Refactor, split and fix Win32 resize logic and DPI changes handling

src/win/mod.rs

@@ -1,5 +1,6 @@
 mod drop_target;
 mod keyboard;
+mod win32_window;
 mod window;
 
 pub use window::*;

src/win/win32_window.rs

@@ -0,0 +1,122 @@
+use crate::PhySize;
+use std::convert::TryFrom;
+use std::ffi::OsStr;
+use std::os::windows::ffi::OsStrExt;
+use std::ptr::null_mut;
+use winapi::shared::minwindef::{ATOM, DWORD};
+use winapi::shared::windef::{HWND, RECT};
+use winapi::um::winuser::{
+    AdjustWindowRectEx, CreateWindowExW, GetDpiForWindow, SetWindowPos, SWP_NOACTIVATE, SWP_NOMOVE,
+    SWP_NOZORDER, USER_DEFAULT_SCREEN_DPI, WS_CAPTION, WS_CHILD, WS_CLIPSIBLINGS, WS_MAXIMIZEBOX,
+    WS_MINIMIZEBOX, WS_POPUPWINDOW, WS_SIZEBOX, WS_VISIBLE,
+};
+
+// TODO: handle proper destruction of this window during errors/panics/etc.
+pub(crate) struct Win32Window {
+    pub handle: HWND,
+    style_flags: DWORD,
+}
+
+impl Win32Window {
+    pub fn create(window_class: ATOM, title: &str, size: PhySize, parent: Option<HWND>) -> Self {
+        let mut title: Vec<u16> = OsStr::new(title).encode_wide().collect();
+        title.push(0);
+
+        let style_flags = if parent.is_some() {
+            WS_CHILD | WS_VISIBLE
+        } else {
+            WS_POPUPWINDOW
+                | WS_CAPTION
+                | WS_VISIBLE
+                | WS_SIZEBOX
+                | WS_MINIMIZEBOX
+                | WS_MAXIMIZEBOX
+                | WS_CLIPSIBLINGS
+        };
+
+        let size = client_size_to_window_size(size, style_flags);
+
+        // TODO: handle errors
+        let hwnd = unsafe {
+            CreateWindowExW(
+                0,
+                window_class as _,
+                title.as_ptr(),
+                style_flags,
+                0,
+                0,
+                size.width as i32,
+                size.height as i32,
+                parent.unwrap_or(null_mut()),
+                null_mut(),
+                null_mut(),
+                null_mut(),
+            )
+        };
+
+        Win32Window { style_flags, handle: hwnd }
+    }
+
+    /// Resizes the window.
+    ///
+    /// This *will* immediately trigger a WM_SIZE event.
+    pub fn resize(&self, size: PhySize) {
+        let window_size = client_size_to_window_size(size, self.style_flags);
+
+        unsafe {
+            SetWindowPos(
+                self.handle,
+                null_mut(), // Ignored by SWP_NOZORDER
+                0,          // Ignored by SWP_NOMOVE
+                0,          // Ignored by SWP_NOMOVE
+                window_size.width as i32,
+                window_size.height as i32,
+                SWP_NOZORDER | SWP_NOMOVE,
+            );
+        }
+    }
+
+    /// Sets both the position and size of the window, according to a given raw RECT.
+    ///
+    /// This *will* immediately trigger a WM_SIZE event.
+    pub fn set_raw_pos(&self, rect: &RECT) {
+        unsafe {
+            SetWindowPos(
+                self.handle,
+                null_mut(), // Ignored by SWP_NOZORDER
+                rect.left,
+                rect.top,
+                rect.right.saturating_sub(rect.left),
+                rect.bottom.saturating_sub(rect.top),
+                SWP_NOZORDER | SWP_NOACTIVATE,
+            );
+        }
+    }
+
+    /// Returns current the scale factor of the monitor the window is currently on.
+    pub fn current_scale_factor(&self) -> f64 {
+        // FIXME: Only works on Windows 10.
+        let dpi = unsafe { GetDpiForWindow(self.handle) };
+        dpi as f64 / USER_DEFAULT_SCREEN_DPI as f64
+    }
+}
+
+pub fn client_size_to_window_size(size: PhySize, window_flags: DWORD) -> PhySize {
+    let mut rect = RECT {
+        left: 0,
+        top: 0,
+        // In case the provided size overflows an i32, which would imply it is ridiculously large.
+        right: i32::try_from(size.width).unwrap(),
+        bottom: i32::try_from(size.height).unwrap(),
+    };
+
+    // SAFETY: the provided rect pointer is guaranteed to be valid by the mutable reference.
+    unsafe { AdjustWindowRectEx(&mut rect, window_flags, 0, 0) };
+
+    // These checks are made just in case AdjustWindowRectEx sends back invalid values.
+    // Because this is so unlikely, we can afford to just panic here.
+    let width = rect.right.saturating_sub(rect.left);
+    let height = rect.bottom.saturating_sub(rect.top);
+
+    PhySize { width: u32::try_from(width).unwrap(), height: u32::try_from(height).unwrap() }
+}