Windows: implement resize increments

FEATURES.md

@@ -179,7 +179,7 @@ Legend:
 |Window decorations               |✔️     |✔️     |✔️         |✔️             |**N/A**|**N/A**|**N/A**|✔️      |
 |Window decorations toggle        |✔️     |✔️     |✔️         |✔️             |**N/A**|**N/A**|**N/A**|**N/A** |
 |Window resizing                  |✔️     |✔️     |✔️         |✔️        |**N/A**|**N/A**|✔️        |✔️      |
-|Window resize increments         |❌     |✔️     |✔️         |❌             |**N/A**|**N/A**|**N/A**|**N/A** |
+|Window resize increments         |✔️     |✔️     |✔️         |❌             |**N/A**|**N/A**|**N/A**|**N/A** |
 |Window transparency              |✔️     |✔️     |✔️         |✔️             |**N/A**|**N/A**|N/A        |✔️      |
 |Window blur                      |❌    |❌    |❌        |✔️             |**N/A**|**N/A**|N/A        |❌     |
 |Window maximization              |✔️     |✔️     |✔️         |✔️             |**N/A**|**N/A**|**N/A**|**N/A** |

src/changelog/unreleased.md

@@ -63,6 +63,7 @@ changelog entry.
 - On macOS, add services menu.
 - On Windows, add `with_title_text_color`, and `with_corner_preference` on
   `WindowAttributesExtWindows`.
+- On Windows, implement resize increments.
 
 ### Changed
 
@@ -253,4 +254,4 @@ changelog entry.
 - On Web, fix setting cursor icon overriding cursor visibility.
 - On Windows, fix cursor not confined to center of window when grabbed and hidden.
 - On macOS, fix sequence of mouse events being out of order when dragging on the trackpad.
-- On Wayland, fix decoration glitch on close with some compositors
+- On Wayland, fix decoration glitch on close with some compositors.

src/platform_impl/windows/event_loop.rs

@@ -52,17 +52,19 @@ use windows_sys::Win32::{
             HTCAPTION, HTCLIENT, MINMAXINFO, MNC_CLOSE, MSG, NCCALCSIZE_PARAMS, PM_REMOVE, PT_PEN,
             PT_TOUCH, RI_MOUSE_HWHEEL, RI_MOUSE_WHEEL, SC_MINIMIZE, SC_RESTORE, SIZE_MAXIMIZED,
             SWP_NOACTIVATE, SWP_NOMOVE, SWP_NOSIZE, SWP_NOZORDER, WHEEL_DELTA, WINDOWPOS,
-            WM_CAPTURECHANGED, WM_CLOSE, WM_CREATE, WM_DESTROY, WM_DPICHANGED, WM_ENTERSIZEMOVE,
-            WM_EXITSIZEMOVE, WM_GETMINMAXINFO, WM_IME_COMPOSITION, WM_IME_ENDCOMPOSITION,
-            WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT, WM_INPUT_DEVICE_CHANGE,
-            WM_KEYDOWN, WM_KEYUP, WM_KILLFOCUS, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN,
-            WM_MBUTTONUP, WM_MENUCHAR, WM_MOUSEHWHEEL, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCACTIVATE,
-            WM_NCCALCSIZE, WM_NCCREATE, WM_NCDESTROY, WM_NCLBUTTONDOWN, WM_PAINT, WM_POINTERDOWN,
-            WM_POINTERUP, WM_POINTERUPDATE, WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR,
-            WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE, WM_SYSCOMMAND, WM_SYSKEYDOWN, WM_SYSKEYUP,
-            WM_TOUCH, WM_WINDOWPOSCHANGED, WM_WINDOWPOSCHANGING, WM_XBUTTONDOWN, WM_XBUTTONUP,
-            WNDCLASSEXW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW, WS_EX_TRANSPARENT,
-            WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
+            WMSZ_BOTTOM, WMSZ_BOTTOMLEFT, WMSZ_BOTTOMRIGHT, WMSZ_LEFT, WMSZ_RIGHT, WMSZ_TOP,
+            WMSZ_TOPLEFT, WMSZ_TOPRIGHT, WM_CAPTURECHANGED, WM_CLOSE, WM_CREATE, WM_DESTROY,
+            WM_DPICHANGED, WM_ENTERSIZEMOVE, WM_EXITSIZEMOVE, WM_GETMINMAXINFO, WM_IME_COMPOSITION,
+            WM_IME_ENDCOMPOSITION, WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT,
+            WM_INPUT_DEVICE_CHANGE, WM_KEYDOWN, WM_KEYUP, WM_KILLFOCUS, WM_LBUTTONDOWN,
+            WM_LBUTTONUP, WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MENUCHAR, WM_MOUSEHWHEEL, WM_MOUSEMOVE,
+            WM_MOUSEWHEEL, WM_NCACTIVATE, WM_NCCALCSIZE, WM_NCCREATE, WM_NCDESTROY,
+            WM_NCLBUTTONDOWN, WM_PAINT, WM_POINTERDOWN, WM_POINTERUP, WM_POINTERUPDATE,
+            WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR, WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE,
+            WM_SIZING, WM_SYSCOMMAND, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TOUCH, WM_WINDOWPOSCHANGED,
+            WM_WINDOWPOSCHANGING, WM_XBUTTONDOWN, WM_XBUTTONUP, WNDCLASSEXW, WS_EX_LAYERED,
+            WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW, WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP,
+            WS_VISIBLE,
         },
     },
 };
@@ -1352,6 +1354,98 @@ unsafe fn public_window_callback_inner(
             result = ProcResult::Value(0);
         }
 
+        WM_SIZING => {
+            /// Calculate the amount to add to round `value` to the nearest multiple of `increment`.
+            fn snap_to_nearest_increment_delta(value: i32, increment: i32) -> i32 {
+                let half_one = increment / 2;
+                let half_two = increment - half_one;
+                half_one - (value - half_two) % increment
+            }
+
+            let scale_factor = userdata.window_state_lock().scale_factor;
+            let Some(inc) = userdata
+                .window_state_lock()
+                .resize_increments
+                .map(|inc| inc.to_physical(scale_factor))
+                .filter(|inc| inc.width > 0 && inc.height > 0)
+            else {
+                result = ProcResult::Value(0);
+                return;
+            };
+
+            let side = wparam as u32;
+            // The desired new size of the window, decorations included.
+            let rect = unsafe { &mut *(lparam as *mut RECT) };
+
+            // We need to calculate the dimensions of the window decorations to get the true
+            // size of the window's contents
+            let adj_rect = userdata
+                .window_state_lock()
+                .window_flags
+                .adjust_rect(window, *rect)
+                .unwrap_or(*rect);
+            let deco_width = rect.left - adj_rect.left + adj_rect.right - rect.right;
+            let deco_height = rect.top - adj_rect.top + adj_rect.bottom - rect.bottom;
+
+            let width = rect.right - rect.left - deco_width;
+            let height = rect.bottom - rect.top - deco_height;
+
+            let mut width_delta = snap_to_nearest_increment_delta(width, inc.width);
+            let mut height_delta = snap_to_nearest_increment_delta(height, inc.height);
+
+            // Windows won't bound check the value of `rect` after we're done here, so we
+            // have to check manually. If the width/height we snap to would go out of bounds, just
+            // set it equal to the min/max bound.
+            let min_size = userdata
+                .window_state_lock()
+                .min_size
+                .map(|size| size.to_physical(scale_factor));
+            let max_size = userdata
+                .window_state_lock()
+                .max_size
+                .map(|size| size.to_physical(scale_factor));
+            let final_width = width + width_delta;
+            let final_height = height + height_delta;
+            if let Some(min_size) = min_size {
+                if final_width < min_size.width {
+                    width_delta += min_size.width - final_width;
+                }
+                if final_height < min_size.height {
+                    height_delta += min_size.height - final_height;
+                }
+            }
+            if let Some(max_size) = max_size {
+                if final_width > max_size.width {
+                    width_delta -= final_width - max_size.width;
+                }
+                if final_height > max_size.height {
+                    height_delta -= final_height - max_size.height;
+                }
+            }
+
+            match side {
+                WMSZ_LEFT | WMSZ_BOTTOMLEFT | WMSZ_TOPLEFT => {
+                    rect.left -= width_delta;
+                }
+                WMSZ_RIGHT | WMSZ_BOTTOMRIGHT | WMSZ_TOPRIGHT => {
+                    rect.right += width_delta;
+                }
+                _ => {}
+            }
+
+            match side {
+                WMSZ_TOP | WMSZ_TOPLEFT | WMSZ_TOPRIGHT => {
+                    rect.top -= height_delta;
+                }
+                WMSZ_BOTTOM | WMSZ_BOTTOMLEFT | WMSZ_BOTTOMRIGHT => {
+                    rect.bottom += height_delta;
+                }
+                _ => {}
+            }
+
+            result = ProcResult::DefWindowProc(wparam);
+        }
+
         WM_MENUCHAR => {
             result = ProcResult::Value((MNC_CLOSE << 16) as isize);
         }

src/platform_impl/windows/window.rs

@@ -284,11 +284,16 @@ impl Window {
 
     #[inline]
     pub fn resize_increments(&self) -> Option<PhysicalSize<u32>> {
-        None
+        let w = self.window_state_lock();
+        let scale_factor = w.scale_factor;
+        w.resize_increments
+            .map(|size| size.to_physical(scale_factor))
     }
 
     #[inline]
-    pub fn set_resize_increments(&self, _increments: Option<Size>) {}
+    pub fn set_resize_increments(&self, increments: Option<Size>) {
+        self.window_state_lock().resize_increments = increments;
+    }
 
     #[inline]
     pub fn set_resizable(&self, resizable: bool) {

src/platform_impl/windows/window_state.rs

@@ -33,6 +33,8 @@ pub(crate) struct WindowState {
     pub min_size: Option<Size>,
     pub max_size: Option<Size>,
 
+    pub resize_increments: Option<Size>,
+
     pub window_icon: Option<Icon>,
     pub taskbar_icon: Option<Icon>,
 
@@ -155,6 +157,8 @@ impl WindowState {
             min_size: attributes.min_inner_size,
             max_size: attributes.max_inner_size,
 
+            resize_increments: attributes.resize_increments,
+
             window_icon: attributes.window_icon.clone(),
             taskbar_icon: None,
 

src/window.rs

@@ -893,7 +893,7 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// - **iOS / Android / Web / Wayland / Windows / Orbital:** Always returns [`None`].
+    /// - **iOS / Android / Web / Wayland / Orbital:** Always returns [`None`].
     #[inline]
     pub fn resize_increments(&self) -> Option<PhysicalSize<u32>> {
         let _span = tracing::debug_span!("winit::Window::resize_increments",).entered();
@@ -908,7 +908,7 @@ impl Window {
     /// ## Platform-specific
     ///
     /// - **macOS:** Increments are converted to logical size and then macOS rounds them to whole numbers.
-    /// - **Wayland / Windows:** Not implemented.
+    /// - **Wayland:** Not implemented.
     /// - **iOS / Android / Web / Orbital:** Unsupported.
     #[inline]
     pub fn set_resize_increments<S: Into<Size>>(&self, increments: Option<S>) {