fix(komorebi): account for border decorations on resize

The SetWindowPos API will inset the provided dimensions by the amount of
space required for window decorations (shadows, etc). Compute the size
of the decorations and add them as padding to the provided size,
resulting in windows being set precisely to the target dimensions.

An active_window_border_width=1, active_window_border_offset=-1 will now
paint over the 1px window decoration consistently.

The border window is always made topmost on resize, so that it paints
over custom borders (e.g. EPIC Games Launcher) as those borders are
opaque and as such a 1px border configuration as above becomes invisible
in that condition.

komorebi/src/windows_api.rs

@@ -103,7 +103,6 @@ use windows::Win32::UI::WindowsAndMessaging::GWL_EXSTYLE;
 use windows::Win32::UI::WindowsAndMessaging::GWL_STYLE;
 use windows::Win32::UI::WindowsAndMessaging::GW_HWNDNEXT;
 use windows::Win32::UI::WindowsAndMessaging::HWND_BOTTOM;
-use windows::Win32::UI::WindowsAndMessaging::HWND_NOTOPMOST;
 use windows::Win32::UI::WindowsAndMessaging::HWND_TOPMOST;
 use windows::Win32::UI::WindowsAndMessaging::LWA_ALPHA;
 use windows::Win32::UI::WindowsAndMessaging::LWA_COLORKEY;
@@ -342,14 +341,25 @@ impl WindowsApi {
         unsafe { MonitorFromPoint(point, MONITOR_DEFAULTTONEAREST) }.0
     }
 
+    /// position window resizes the target window to the given layout, adjusting
+    /// the layout to account for any window shadow borders (the window painted
+    /// region will match layout on completion).
     pub fn position_window(hwnd: HWND, layout: &Rect, top: bool) -> Result<()> {
         let flags = SetWindowPosition::NO_ACTIVATE
             | SetWindowPosition::NO_SEND_CHANGING
             | SetWindowPosition::NO_COPY_BITS
             | SetWindowPosition::FRAME_CHANGED;
 
+        let shadow_rect = Self::shadow_rect(hwnd)?;
+        let rect = Rect{
+            left: layout.left + shadow_rect.left,
+            top: layout.top + shadow_rect.top,
+            right: layout.right + shadow_rect.right,
+            bottom: layout.bottom + shadow_rect.bottom,
+        };
+
         let position = if top { HWND_TOPMOST } else { HWND_BOTTOM };
-        Self::set_window_pos(hwnd, layout, position, flags.bits())
+        Self::set_window_pos(hwnd, &rect, position, flags.bits())
     }
 
     pub fn bring_window_to_top(hwnd: HWND) -> Result<()> {
@@ -370,7 +380,12 @@ impl WindowsApi {
             SetWindowPosition::NO_ACTIVATE
         };
 
-        let position = HWND_NOTOPMOST;
+        // Always raise the border window to topmost, so that when it is a
+        // single-pixel inset border, it always draws atop the window (i.e.
+        // support an offset of -1 that draws over the Windows 11 default
+        // translucent single pixel border, while reamining visible in cases
+        // such as the EPIC Games launcher that uses an opaque custom border).
+        let position = HWND_TOPMOST;
         Self::set_window_pos(hwnd, layout, position, flags.bits())
     }
 
@@ -381,7 +396,8 @@ impl WindowsApi {
         Self::set_window_pos(hwnd, &Rect::default(), position, flags.bits())
     }
 
-    pub fn set_window_pos(hwnd: HWND, layout: &Rect, position: HWND, flags: u32) -> Result<()> {
+    /// set_window_pos calls SetWindowPos without any accounting for Window decorations.
+    fn set_window_pos(hwnd: HWND, layout: &Rect, position: HWND, flags: u32) -> Result<()> {
         unsafe {
             SetWindowPos(
                 hwnd,
@@ -484,6 +500,25 @@ impl WindowsApi {
         }
     }
 
+    /// shadow_rect computes the offset of the shadow position of the window to
+    /// the window painted region. The four values in the returned Rect can be
+    /// added to a position rect to compute a size for set_window_pos that will
+    /// fill the target area, ignoring shadows.
+    fn shadow_rect(hwnd: HWND) -> Result<Rect> {
+        let window_rect = Self::window_rect(hwnd)?;
+
+        let mut srect = Default::default();
+        unsafe { GetWindowRect(hwnd, &mut srect) }.process()?;
+        let shadow_rect = Rect::from(srect);
+
+        Ok(Rect {
+            left: shadow_rect.left - window_rect.left,
+            top: shadow_rect.top - window_rect.top,
+            right: shadow_rect.right - window_rect.right,
+            bottom: shadow_rect.bottom - window_rect.bottom,
+        })
+    }
+
     fn set_cursor_pos(x: i32, y: i32) -> Result<()> {
         unsafe { SetCursorPos(x, y) }.process()
     }