            .entry(descriptor)
+            .or_insert_with(|| Brush::from_descriptor(descriptor))
+            .as_ref()
+            // It's okay to do this here because we require self to be 'static
+            .map(|brush| brush.to_inner())
+    }
+}
+
+#[derive(Eq, PartialEq, Copy, Clone, Hash, Debug)]
+pub struct BrushDescriptor {
+    color: RgbColor,
+}
+
+impl BrushDescriptor {
+    pub const fn solid(color: RgbColor) -> Self {
+        Self { color }
+    }
+}
+
+/// Owned brush.
+#[derive(Debug)]
+pub struct Brush(Hbrush);
+
+impl Brush {
+    pub fn from_descriptor(desc: BrushDescriptor) -> Option<Self> {
+        let swell_rgb = Swell::RGB(desc.color.r, desc.color.g, desc.color.b);
+        let brush = Swell::get().CreateSolidBrush(swell_rgb as _);
+        Hbrush::new(brush).map(Self)
+    }
+
+    pub fn to_inner(&self) -> Hbrush {
+        self.0
+    }
+}
+
+impl Drop for Brush {
+    fn drop(&mut self) {
+        unsafe {
+            Swell::get().DeleteObject(self.0.as_ptr());
+        }
+    }
+}

plugin-reaper-relearn/swell-ui/src/color.rs

@@ -0,0 +1,13 @@
+use reaper_common_types::RgbColor;
+use reaper_low::Swell;
+
+pub trait SwellRgbColorExt {
+    /// Converts this color to a single integer as expected by Win32/SWELL.
+    fn to_raw(&self) -> u32;
+}
+
+impl SwellRgbColorExt for RgbColor {
+    fn to_raw(&self) -> u32 {
+        Swell::RGB(self.r, self.g, self.b)
+    }
+}

plugin-reaper-relearn/swell-ui/src/device_context.rs

@@ -0,0 +1,30 @@
+use crate::SwellRgbColorExt;
+use reaper_common_types::RgbColor;
+use reaper_low::{raw, Swell};
+use reaper_medium::Hdc;
+
+/// Represents a device context (HDC).
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct DeviceContext(Hdc);
+
+impl DeviceContext {
+    pub fn new(hdc: Hdc) -> DeviceContext {
+        Self(hdc)
+    }
+
+    pub fn as_ptr(&self) -> raw::HDC {
+        self.0.as_ptr()
+    }
+
+    pub fn set_bk_mode_to_transparent(&self) {
+        unsafe {
+            Swell::get().SetBkMode(self.as_ptr(), raw::TRANSPARENT as _);
+        }
+    }
+
+    pub fn set_text_color(&self, color: RgbColor) {
+        unsafe {
+            Swell::get().SetTextColor(self.as_ptr(), color.to_raw() as _);
+        }
+    }
+}

plugin-reaper-relearn/swell-ui/src/font.rs

@@ -0,0 +1,66 @@
+use base::hash_util::NonCryptoHashMap;
+use reaper_low::{raw, Swell};
+use reaper_medium::Hfont;
+use std::cell::RefCell;
+
+#[derive(Debug, Default)]
+pub struct FontCache {
+    fonts: RefCell<NonCryptoHashMap<FontDescriptor, Option<Font>>>,
+}
+
+impl FontCache {
+    /// Returns a handle to a cached font according to the given descriptor.
+    ///
+    /// The returned handle is guaranteed to remain valid because we require a static self.
+    pub fn get_font(&'static self, descriptor: FontDescriptor) -> Option<Hfont> {
+        let mut fonts = self.fonts.borrow_mut();
+        fonts
+            .entry(descriptor)
+            .or_insert_with(|| Font::from_descriptor(descriptor))
+            .as_ref()
+            // It's okay to do this here because we require self to be 'static
+            .map(|font| font.to_inner())
+    }
+}
+
+#[derive(Eq, PartialEq, Copy, Clone, Hash, Debug)]
+pub struct FontDescriptor {
+    pub name: &'static str,
+    pub size: u32,
+}
+
+impl FontDescriptor {
+    pub const fn new(name: &'static str, size: u32) -> Self {
+        Self { name, size }
+    }
+}
+
+/// Owned font.
+#[derive(Debug)]
+pub struct Font(Hfont);
+
+impl Font {
+    pub fn from_descriptor(desc: FontDescriptor) -> Option<Self> {
+        let mut font = raw::LOGFONT {
+            lfHeight: desc.size as _,
+            ..Default::default()
+        };
+        for (i, byte) in desc.name.bytes().take(31).enumerate() {
+            font.lfFaceName[i] = byte as _;
+        }
+        let font = unsafe { Swell::get().CreateFontIndirect(&mut font as *mut _) };
+        Hfont::new(font).map(Self)
+    }
+
+    pub fn to_inner(&self) -> Hfont {
+        self.0
+    }
+}
+
+impl Drop for Font {
+    fn drop(&mut self) {
+        unsafe {
+            Swell::get().DeleteObject(self.0.as_ptr());
+        }
+    }
+}

plugin-reaper-relearn/swell-ui/src/lib.rs

@@ -0,0 +1,41 @@
+mod view_manager;
+pub use view_manager::*;
+
+mod window;
+pub use window::*;
+
+mod device_context;
+pub use device_context::*;
+
+mod menu;
+pub use menu::*;
+
+mod view;
+pub use view::*;
+
+mod units;
+pub use units::*;
+
+mod types;
+pub use types::*;
+
+mod string_types;
+pub use string_types::*;
+
+pub mod menu_tree;
+
+#[macro_use]
+mod color;
+pub use color::*;
+
+mod brush;
+pub use brush::*;
+
+mod font;
+pub use font::*;
+
+#[cfg(target_os = "macos")]
+mod macos;
+
+#[cfg(target_os = "windows")]
+mod win;

plugin-reaper-relearn/swell-ui/src/macos.rs

@@ -0,0 +1,118 @@
+use objc2::foundation::{MainThreadMarker, NSObject};
+use objc2::rc::{Id, Shared};
+use objc2::runtime::Class;
+use objc2::{extern_class, extern_methods, msg_send, msg_send_id, ClassType};
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSApplication;
+
+    unsafe impl ClassType for NSApplication {
+        #[inherits(NSObject)]
+        type Super = NSResponder;
+    }
+);
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSResponder;
+
+    unsafe impl ClassType for NSResponder {
+        type Super = NSObject;
+    }
+);
+
+pub(crate) fn ns_app() -> Id<NSApplication, Shared> {
+    NSApplication::shared(unsafe { MainThreadMarker::new_unchecked() })
+}
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSEvent;
+
+    unsafe impl ClassType for NSEvent {
+        type Super = NSObject;
+    }
+);
+
+extern_methods!(
+    unsafe impl NSApplication {
+        /// This can only be called on the main thread since it may initialize
+        /// the application and since it's parameters may be changed by the main
+        /// thread at any time (hence it is only safe to access on the main thread).
+        pub fn shared(_mtm: MainThreadMarker) -> Id<Self, Shared> {
+            let app: Option<_> = unsafe { msg_send_id![Self::class(), sharedApplication] };
+            // SAFETY: `sharedApplication` always initializes the app if it isn't already
+            unsafe { app.unwrap_unchecked() }
+        }
+
+        pub fn current_event(&self) -> Option<Id<NSEvent, Shared>> {
+            unsafe { msg_send_id![self, currentEvent] }
+        }
+    }
+);
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSWindow;
+
+    unsafe impl ClassType for NSWindow {
+        #[inherits(NSObject)]
+        type Super = NSResponder;
+    }
+);
+
+extern_methods!(
+    unsafe impl NSWindow {
+        #[sel(sendEvent:)]
+        pub unsafe fn send_event(&self, event: &NSEvent);
+
+        pub fn content_view(&self) -> Option<Id<NSView, Shared>> {
+            unsafe { msg_send_id![self, contentView] }
+        }
+
+        pub fn child_windows(&self) -> Id<NSArrayOfWindows, Shared> {
+            unsafe { msg_send_id![self, childWindows] }
+        }
+    }
+);
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSView;
+
+    unsafe impl ClassType for NSView {
+        #[inherits(NSObject)]
+        type Super = NSResponder;
+    }
+);
+
+extern_methods!(
+    unsafe impl NSView {
+        pub fn is_kind_of_class(&self, class: &Class) -> bool {
+            unsafe { msg_send![self, isKindOfClass: class] }
+        }
+
+        pub fn window(&self) -> Option<Id<NSWindow, Shared>> {
+            unsafe { msg_send_id![self, window] }
+        }
+    }
+);
+
+extern_class!(
+    #[derive(Debug, PartialEq, Eq, Hash)]
+    pub(crate) struct NSArrayOfWindows;
+
+    unsafe impl ClassType for NSArrayOfWindows {
+        #[inherits(NSObject)]
+        type Super = NSResponder;
+    }
+);
+
+extern_methods!(
+    unsafe impl NSArrayOfWindows {
+        pub fn first_object(&self) -> Option<Id<NSWindow, Shared>> {
+            unsafe { msg_send_id![self, firstObject] }
+        }
+    }
+);

plugin-reaper-relearn/swell-ui/src/menu.rs

@@ -0,0 +1,164 @@
+use crate::SwellStringArg;
+use reaper_low::{raw, Swell};
+
+/// Represents a top-level menu bar with resource management.
+#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct MenuBar {
+    raw: raw::HMENU,
+}
+
+impl MenuBar {
+    pub fn new_popup_menu() -> MenuBar {
+        Self {
+            raw: Swell::get().CreatePopupMenu(),
+        }
+    }
+
+    pub fn load(resource_id: u32) -> Result<MenuBar, &'static str> {
+        let swell = Swell::get();
+        let raw = unsafe {
+            swell.LoadMenu(
+                swell.plugin_context().h_instance(),
+                resource_id as u16 as raw::ULONG_PTR as raw::LPSTR,
+            )
+        };
+        if raw.is_null() {
+            return Err("couldn't load menu");
+        }
+        Ok(MenuBar { raw })
+    }
+
+    pub fn menu(&self) -> Menu {
+        Menu::new(self.raw)
+    }
+
+    pub fn get_sub_menu(&self, index: u32) -> Option<Menu> {
+        get_sub_menu_at(self.raw, index)
+    }
+}
+
+impl Drop for MenuBar {
+    fn drop(&mut self) {
+        unsafe {
+            Swell::get().DestroyMenu(self.raw);
+        }
+    }
+}
+
+/// Represents a menu or submenu.
+///
+/// Doesn't need to implement Drop because Windows will destroy all sub menus automatically
+/// when the root menu is destroyed.
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct Menu {
+    raw: raw::HMENU,
+}
+
+impl Menu {
+    pub fn new(raw: raw::HMENU) -> Self {
+        Self { raw }
+    }
+
+    pub fn raw(self) -> raw::HMENU {
+        self.raw
+    }
+
+    pub fn set_item_checked(self, item_id: u32, checked: bool) {
+        unsafe {
+            Swell::get().CheckMenuItem(
+                self.raw,
+                item_id as _,
+                if checked {
+                    raw::MF_CHECKED
+                } else {
+                    raw::MF_UNCHECKED
+                } as _,
+            );
+        }
+    }
+
+    pub fn add_item<'b>(self, item_id: u32, text: impl Into<SwellStringArg<'b>>) {
+        unsafe {
+            let swell_string_arg = text.into();
+            let mut mi = raw::MENUITEMINFO {
+                fMask: raw::MIIM_TYPE | raw::MIIM_DATA | raw::MIIM_ID,
+                wID: item_id,
+                dwTypeData: swell_string_arg.as_ptr() as _,
+                ..Default::default()
+            };
+            Swell::get().InsertMenuItem(self.raw, -1, 1, &mut mi as _);
+        }
+    }
+
+    pub fn entry_count(&self) -> Result<u32, &'static str> {
+        let res = unsafe { Swell::get().GetMenuItemCount(self.raw) };
+        if res == -1 {
+            return Err("couldn't menu get entry count");
+        }
+        Ok(res as u32)
+    }
+
+    pub fn add_menu<'b>(self, text: impl Into<SwellStringArg<'b>>) -> Menu {
+        unsafe {
+            let swell_string_arg = text.into();
+            let sub_menu = Swell::get().CreatePopupMenu();
+            let mut mi = raw::MENUITEMINFO {
+                fMask: raw::MIIM_TYPE | raw::MIIM_DATA | raw::MIIM_SUBMENU,
+                hSubMenu: sub_menu,
+                dwTypeData: swell_string_arg.as_ptr() as _,
+                ..Default::default()
+            };
+            Swell::get().InsertMenuItem(self.raw, -1, 1, &mut mi as _);
+            Menu::new(sub_menu)
+        }
+    }
+
+    pub fn add_separator(self) {
+        unsafe {
+            let mut mi = raw::MENUITEMINFO {
+                fMask: raw::MIIM_TYPE,
+                fType: raw::MF_SEPARATOR,
+                ..Default::default()
+            };
+            Swell::get().InsertMenuItem(self.raw, -1, 1, &mut mi as _);
+        }
+    }
+
+    pub fn get_sub_menu_at(&self, index: u32) -> Option<Menu> {
+        get_sub_menu_at(self.raw, index)
+    }
+
+    pub fn set_item_text<'b>(self, item_id: u32, text: impl Into<SwellStringArg<'b>>) {
+        unsafe {
+            let swell_string_arg = text.into();
+            let mut mi = raw::MENUITEMINFO {
+                fMask: raw::MIIM_TYPE | raw::MIIM_DATA,
+                dwTypeData: swell_string_arg.as_ptr() as _,
+                ..Default::default()
+            };
+            Swell::get().SetMenuItemInfo(self.raw, item_id as _, 0, &mut mi as _);
+        }
+    }
+
+    pub fn set_item_enabled(self, item_id: u32, enabled: bool) {
+        unsafe {
+            Swell::get().EnableMenuItem(
+                self.raw,
+                item_id as _,
+                if enabled {
+                    raw::MF_ENABLED
+                } else {
+                    raw::MF_GRAYED
+                } as _,
+            );
+        }
+    }
+}
+
+fn get_sub_menu_at(raw: raw::HMENU, index: u32) -> Option<Menu> {
+    let menu = unsafe { Swell::get().GetSubMenu(raw, index as _) };
+    if menu.is_null() {
+        return None;
+    }
+    Some(Menu::new(menu))
+}

plugin-reaper-relearn/swell-ui/src/menu_tree/input.rs

@@ -0,0 +1,184 @@
+use std::fmt::Debug;
+
+#[derive(Debug)]
+pub enum Entry<R> {
+    Menu(Menu<R>),
+    Item(Item<R>),
+    Separator(Separator),
+    Nothing,
+}
+
+impl<R> Entry<R> {
+    fn index_recursive(&mut self, counter: &mut Counter) {
+        match self {
+            Entry::Menu(m) => {
+                m.id = counter.next_value();
+                for e in &mut m.entries {
+                    e.index_recursive(counter);
+                }
+            }
+            Entry::Item(i) => {
+                i.id = counter.next_value();
+            }
+            Entry::Separator(i) => {
+                i.id = counter.next_value();
+            }
+            _ => {}
+        }
+    }
+
+    fn find_item_by_id_recursive(self, id: u32) -> Option<Item<R>> {
+        match self {
+            Entry::Menu(m) => m
+                .entries
+                .into_iter()
+                .find_map(|e| e.find_item_by_id_recursive(id)),
+            Entry::Item(i) => {
+                if i.id == id {
+                    Some(i)
+                } else {
+                    None
+                }
+            }
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Menu<R> {
+    pub id: u32,
+    pub text: String,
+    pub entries: Vec<Entry<R>>,
+}
+
+impl<R> Menu<R> {
+    /// Assigns all menu entries consecutive IDs starting from the given first ID.
+    ///
+    /// Returns next non-used value.
+    ///
+    /// This is useful for popup menus.
+    pub fn index(&mut self, first_id: u32) -> u32 {
+        let mut counter = Counter::starting_from(first_id);
+        for e in &mut self.entries {
+            e.index_recursive(&mut counter);
+        }
+        counter.next_value()
+    }
+
+    /// Returns the item that has the given ID.
+    ///
+    /// Also looks into sub menus.
+    ///
+    /// This is useful for popup menus.
+    pub fn find_item_by_id(self, id: u32) -> Option<Item<R>> {
+        self.entries
+            .into_iter()
+            .find_map(|e| e.find_item_by_id_recursive(id))
+    }
+}
+
+#[derive(Debug)]
+pub struct Item<R> {
+    pub id: u32,
+    pub text: String,
+    pub result: R,
+    pub opts: ItemOpts,
+}
+
+#[derive(Debug)]
+pub struct Separator {
+    pub id: u32,
+    pub text: Option<String>,
+}
+
+/// Unlabeled menu.
+///
+/// This is useful for aggregating a set of entries that can then be added in one go.
+pub fn anonymous_menu<R>(entries: Vec<Entry<R>>) -> Menu<R> {
+    Menu {
+        id: 0,
+        text: "".to_owned(),
+        entries,
+    }
+}
+
+pub fn menu<R>(text: impl Into<String>, entries: Vec<Entry<R>>) -> Entry<R> {
+    Entry::Menu(Menu {
+        id: 0,
+        text: text.into(),
+        entries,
+    })
+}
+
+pub fn item<R>(text: impl Into<String>, result: R) -> Entry<R> {
+    Entry::Item(Item {
+        id: 0,
+        text: text.into(),
+        result,
+        opts: Default::default(),
+    })
+}
+
+pub fn separator<R>() -> Entry<R> {
+    Entry::Separator(Separator { id: 0, text: None })
+}
+
+pub fn labeled_separator<R>(name: impl Into<String>) -> Entry<R> {
+    Entry::Separator(Separator {
+        id: 0,
+        text: Some(name.into()),
+    })
+}
+
+pub fn item_with_opts<R>(text: impl Into<String>, opts: ItemOpts, result: R) -> Entry<R> {
+    Entry::Item(Item {
+        id: 0,
+        text: text.into(),
+        result,
+        opts,
+    })
+}
+
+#[allow(clippy::redundant_closure)]
+pub fn disabled_item<R: Default>(text: impl Into<String>) -> Entry<R> {
+    item_with_opts(
+        text,
+        ItemOpts {
+            enabled: false,
+            checked: false,
+        },
+        R::default(),
+    )
+}
+
+#[derive(Debug)]
+pub struct ItemOpts {
+    pub enabled: bool,
+    pub checked: bool,
+}
+
+impl Default for ItemOpts {
+    fn default() -> Self {
+        Self {
+            enabled: true,
+            checked: false,
+        }
+    }
+}
+
+struct Counter {
+    value: u32,
+}
+
+impl Counter {
+    pub fn starting_from(value: u32) -> Self {
+        Self { value }
+    }
+
+    pub fn next_value(&mut self) -> u32 {
+        let val = self.value;
+        self.value += 1;
+        val
+    }
+}

plugin-reaper-relearn/swell-ui/src/menu_tree/mod.rs

@@ -0,0 +1,5 @@
+mod input;
+pub use input::*;
+
+mod output;
+pub use output::*;

plugin-reaper-relearn/swell-ui/src/menu_tree/output.rs

@@ -0,0 +1,46 @@
+use crate::menu_tree::{Entry, Menu};
+use crate::Menu as SwellMenu;
+
+/// Adds all entries within the given pure menu to the given SWELL menu, ignoring the label of the pure menu.
+///
+/// Also adds a separator first if the SWELL menu already contains entries.
+pub fn add_all_entries_of_menu<R>(swell_menu: SwellMenu, root_menu: &Menu<R>) {
+    // Add separator if there are entries already
+    if swell_menu.entry_count().is_ok_and(|count| count > 0) {
+        swell_menu.add_separator();
+    }
+    // Add entries
+    for e in &root_menu.entries {
+        fill_menu_recursively(swell_menu, e);
+    }
+}
+
+/// Adds the given menu entry and potential sub entries to the given SWELL menu.
+fn fill_menu_recursively<R>(swell_menu: SwellMenu, entry: &Entry<R>) {
+    match entry {
+        Entry::Menu(m) => {
+            let sub_menu = swell_menu.add_menu(m.text.as_str());
+            for e in &m.entries {
+                fill_menu_recursively(sub_menu, e);
+            }
+        }
+        Entry::Item(i) => {
+            swell_menu.add_item(i.id, i.text.as_str());
+            if i.opts.checked {
+                swell_menu.set_item_checked(i.id, true);
+            }
+            if !i.opts.enabled {
+                swell_menu.set_item_enabled(i.id, false);
+            }
+        }
+        Entry::Separator(s) => {
+            swell_menu.add_separator();
+            if let Some(text) = &s.text {
+                swell_menu.add_item(s.id, text.as_str());
+                swell_menu.set_item_enabled(s.id, false);
+                swell_menu.add_separator();
+            }
+        }
+        Entry::Nothing => {}
+    }
+}

plugin-reaper-relearn/swell-ui/src/string_types.rs

@@ -0,0 +1,44 @@
+use reaper_low::raw;
+use std::borrow::Cow;
+use std::ffi::{CStr, CString};
+use std::os::raw::c_char;
+
+pub struct SwellStringArg<'a>(Cow<'a, CStr>);
+
+impl SwellStringArg<'_> {
+    pub fn as_ptr(&self) -> *const c_char {
+        self.0.as_ptr()
+    }
+
+    pub(super) fn as_lparam(&self) -> raw::LPARAM {
+        self.0.as_ptr() as _
+    }
+}
+
+impl<'a> From<&'a CStr> for SwellStringArg<'a> {
+    fn from(s: &'a CStr) -> Self {
+        SwellStringArg(s.into())
+    }
+}
+
+impl<'a> From<&'a str> for SwellStringArg<'a> {
+    fn from(s: &'a str) -> Self {
+        // Requires copying
+        SwellStringArg(
+            CString::new(s)
+                .expect("Rust string too exotic for REAPER")
+                .into(),
+        )
+    }
+}
+
+impl From<String> for SwellStringArg<'_> {
+    fn from(s: String) -> Self {
+        // Doesn't require copying because we own the string now
+        SwellStringArg(
+            CString::new(s)
+                .expect("Rust string too exotic for REAPER")
+                .into(),
+        )
+    }
+}

plugin-reaper-relearn/swell-ui/src/types.rs

@@ -0,0 +1,4 @@
+use std::rc::Rc;
+
+pub type SharedView<V> = Rc<V>;
+pub type WeakView<V> = std::rc::Weak<V>;

plugin-reaper-relearn/swell-ui/src/units.rs

@@ -0,0 +1,297 @@
+use reaper_low::raw;
+use reaper_low::raw::RECT;
+use std::ops::{Add, Mul, Sub};
+
+/// An abstract unit used for dialog dimensions, independent of HiDPI and stuff.
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
+pub struct DialogUnits(pub u32);
+
+impl DialogUnits {
+    pub fn get(self) -> u32 {
+        self.0
+    }
+
+    pub fn as_raw(self) -> i32 {
+        self.0 as _
+    }
+
+    pub fn scale(&self, scale: f64) -> Self {
+        DialogUnits((scale * self.0 as f64).round() as _)
+    }
+}
+
+impl Add for DialogUnits {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self {
+        Self(self.0 + rhs.0)
+    }
+}
+
+impl Mul<u32> for DialogUnits {
+    type Output = Self;
+
+    fn mul(self, rhs: u32) -> Self::Output {
+        Self(self.0 * rhs)
+    }
+}
+
+/// Pixels on a screen.
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct Pixels(pub u32);
+
+impl Pixels {
+    pub fn get(self) -> u32 {
+        self.0
+    }
+
+    pub fn as_raw(self) -> i32 {
+        self.0 as _
+    }
+
+    pub fn scale(&self, scale: f64) -> Self {
+        Pixels((scale * self.0 as f64).round() as _)
+    }
+}
+
+impl Mul<f64> for Pixels {
+    type Output = Self;
+
+    fn mul(self, rhs: f64) -> Self::Output {
+        Self((self.0 as f64 * rhs).round() as _)
+    }
+}
+
+impl Sub for Pixels {
+    type Output = Pixels;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Pixels(self.0 - rhs.0)
+    }
+}
+
+impl Add for Pixels {
+    type Output = Pixels;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Pixels(self.0 + rhs.0)
+    }
+}
+
+/// Point in a coordinate system.
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)]
+pub struct Point<T> {
+    pub x: T,
+    pub y: T,
+}
+
+impl<T> Point<T> {
+    pub const fn new(x: T, y: T) -> Self {
+        Self { x, y }
+    }
+}
+
+/// These factors should correspond to those in `dialogs.cpp`.
+fn effective_scale_factors() -> ScaleFactors {
+    #[cfg(target_os = "linux")]
+    {
+        let scaling_256 = reaper_low::Swell::get().SWELL_GetScaling256();
+        let hidpi_factor = scaling_256 as f64 / 256.0;
+        ScaleFactors {
+            main: 1.9 * hidpi_factor,
+            y: 0.92,
+        }
+    }
+    #[cfg(target_os = "macos")]
+    {
+        ScaleFactors { main: 1.6, y: 0.95 }
+    }
+    #[cfg(target_os = "windows")]
+    {
+        ScaleFactors { main: 1.0, y: 1.0 }
+    }
+}
+
+struct ScaleFactors {
+    /// The main scale factor which affects both x and y coordinates.
+    ///
+    /// Corresponds to `SWELL_DLG_SCALE_AUTOGEN` in `dialogs.cpp`.
+    main: f64,
+    /// An additional scale factor which is applied to y coordinates.
+    ///
+    /// Set to 1.0 if you want to use the main factor only.
+    ///
+    /// Corresponds to `SWELL_DLG_SCALE_AUTOGEN_YADJ` in `dialogs.cpp`.
+    y: f64,
+}
+
+impl ScaleFactors {
+    pub fn x_factor(&self) -> f64 {
+        self.main
+    }
+
+    pub fn y_factor(&self) -> f64 {
+        self.main * self.y
+    }
+}
+
+impl Point<DialogUnits> {
+    /// Converts this dialog unit point to pixels.
+    ///
+    /// The Window struct contains a method which can do this including Windows HiDPI information.
+    pub fn in_pixels(&self) -> Point<Pixels> {
+        // TODO-low On Windows this works differently. See original ReaLearn. But on the other hand
+        //  ... this is only for the first short render before the optimal size is calculated.
+        //  So as long as it works, this heuristic is okay.
+        let scale_factors = effective_scale_factors();
+        Point {
+            x: Pixels((scale_factors.x_factor() * self.x.get() as f64) as _),
+            y: Pixels((scale_factors.y_factor() * self.y.get() as f64) as _),
+        }
+    }
+
+    pub fn scale(self, scaling: &DialogScaling) -> Self {
+        Self {
+            x: self.x.scale(scaling.x_scale),
+            y: self.y.scale(scaling.y_scale),
+        }
+    }
+}
+
+impl<T: Copy> Point<T> {
+    pub fn to_dimensions(self) -> Dimensions<T> {
+        Dimensions::new(self.x, self.y)
+    }
+}
+
+impl<T: Copy> From<Dimensions<T>> for Point<T> {
+    fn from(d: Dimensions<T>) -> Self {
+        d.to_point()
+    }
+}
+
+/// Dimensions of a rectangle.
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct Dimensions<T> {
+    pub width: T,
+    pub height: T,
+}
+
+impl<T> Dimensions<T> {
+    pub const fn new(width: T, height: T) -> Self {
+        Self { width, height }
+    }
+}
+
+impl<T: Copy> Dimensions<T> {
+    pub fn to_point(self) -> Point<T> {
+        Point::new(self.width, self.height)
+    }
+}
+
+impl Dimensions<Pixels> {
+    pub fn to_vst(self) -> (i32, i32) {
+        (self.width.get() as _, self.height.get() as _)
+    }
+
+    pub fn scale(self, scaling: DialogScaling) -> Self {
+        Self {
+            width: self.width.scale(scaling.width_scale),
+            height: self.height.scale(scaling.height_scale),
+        }
+    }
+}
+
+impl Dimensions<DialogUnits> {
+    /// Converts the given dialog unit dimensions to pixels.
+    ///
+    /// Doesn't take window-specific HIDPI info into account! Use `Window` for this.
+    pub fn in_pixels(&self) -> Dimensions<Pixels> {
+        self.to_point().in_pixels().to_dimensions()
+    }
+
+    pub fn scale(self, scaling: &DialogScaling) -> Self {
+        Self {
+            width: self.width.scale(scaling.width_scale),
+            height: self.height.scale(scaling.height_scale),
+        }
+    }
+}
+
+impl<T: Copy> From<Point<T>> for Dimensions<T> {
+    fn from(p: Point<T>) -> Self {
+        p.to_dimensions()
+    }
+}
+
+/// This is not the scaling applied by SWELL but the one applied before by us when generating
+/// the RC file. In future we might produce different RC files for different operating systems.
+/// Then this is maybe the only scaling info we need and we can ditch SWELL scaling.
+#[derive(Debug)]
+pub struct DialogScaling {
+    pub x_scale: f64,
+    pub y_scale: f64,
+    pub width_scale: f64,
+    pub height_scale: f64,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct Rect {
+    pub left: i32,
+    pub top: i32,
+    pub width: u32,
+    pub height: u32,
+}
+
+impl Rect {
+    pub fn contains(&self, point: Point<i32>) -> bool {
+        point.x >= self.left
+            && point.y >= self.top
+            && point.x < self.right()
+            && point.y < self.bottom()
+    }
+
+    pub fn right(&self) -> i32 {
+        self.left + self.width as i32
+    }
+
+    pub fn bottom(&self) -> i32 {
+        self.top + self.height as i32
+    }
+
+    // pub fn normalize(&self, parent_height: u32) -> Self {
+    //     #[cfg(target_os = "macos")]
+    //     {
+    //         Self {
+    //             top: parent_height as i32 - self.top,
+    //             ..*self
+    //         }
+    //     }
+    //     #[cfg(not(target_os = "macos"))]
+    //     {
+    //         *self
+    //     }
+    // }
+}
+
+impl From<raw::RECT> for Rect {
+    fn from(value: RECT) -> Self {
+        Self {
+            left: value.left,
+            top: value.top,
+            width: (value.right - value.left).unsigned_abs(),
+            height: (value.bottom - value.top).unsigned_abs(),
+        }
+    }
+}
+
+impl From<Rect> for raw::RECT {
+    fn from(value: Rect) -> Self {
+        Self {
+            left: value.left,
+            top: value.top,
+            right: value.right(),
+            bottom: value.bottom(),
+        }
+    }
+}

plugin-reaper-relearn/swell-ui/src/view.rs

@@ -0,0 +1,368 @@
+use crate::{create_window, DeviceContext, Pixels, Point, SharedView, Window};
+use reaper_low::raw;
+use rxrust::prelude::*;
+
+use reaper_medium::Hbrush;
+use std::cell::{Cell, RefCell};
+use std::fmt::Debug;
+
+/// Represents a displayable logical part of the UI, such as a panel.
+///
+/// Each view has a 1:0..1 relationship to a window. One can say that a view is
+/// implemented/displayed by a window. A window (= HWND) is the more low-level technical
+/// implementation concept which has lots of possible behavior (see `Window` struct) whereas a view
+/// is a higher-level logical concept which uses window methods to implement very particular and
+/// aptly-named logic which makes sense for that part of the UI.
+///
+/// All views have a few things in common, e.g. views can be opened (window gets created) and closed
+/// (window gets destroyed). These common things are modeled by this trait. In addition to a common
+/// interface, this trait provides default implementations for that common behavior.
+///
+/// An other important part of this trait are window events/callbacks, which implementors can
+/// handle.
+///
+/// # Design
+///
+/// ## Why do view callback methods take self not as mutable reference?
+/// win32 window procedures can be *reentered*, see the win32 docs! Now let's assume we would take
+/// self as mutable reference (`&mut self`). If we would have a borrow checker (`RefCell`), it would
+/// complain on reentry by panicking. Rightly so. Without `RefCell` things would get very unsafe and
+/// we wouldn't even get notified about it. I think the only correct way is to never let the window
+/// procedure call view methods in a mutable context. Make all view handler methods take an
+/// immutable reference. The same strategy which we are using with `IReaperControlSurface` in
+/// `reaper-rs`, because this is reentrant as well.
+///
+/// ## Why are there no exceptions?
+/// One could argue that e.g. `WM_INITDIALOG` is not reentered and we could therefore make an
+/// exception. But not only the win32 window procedure might call our view, also our own code. Just
+/// think of a `close()` method which takes `&mut self` and calls `DestroyWindow()`. Windows would
+/// send a `WM_INITDIALOG` message while we are still in the `close()` method, et voilà ... we would
+/// have 2 mutable accesses. It's just not safe and would cause a false feeling of security!
+///
+/// ## So how do we mutate things in the callback methods?
+/// Everything which needs to be mutable needs to be wrapped with a `RefCell`. We need to pursue the
+/// fine-granular `RefCell` approach because reentrancy is unavoidable. We just need to make sure
+/// not to write to the same data member non-exclusively. If we fail to achieve that, at least
+/// the panic lets us know about the issue.
+///
+/// ## Why do view callback methods take self as `SharedView<Self>`?
+/// Given the above mentioned safety measures and knowing that we must keep views as `Rc`s anyway
+/// (for lifetime reasons, see `ViewManager`), it is possible to take self as `SharedView<Self>`
+/// without sacrificing anything. The obvious advantage we have is that it gives us an easy way to
+/// access view methods in subscribe closures without running into lifetime problems (such as &self
+/// disappearing while still being used in the closure).
+pub trait View: Debug {
+    // Data providers (implementation required, used internally)
+    // =========================================================
+
+    /// ID of the dialog resource to look up when creating the window.
+    ///
+    /// The dialog resource basically defines the window's initial look.
+    fn dialog_resource_id(&self) -> u32;
+
+    /// Returns the current window, if any.
+    ///
+    /// In order to implement behavior common to views, the `View` trait needs mutable access to
+    /// this context.
+    fn view_context(&self) -> &ViewContext;
+
+    // Event handlers (implementation optional)
+    // =================================================
+
+    /// WM_INITDIALOG.
+    ///
+    /// Should return `true` if you want the window to be actually shown when it's created.
+    fn show_window_on_init(&self) -> bool {
+        true
+    }
+
+    /// WM_INITDIALOG.
+    ///
+    /// Should return `true` if keyboard focus is desired.
+    fn opened(self: SharedView<Self>, _window: Window) -> bool {
+        false
+    }
+
+    /// WM_CLOSE.
+    ///
+    /// Should return `true` if the window must not be destroyed.
+    fn close_requested(self: SharedView<Self>) -> bool {
+        false
+    }
+
+    /// WM_DESTROY.
+    fn on_destroy(self: SharedView<Self>, _window: Window) {}
+
+    /// WM_SHOWWINDOW.
+    ///
+    /// Should return `true` if processed.
+    fn shown_or_hidden(self: SharedView<Self>, shown: bool) -> bool {
+        let _ = shown;
+        false
+    }
+
+    /// WM_COMMAND, HIWORD(wparam) == 0.
+    fn button_clicked(self: SharedView<Self>, resource_id: u32) {
+        let _ = resource_id;
+    }
+
+    /// WM_COMMAND, HIWORD(wparam) == CBN_SELCHANGE
+    fn option_selected(self: SharedView<Self>, resource_id: u32) {
+        let _ = resource_id;
+    }
+
+    /// WM_VSCROLL, LOWORD(wparam).
+    ///
+    /// Should return `true` if processed.
+    fn scrolled_vertically(self: SharedView<Self>, _code: u32) -> bool {
+        false
+    }
+
+    /// WM_HSCROLL, lparam (!= 0).
+    fn slider_moved(self: SharedView<Self>, _slider: Window) {}
+
+    /// Should return `true` if processed.
+    fn resized(self: SharedView<Self>) -> bool {
+        false
+    }
+
+    /// Should return `true` if processed.
+    fn focused(self: SharedView<Self>) -> bool {
+        false
+    }
+
+    /// WM_MOUSEWHEEL, HIWORD(wparam).
+    ///
+    /// Should return `true` if processed.
+    fn mouse_wheel_turned(self: SharedView<Self>, distance: i32) -> bool {
+        let _ = distance;
+        false
+    }
+
+    /// WM_MOUSEMOVE.
+    ///
+    /// Should return `true` if processed.
+    fn mouse_moved(self: SharedView<Self>, position: Point<i32>) -> bool {
+        let _ = position;
+        false
+    }
+
+    /// WM_NCHITTEST.
+    ///
+    /// Should return `true` if processed.
+    fn mouse_test(self: SharedView<Self>, position: Point<i32>) -> bool {
+        let _ = position;
+        false
+    }
+
+    /// When F1 was pressed.
+    ///
+    /// Should return `true` if processed.
+    fn help_requested(&self) -> bool {
+        false
+    }
+
+    /// WM_KEYDOWN.
+    ///
+    /// Should return `true` if processed.
+    fn key_down(self: SharedView<Self>, key_code: u8) -> bool {
+        let _ = key_code;
+        false
+    }
+
+    /// WM_KEYUP.
+    ///
+    /// On macOS, a multi-line text field fires this instead of edit_control_changed.
+    /// But it's not fired on Windows!
+    ///
+    /// Should return `true` if processed.
+    fn key_up(self: SharedView<Self>, key_code: u8) -> bool {
+        let _ = key_code;
+        false
+    }
+
+    /// EN_CHANGE, LOWORD(wparam).
+    ///
+    /// Should return `true` if processed.
+    fn edit_control_changed(self: SharedView<Self>, resource_id: u32) -> bool {
+        let _ = resource_id;
+        false
+    }
+
+    /// EN_SETFOCUS, LOWORD(wparam).
+    ///
+    /// Should return `true` if processed.
+    fn edit_control_focus_set(self: SharedView<Self>, resource_id: u32) -> bool {
+        let _ = resource_id;
+        false
+    }
+
+    /// EN_KILLFOCUS, LOWORD(wparam).
+    ///
+    /// Should return `true` if processed.
+    ///
+    /// Currently not fired on Linux!
+    fn edit_control_focus_killed(self: SharedView<Self>, _resource_id: u32) -> bool {
+        false
+    }
+
+    /// WM_CONTEXTMENU
+    ///
+    /// Should return `true` if processed in order to prevent the context menu request going up to higher layers.
+    fn context_menu_wanted(self: SharedView<Self>, _location: Point<Pixels>) -> bool {
+        false
+    }
+
+    /// WM_PAINT
+    ///
+    /// Should return `true` if processed.
+    fn paint(self: SharedView<Self>) -> bool {
+        false
+    }
+
+    /// WM_ERASEBKGND
+    ///
+    /// Should return `true` if processed.
+    fn erase_background(self: SharedView<Self>, device_context: DeviceContext) -> bool {
+        let _ = device_context;
+        false
+    }
+
+    /// WM_CTLCOLORSTATIC
+    ///
+    /// Can return a custom background brush for painting that control.
+    fn control_color_static(
+        self: SharedView<Self>,
+        device_context: DeviceContext,
+        window: Window,
+    ) -> Option<Hbrush> {
+        let _ = device_context;
+        let _ = window;
+        None
+    }
+
+    /// WM_CTLCOLORDLG
+    ///
+    /// Can return a custom background brush for painting that dialog.
+    fn control_color_dialog(
+        self: SharedView<Self>,
+        device_context: DeviceContext,
+        window: Window,
+    ) -> Option<Hbrush> {
+        let _ = device_context;
+        let _ = window;
+        None
+    }
+
+    /// Timer with the given ID fires.
+    ///
+    /// Should return `true` if processed.
+    fn timer(&self, id: usize) -> bool {
+        let _ = id;
+        false
+    }
+
+    /// Called whenever the DialogProc (not WindowProc!!!) is called, before any other callback
+    /// method.
+    ///
+    /// Return `None` to indicate that processing should continue, that is, the other callback
+    /// methods should be called accordingly.
+    fn process_raw(
+        &self,
+        window: Window,
+        msg: raw::UINT,
+        wparam: raw::WPARAM,
+        lparam: raw::LPARAM,
+    ) -> Option<raw::INT_PTR> {
+        let _ = window;
+        let _ = msg;
+        let _ = wparam;
+        let _ = lparam;
+        None
+    }
+
+    fn get_keyboard_event_receiver(&self, focused_window: Window) -> Option<Window> {
+        Some(focused_window)
+    }
+
+    /// If `true`, `RealearnAccelerator` will forward raw keyboard events to this window.
+    ///
+    /// - Absolutely necessary for egui containers (so that egui receives keyboard events)
+    /// - For normal dialogs this can be bad (at least on Windows) because tabbing through text fields is not possible
+    ///   anymore (https://github.com/helgoboss/helgobox/issues/1213)
+    fn wants_raw_keyboard_input(&self) -> bool {
+        false
+    }
+
+    // Public methods (intended to be used by consumers)
+    // =================================================
+
+    /// Opens this view in the given parent window.
+    fn open(self: SharedView<Self>, parent_window: Window) -> Option<Window>
+    where
+        Self: Sized + 'static,
+    {
+        let resource_id = self.dialog_resource_id();
+        create_window(self, resource_id, Some(parent_window))
+    }
+
+    /// Opens this view in a free window.
+    fn open_without_parent(self: SharedView<Self>) -> Option<Window>
+    where
+        Self: Sized + 'static,
+    {
+        let resource_id = self.dialog_resource_id();
+        create_window(self, resource_id, None)
+    }
+
+    /// Closes this view.
+    fn close(&self) {
+        if let Some(window) = self.view_context().window.get() {
+            window.destroy();
+        }
+    }
+
+    /// Returns whether this view is currently open.
+    fn is_open(&self) -> bool {
+        self.view_context().window.get().is_some()
+    }
+}
+
+/// Context data of a view.
+///
+/// If Rust traits could provide data in the form of fields, this would be it.
+#[derive(Clone, Default, Debug)]
+pub struct ViewContext {
+    pub(crate) window: Cell<Option<Window>>,
+    pub(crate) closed_subject: RefCell<LocalSubject<'static, (), ()>>,
+}
+
+impl ViewContext {
+    /// Returns the current window associated with this view if this view is open.
+    pub fn window(&self) -> Option<Window> {
+        self.window.get()
+    }
+
+    /// Returns the current window associated with this view.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the window doesn't exist (the view is not open).
+    pub fn require_window(&self) -> Window {
+        self.window().expect("window not found but required")
+    }
+
+    /// Returns the control with the given resource ID.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the window or control doesn't exist.
+    pub fn require_control(&self, resource_id: u32) -> Window {
+        self.require_window().require_control(resource_id)
+    }
+
+    /// Fires when the window is closed.
+    pub fn closed(&self) -> impl LocalObservable<'static, Item = (), Err = ()> + 'static {
+        self.closed_subject.borrow().clone()
+    }
+}

plugin-reaper-relearn/swell-ui/src/view_manager.rs

@@ -0,0 +1,347 @@
+//! This file is supposed to encapsulate most of the (ugly) win32 API glue code
+use crate::{
+    BrushCache, BrushDescriptor, DeviceContext, FontCache, FontDescriptor, Pixels, Point,
+    SharedView, View, WeakView, Window,
+};
+use std::cell::{Cell, RefCell};
+
+use reaper_low::{raw, Swell};
+use rxrust::prelude::*;
+use std::os::raw::c_void;
+use std::panic::catch_unwind;
+use std::ptr::null_mut;
+
+use base::hash_util::NonCryptoHashMap;
+use fragile::Fragile;
+use reaper_common_types::RgbColor;
+use reaper_medium::{Hbrush, Hdc, Hfont, Hwnd};
+use std::sync::OnceLock;
+
+/// Creates a window according to the given dialog resource.
+///
+/// It's added as a child to the given parent window and attached to the specified view.
+///
+/// Internally, this creates a new win32 dialog using the given resource ID. Uses the methods in the
+/// given view for all callbacks.
+pub(crate) fn create_window(
+    view: SharedView<dyn View>,
+    resource_id: u32,
+    parent_window: Option<Window>,
+) -> Option<Window> {
+    let swell = Swell::get();
+    let hwnd = unsafe {
+        // This will call the dialog procedure `view_dialog_proc`. In order to still know which
+        // of the many view objects we are dealing with, we make use of the lparam parameter of
+        // `CreateDialogParamA` by passing it an address which points to the concrete view.
+        // `view_dialog_proc` with message WM_INITDIALOG will be called immediately, not async.
+        // That's important because we must be sure that the given view Rc reference is still
+        // valid when it arrives in `view_dialog_proc`.
+        swell.CreateDialogParam(
+            swell.plugin_context().h_instance(),
+            resource_id as u16 as raw::ULONG_PTR as raw::LPSTR,
+            parent_window.map(|w| w.raw()).unwrap_or(null_mut()),
+            Some(view_dialog_proc),
+            convert_view_ref_to_address(&view),
+        )
+    };
+    Window::new(hwnd)
+}
+
+/// This struct manages the mapping from windows to views.
+///
+/// This is necessary to get from "global" win32 world into beloved "local" Rust struct world.
+#[derive(Default)]
+pub struct ViewManager {
+    /// Holds a mapping from window handles (HWND) to views
+    view_map: RefCell<NonCryptoHashMap<raw::HWND, WeakView<dyn View>>>,
+    brush_cache: BrushCache,
+    font_cache: FontCache,
+}
+
+impl ViewManager {
+    pub fn get_solid_brush(&'static self, color: RgbColor) -> Option<Hbrush> {
+        self.brush_cache.get_brush(BrushDescriptor::solid(color))
+    }
+
+    pub fn get_font(&'static self, descriptor: FontDescriptor) -> Option<Hfont> {
+        self.font_cache.get_font(descriptor)
+    }
+
+    /// If the given window is one of ours (one that drives our views) and the associated view
+    /// still exists, it returns that associated view.
+    pub fn get_associated_view(&self, window: Window) -> Option<SharedView<dyn View>> {
+        let view_map = self.view_map.borrow();
+        let view = view_map.get(&window.raw())?;
+        view.upgrade()
+    }
+
+    /// Returns the global window manager instance
+    pub fn get() -> &'static ViewManager {
+        static VIEW_MANAGER: OnceLock<Fragile<ViewManager>> = OnceLock::new();
+        // We need to initialize the manager lazily because it's impossible to do that using a const
+        // function (at least in Rust stable).
+        VIEW_MANAGER
+            .get_or_init(|| Fragile::new(ViewManager::default()))
+            .get()
+    }
+
+    /// Registers a new HWND-to-view mapping
+    fn register_view(&self, hwnd: raw::HWND, view: &SharedView<dyn View>) {
+        self.view_map
+            .borrow_mut()
+            .insert(hwnd, SharedView::downgrade(view));
+    }
+
+    /// Looks up a view by its corresponding HWND
+    fn lookup_view(&self, hwnd: raw::HWND) -> Option<SharedView<dyn View>> {
+        let view_map = self.view_map.borrow();
+        let weak_view = view_map.get(&hwnd)?;
+        weak_view.upgrade().or_else(|| {
+            // Not existing. The primary owner (most likely a parent view) dropped
+            // it already.
+            tracing::warn!("Requested ui is registered in ui map but has been dropped already");
+            None
+        })
+    }
+
+    /// Unregisters a HWND-to-View mapping
+    fn unregister_view(&self, hwnd: raw::HWND) {
+        self.view_map.borrow_mut().remove(&hwnd);
+    }
+}
+
+// Converts the given view Rc reference to an address which can be transmitted as LPARAM.
+// `SharedView<dyn View>` is a so-called trait object, a *fat* pointer which is twice as large as a
+// normal pointer (on 64-bit architectures 2 x 64 bit = 128 bit = 16 bytes). This is too big to
+// encode within LPARAM. `&SharedView<dyn View>` is *not* a trait object but a reference to the
+// trait object. Therefore it is a thin pointer already.
+fn convert_view_ref_to_address(view_trait_object_ref: &SharedView<dyn View>) -> isize {
+    let view_trait_object_ptr = view_trait_object_ref as *const _ as *const c_void;
+    view_trait_object_ptr as isize
+}
+
+// Converts the given address back to the original view Rc reference.
+fn interpret_address_as_view_ref<'a>(view_trait_object_address: isize) -> &'a SharedView<dyn View> {
+    let view_trait_object_ptr = view_trait_object_address as *const c_void;
+    unsafe { &*(view_trait_object_ptr as *const _) }
+}
+
+/// This is our dialog procedure.
+///
+/// It's called by Windows (or the emulation layer). It basically finds the particular `View`
+/// instance which matches the HWND and then delegates to its methods. Please note that this is
+/// a DialogProc, not a WindowProc. The difference is mainly the return value. A WindowProc
+/// usually returns 0 if the message has been processed, or it delegates to `DefWindowProc()`.
+/// If we do the latter in a DialogProc, non-child windows start to become always modal (not
+/// returning focus) because it's wrong!
+///
+/// In DialogProc it's the opposite: It returns 1 if the message has been processed and 0 if not.
+/// If we have a message where the return value has a special meaning (beyond processed or
+/// unprocesssed), we need to "return" that via `SetWindowLong` instead, except for WM_INITDIALOG.
+/// See https://docs.microsoft.com/en-us/windows/win32/api/winuser/nc-winuser-dlgproc.
+unsafe extern "C" fn view_dialog_proc(
+    hwnd: raw::HWND,
+    msg: raw::UINT,
+    wparam: raw::WPARAM,
+    lparam: raw::LPARAM,
+) -> raw::INT_PTR {
+    catch_unwind(|| {
+        DIALOG_PROC_ALREADY_ENTERED.with(|entered| {
+            // Detect reentrancy
+            let already_entered = entered.replace(true);
+            scopeguard::defer! {
+                if !already_entered {
+                    entered.set(false);
+                }
+            }
+            // Obtain view
+            let view: SharedView<dyn View> = if msg == raw::WM_INITDIALOG {
+                // A view window is initializing. At this point lparam contains the value which we
+                // passed when calling CreateDialogParam. This contains the address of a
+                // view reference. At subsequent calls, this address is not passed anymore
+                // but only the HWND. So we need to save a HWND-to-view mapping now.
+                let view_ref = interpret_address_as_view_ref(lparam as _);
+                ViewManager::get().register_view(hwnd, view_ref);
+                view_ref.clone()
+            } else {
+                // Try to find view corresponding to given HWND
+                match ViewManager::get().lookup_view(hwnd) {
+                    None => {
+                        // View is not (yet) registered. Do default stuff.
+                        return 0;
+                    }
+                    Some(v) => v,
+                }
+            };
+            // Found view.
+            // Delegate to view struct methods.
+            let window = Window::new(hwnd).expect("window was null");
+            if let Some(result) = view.process_raw(window, msg, wparam, lparam) {
+                return result;
+            }
+            const KEYBOARD_MSG_FOR_X_BRIDGE: u32 = raw::WM_USER + 100;
+            match msg {
+                raw::WM_INITDIALOG => {
+                    view.view_context().window.replace(Some(window));
+                    let show_window = view.show_window_on_init();
+                    let keyboard_focus_desired = view.opened(window);
+                    if show_window {
+                        window.show();
+                        // WM_INITDIALOG is special in a DialogProc in that we don't need to use
+                        // `SetWindowLong()` for return values with special meaning.
+                        keyboard_focus_desired.into()
+                    } else {
+                        0
+                    }
+                }
+                raw::WM_SHOWWINDOW => view.shown_or_hidden(wparam == 1).into(),
+                raw::WM_DESTROY => {
+                    let view_context = view.view_context();
+                    view_context.closed_subject.borrow_mut().next(());
+                    view_context.window.replace(None);
+                    view.on_destroy(window);
+                    ViewManager::get().unregister_view(hwnd);
+                    1
+                }
+                // This is called on Linux when receiving a keyboard message via SendMessage.
+                // The only time we do this is when we want to forward keyboard interaction from
+                // the RealearnAccelerator to egui. egui runs in an XBridge window - a sort
+                // of child window of the SWELL window. Returning 0 here makes sure that the
+                // messages are passed through to the XBridge window. This is SWELL functionality
+                // (check the SWELL code).
+                KEYBOARD_MSG_FOR_X_BRIDGE => 0,
+                raw::WM_MOUSEMOVE => view
+                    .mouse_moved(Point::new(
+                        loword_signed(lparam as _),
+                        hiword_signed(lparam as _),
+                    ))
+                    .into(),
+                raw::WM_NCHITTEST => view
+                    .mouse_test(Point::new(
+                        loword_signed(lparam as _),
+                        hiword_signed(lparam as _),
+                    ))
+                    .into(),
+                raw::WM_SIZE => view.resized().into(),
+                raw::WM_SETFOCUS => view.focused().into(),
+                raw::WM_COMMAND => {
+                    let resource_id = loword(wparam as _);
+                    match hiword(wparam as _) as u32 {
+                        0 => {
+                            view.button_clicked(resource_id as _);
+                            // We just say the click is handled. Don't know where this  would not
+                            // be the case.
+                            1
+                        }
+                        raw::CBN_SELCHANGE => {
+                            view.option_selected(resource_id as _);
+                            // We just say the selection is handled. Don't know where this would not
+                            // be the case.
+                            1
+                        }
+                        raw::EN_SETFOCUS => view.edit_control_focus_set(resource_id as _).into(),
+                        raw::EN_KILLFOCUS => {
+                            view.edit_control_focus_killed(resource_id as _).into()
+                        }
+                        raw::EN_CHANGE => {
+                            // Edit control change event is fired even if we change an edit control
+                            // text programmatically. We don't want this. In general.
+                            if already_entered {
+                                return 0;
+                            }
+                            view.edit_control_changed(resource_id as _).into()
+                        }
+                        _ => 0,
+                    }
+                }
+                raw::WM_VSCROLL => {
+                    let code = loword(wparam as _);
+                    view.scrolled_vertically(code as _).into()
+                }
+                raw::WM_HSCROLL => {
+                    if lparam <= 0 {
+                        // This is not a slider. Not interested.
+                        return 0;
+                    }
+                    let raw_slider = Hwnd::new(lparam as raw::HWND).expect("slider hwnd is null");
+                    view.slider_moved(Window::from_hwnd(raw_slider));
+                    1
+                }
+                raw::WM_MOUSEWHEEL => {
+                    let distance = hiword_signed(wparam);
+                    view.mouse_wheel_turned(distance).into()
+                }
+                raw::WM_KEYDOWN => view.key_down(wparam as _).into(),
+                raw::WM_KEYUP => view.key_up(wparam as _).into(),
+                raw::WM_CLOSE => {
+                    let processed = view.close_requested();
+                    if !processed {
+                        window.destroy();
+                    }
+                    1
+                }
+                raw::WM_CONTEXTMENU => {
+                    let x = loword(lparam as _);
+                    let y = hiword(lparam as _);
+                    view.context_menu_wanted(Point::new(Pixels(x as _), Pixels(y as _)))
+                        .into()
+                }
+                raw::WM_PAINT => isize::from(view.paint()),
+                raw::WM_ERASEBKGND => {
+                    if let Some(hdc) = Hdc::new(wparam as raw::HDC) {
+                        isize::from(view.erase_background(DeviceContext::new(hdc)))
+                    } else {
+                        0
+                    }
+                }
+                raw::WM_CTLCOLORSTATIC => {
+                    let brush = view.control_color_static(
+                        DeviceContext::new(
+                            Hdc::new(wparam as raw::HDC).expect("HDC in WM_CTLCOLORSTATIC is null"),
+                        ),
+                        Window::new(lparam as raw::HWND)
+                            .expect("WM_CTLCOLORSTATIC control is null"),
+                    );
+                    brush.map(|b| b.as_ptr()).unwrap_or(null_mut()) as _
+                }
+                raw::WM_CTLCOLORDLG => {
+                    let brush = view.control_color_dialog(
+                        DeviceContext::new(
+                            Hdc::new(wparam as raw::HDC).expect("HDC in WM_CTLCOLORDLG is null"),
+                        ),
+                        Window::new(lparam as raw::HWND).expect("WM_CTLCOLORDLG control is null"),
+                    );
+                    brush.map(|b| b.as_ptr()).unwrap_or(null_mut()) as _
+                }
+                raw::WM_TIMER => {
+                    if view.timer(wparam) {
+                        0
+                    } else {
+                        1
+                    }
+                }
+                _ => 0,
+            }
+        })
+    })
+    .unwrap_or(0)
+}
+
+fn loword(wparam: usize) -> u16 {
+    (wparam & 0xffff) as _
+}
+
+fn loword_signed(wparam: usize) -> i32 {
+    loword(wparam) as i16 as i32
+}
+
+fn hiword(wparam: usize) -> u16 {
+    ((wparam >> 16) & 0xffff) as _
+}
+
+fn hiword_signed(wparam: usize) -> i32 {
+    hiword(wparam) as i16 as i32
+}
+
+// Used for global dialog proc reentrancy check.
+thread_local!(static DIALOG_PROC_ALREADY_ENTERED: Cell<bool> = const { Cell::new(false) });

plugin-reaper-relearn/swell-ui/src/win.rs

@@ -0,0 +1,29 @@
+use libloading::{Library, Symbol};
+use winapi::shared::minwindef::UINT;
+use winapi::shared::windef::HWND;
+
+/// Provides access to some Win32 API functions that are not available in older Windows versions.
+///
+/// This is better than eagerly linking to these functions because then the resulting binary
+/// wouldn't work *at all* in the older Windows versions, whereas with this approach, we can
+/// fall back to alternative logic or alternative values on a case-by-case basis.  
+pub struct DynamicWinApi {
+    user32_library: Library,
+}
+
+impl DynamicWinApi {
+    pub fn load() -> Self {
+        unsafe {
+            Self {
+                user32_library: Library::new("user32.dll").unwrap(),
+            }
+        }
+    }
+
+    /// Should be available from Windows 10 onwards.
+    pub fn get_dpi_for_window(&self) -> Option<Symbol<GetDpiForWindow>> {
+        unsafe { self.user32_library.get(b"GetDpiForWindow\0").ok() }
+    }
+}
+
+type GetDpiForWindow = extern "system" fn(hwnd: HWND) -> UINT;