From db038d943c336599404d667d52ea879da3cc2ab0 Mon Sep 17 00:00:00 2001
From: moko256 <koutaro.mo@gmail.com>
Date: Thu, 10 Dec 2020 05:16:59 +0900
Subject: [PATCH] On Windows, implement 'Window::set_ime_position' with IMM API

---
 CHANGELOG.md                        |  1 +
 Cargo.toml                          |  1 +
 examples/set_ime_position.rs        | 54 +++++++++++++++++++++++++++++
 src/platform_impl/windows/window.rs | 24 +++++++++++--
 src/window.rs                       |  2 +-
 5 files changed, 78 insertions(+), 4 deletions(-)
 create mode 100644 examples/set_ime_position.rs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d6372d4c..57f574e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Unreleased
 
+- On Windows, implement `Window::set_ime_position`.
 - **Breaking:** On Windows, Renamed `WindowBuilderExtWindows`'s `is_dark_mode` to `theme`.
 - On Windows, add `WindowBuilderExtWindows::with_theme` to set a preferred theme.
 - On Windows, fix bug causing message boxes to appear delayed.
diff --git a/Cargo.toml b/Cargo.toml
index f501f8c1..068b2bc4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -65,6 +65,7 @@ features = [
     "commctrl",
     "dwmapi",
     "errhandlingapi",
+    "imm",
     "hidusage",
     "libloaderapi",
     "objbase",
diff --git a/examples/set_ime_position.rs b/examples/set_ime_position.rs
new file mode 100644
index 00000000..1b2eecc3
--- /dev/null
+++ b/examples/set_ime_position.rs
@@ -0,0 +1,54 @@
+use simple_logger::SimpleLogger;
+use winit::{
+    dpi::PhysicalPosition,
+    event::{ElementState, Event, WindowEvent},
+    event_loop::{ControlFlow, EventLoop},
+    window::WindowBuilder,
+};
+
+fn main() {
+    SimpleLogger::new().init().unwrap();
+    let event_loop = EventLoop::new();
+
+    let window = WindowBuilder::new().build(&event_loop).unwrap();
+    window.set_title("A fantastic window!");
+
+    println!("Ime position will system default");
+    println!("Click to set ime position to cursor's");
+
+    let mut cursor_position = PhysicalPosition::new(0.0, 0.0);
+    event_loop.run(move |event, _, control_flow| {
+        *control_flow = ControlFlow::Wait;
+
+        match event {
+            Event::WindowEvent {
+                event: WindowEvent::CursorMoved { position, .. },
+                ..
+            } => {
+                cursor_position = position;
+            }
+            Event::WindowEvent {
+                event:
+                    WindowEvent::MouseInput {
+                        state: ElementState::Released,
+                        ..
+                    },
+                ..
+            } => {
+                println!(
+                    "Setting ime position to {}, {}",
+                    cursor_position.x, cursor_position.y
+                );
+                window.set_ime_position(cursor_position);
+            }
+            Event::WindowEvent {
+                event: WindowEvent::CloseRequested,
+                ..
+            } => {
+                *control_flow = ControlFlow::Exit;
+                return;
+            }
+            _ => (),
+        }
+    });
+}
diff --git a/src/platform_impl/windows/window.rs b/src/platform_impl/windows/window.rs
index 580fa958..c444863e 100644
--- a/src/platform_impl/windows/window.rs
+++ b/src/platform_impl/windows/window.rs
@@ -18,7 +18,9 @@ use winapi::{
         windef::{HWND, POINT, RECT},
     },
     um::{
-        combaseapi, dwmapi, libloaderapi,
+        combaseapi, dwmapi,
+        imm::{CFS_POINT, COMPOSITIONFORM},
+        libloaderapi,
         objbase::COINIT_APARTMENTTHREADED,
         ole2,
         oleidl::LPDROPTARGET,
@@ -616,9 +618,25 @@ impl Window {
         self.window_state.lock().taskbar_icon = taskbar_icon;
     }
 
+    pub(crate) fn set_ime_position_physical(&self, x: i32, y: i32) {
+        if unsafe { winuser::GetSystemMetrics(winuser::SM_IMMENABLED) } != 0 {
+            let mut composition_form = COMPOSITIONFORM {
+                dwStyle: CFS_POINT,
+                ptCurrentPos: POINT { x, y },
+                rcArea: unsafe { mem::zeroed() },
+            };
+            unsafe {
+                let himc = winapi::um::imm::ImmGetContext(self.window.0);
+                winapi::um::imm::ImmSetCompositionWindow(himc, &mut composition_form);
+                winapi::um::imm::ImmReleaseContext(self.window.0, himc);
+            }
+        }
+    }
+
     #[inline]
-    pub fn set_ime_position(&self, _position: Position) {
-        warn!("`Window::set_ime_position` is ignored on Windows")
+    pub fn set_ime_position(&self, spot: Position) {
+        let (x, y) = spot.to_physical::<i32>(self.scale_factor()).into();
+        self.set_ime_position_physical(x, y);
     }
 
     #[inline]
diff --git a/src/window.rs b/src/window.rs
index 8cf6e066..9ed2de06 100644
--- a/src/window.rs
+++ b/src/window.rs
@@ -677,7 +677,7 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// - **iOS / Android / Web / Windows:** Unsupported.
+    /// - **iOS / Android / Web:** Unsupported.
     #[inline]
     pub fn set_ime_position<P: Into<Position>>(&self, position: P) {
         self.window.set_ime_position(position.into())