Handle set_mouse_cursor method on windows (#186)

This adds the ability to change the cursor on Windows platforms. For some reason there are very few default cursors included in Windows so a lot of cursors available on other platforms aren't available yet, which is why many of the `MouseCursor` options just maps to `IDC_ARROW`. I'll look into adding custom cursors next.

`LoadCursorW` is supposedly superseded by [LoadImageW](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadcursorw) but I couldn't find a way to do it with that one that doesn't crash. 

Tested with Vizia's cursor icon example [here](https://github.com/Fredemus/vizia/tree/baseview-window-events) and everything seems to work as it should.
Also tested by hovering over some buttons on a plugin.

src/win/cursor.rs

@@ -0,0 +1,54 @@
+use crate::MouseCursor;
+use winapi::{
+    shared::ntdef::LPCWSTR,
+    um::winuser::{
+        IDC_APPSTARTING, IDC_ARROW, IDC_CROSS, IDC_HAND, IDC_HELP, IDC_IBEAM, IDC_NO, IDC_SIZEALL,
+        IDC_SIZENESW, IDC_SIZENS, IDC_SIZENWSE, IDC_SIZEWE, IDC_WAIT,
+    },
+};
+
+pub fn cursor_to_lpcwstr(cursor: MouseCursor) -> LPCWSTR {
+    match cursor {
+        MouseCursor::Default => IDC_ARROW,
+        MouseCursor::Hand => IDC_HAND,
+        MouseCursor::HandGrabbing => IDC_SIZEALL,
+        MouseCursor::Help => IDC_HELP,
+        // an empty LPCWSTR results in the cursor being hidden
+        MouseCursor::Hidden => std::ptr::null(),
+
+        MouseCursor::Text => IDC_IBEAM,
+        MouseCursor::VerticalText => IDC_IBEAM,
+
+        MouseCursor::Working => IDC_WAIT,
+        MouseCursor::PtrWorking => IDC_APPSTARTING,
+
+        MouseCursor::NotAllowed => IDC_NO,
+        MouseCursor::PtrNotAllowed => IDC_NO,
+
+        MouseCursor::ZoomIn => IDC_ARROW,
+        MouseCursor::ZoomOut => IDC_ARROW,
+
+        MouseCursor::Alias => IDC_ARROW,
+        MouseCursor::Copy => IDC_ARROW,
+        MouseCursor::Move => IDC_SIZEALL,
+        MouseCursor::AllScroll => IDC_SIZEALL,
+        MouseCursor::Cell => IDC_CROSS,
+        MouseCursor::Crosshair => IDC_CROSS,
+
+        MouseCursor::EResize => IDC_SIZEWE,
+        MouseCursor::NResize => IDC_SIZENS,
+        MouseCursor::NeResize => IDC_SIZENESW,
+        MouseCursor::NwResize => IDC_SIZENWSE,
+        MouseCursor::SResize => IDC_SIZENS,
+        MouseCursor::SeResize => IDC_SIZENWSE,
+        MouseCursor::SwResize => IDC_SIZENESW,
+        MouseCursor::WResize => IDC_SIZEWE,
+        MouseCursor::EwResize => IDC_SIZEWE,
+        MouseCursor::NsResize => IDC_SIZENS,
+        MouseCursor::NwseResize => IDC_SIZENWSE,
+        MouseCursor::NeswResize => IDC_SIZENESW,
+
+        MouseCursor::ColResize => IDC_SIZEWE,
+        MouseCursor::RowResize => IDC_SIZENS,
+    }
+}

src/win/mod.rs

@@ -1,3 +1,4 @@
+mod cursor;
 mod drop_target;
 mod keyboard;
 mod window;

src/win/window.rs

@@ -1,5 +1,5 @@
 use winapi::shared::guiddef::GUID;
-use winapi::shared::minwindef::{ATOM, FALSE, LPARAM, LRESULT, UINT, WPARAM};
+use winapi::shared::minwindef::{ATOM, FALSE, LOWORD, LPARAM, LRESULT, UINT, WPARAM};
 use winapi::shared::windef::{HWND, RECT};
 use winapi::um::combaseapi::CoCreateGuid;
 use winapi::um::ole2::{OleInitialize, RegisterDragDrop, RevokeDragDrop};
@@ -7,15 +7,16 @@ use winapi::um::oleidl::LPDROPTARGET;
 use winapi::um::winuser::{
     AdjustWindowRectEx, CreateWindowExW, DefWindowProcW, DestroyWindow, DispatchMessageW,
     GetDpiForWindow, GetFocus, GetMessageW, GetWindowLongPtrW, LoadCursorW, PostMessageW,
-    RegisterClassW, ReleaseCapture, SetCapture, SetFocus, SetProcessDpiAwarenessContext, SetTimer,
-    SetWindowLongPtrW, SetWindowPos, TrackMouseEvent, TranslateMessage, UnregisterClassW, CS_OWNDC,
-    GET_XBUTTON_WPARAM, GWLP_USERDATA, IDC_ARROW, MSG, SWP_NOMOVE, SWP_NOZORDER, TRACKMOUSEEVENT,
-    WHEEL_DELTA, WM_CHAR, WM_CLOSE, WM_CREATE, WM_DPICHANGED, WM_INPUTLANGCHANGE, WM_KEYDOWN,
-    WM_KEYUP, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MOUSEHWHEEL,
-    WM_MOUSELEAVE, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCDESTROY, WM_RBUTTONDOWN, WM_RBUTTONUP,
-    WM_SHOWWINDOW, WM_SIZE, WM_SYSCHAR, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TIMER, WM_USER,
-    WM_XBUTTONDOWN, WM_XBUTTONUP, WNDCLASSW, WS_CAPTION, WS_CHILD, WS_CLIPSIBLINGS, WS_MAXIMIZEBOX,
-    WS_MINIMIZEBOX, WS_POPUPWINDOW, WS_SIZEBOX, WS_VISIBLE, XBUTTON1, XBUTTON2,
+    RegisterClassW, ReleaseCapture, SetCapture, SetCursor, SetFocus, SetProcessDpiAwarenessContext,
+    SetTimer, SetWindowLongPtrW, SetWindowPos, TrackMouseEvent, TranslateMessage, UnregisterClassW,
+    CS_OWNDC, GET_XBUTTON_WPARAM, GWLP_USERDATA, HTCLIENT, IDC_ARROW, MSG, SWP_NOMOVE,
+    SWP_NOZORDER, TRACKMOUSEEVENT, WHEEL_DELTA, WM_CHAR, WM_CLOSE, WM_CREATE, WM_DPICHANGED,
+    WM_INPUTLANGCHANGE, WM_KEYDOWN, WM_KEYUP, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN,
+    WM_MBUTTONUP, WM_MOUSEHWHEEL, WM_MOUSELEAVE, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCDESTROY,
+    WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR, WM_SHOWWINDOW, WM_SIZE, WM_SYSCHAR, WM_SYSKEYDOWN,
+    WM_SYSKEYUP, WM_TIMER, WM_USER, WM_XBUTTONDOWN, WM_XBUTTONUP, WNDCLASSW, WS_CAPTION, WS_CHILD,
+    WS_CLIPSIBLINGS, WS_MAXIMIZEBOX, WS_MINIMIZEBOX, WS_POPUPWINDOW, WS_SIZEBOX, WS_VISIBLE,
+    XBUTTON1, XBUTTON2,
 };
 
 use std::cell::{Cell, Ref, RefCell, RefMut};
@@ -37,6 +38,7 @@ use crate::{
     WindowHandler, WindowInfo, WindowOpenOptions, WindowScalePolicy,
 };
 
+use super::cursor::cursor_to_lpcwstr;
 use super::drop_target::DropTarget;
 use super::keyboard::KeyboardState;
 
@@ -428,6 +430,24 @@ unsafe fn wnd_proc_inner(
 
             None
         }
+        // If WM_SETCURSOR returns `None`, WM_SETCURSOR continues to get handled by the outer window(s),
+        // If it returns `Some(1)`, the current window decides what the cursor is
+        WM_SETCURSOR => {
+            let low_word = LOWORD(lparam as u32) as isize;
+            let mouse_in_window = low_word == HTCLIENT;
+            if mouse_in_window {
+                // Here we need to set the cursor back to what the state says, since it can have changed when outside the window
+                let cursor =
+                    LoadCursorW(null_mut(), cursor_to_lpcwstr(window_state.cursor_icon.get()));
+                unsafe {
+                    SetCursor(cursor);
+                }
+                Some(1)
+            } else {
+                // Cursor is being changed by some other window, e.g. when having mouse on the borders to resize it
+                None
+            }
+        }
         // NOTE: `WM_NCDESTROY` is handled in the outer function because this deallocates the window
         //        state
         BV_WINDOW_MUST_CLOSE => {
@@ -480,6 +500,7 @@ pub(super) struct WindowState {
     keyboard_state: RefCell<KeyboardState>,
     mouse_button_counter: Cell<usize>,
     mouse_was_outside_window: RefCell<bool>,
+    cursor_icon: Cell<MouseCursor>,
     // Initialized late so the `Window` can hold a reference to this `WindowState`
     handler: RefCell<Option<Box<dyn WindowHandler>>>,
     _drop_target: RefCell<Option<Rc<DropTarget>>>,
@@ -685,6 +706,7 @@ impl Window<'_> {
                 keyboard_state: RefCell::new(KeyboardState::new()),
                 mouse_button_counter: Cell::new(0),
                 mouse_was_outside_window: RefCell::new(true),
+                cursor_icon: Cell::new(MouseCursor::Default),
                 // The Window refers to this `WindowState`, so this `handler` needs to be
                 // initialized later
                 handler: RefCell::new(None),
@@ -790,8 +812,12 @@ impl Window<'_> {
         self.state.deferred_tasks.borrow_mut().push_back(task);
     }
 
-    pub fn set_mouse_cursor(&mut self, _mouse_cursor: MouseCursor) {
-        todo!()
+    pub fn set_mouse_cursor(&mut self, mouse_cursor: MouseCursor) {
+        self.state.cursor_icon.set(mouse_cursor);
+        unsafe {
+            let cursor = LoadCursorW(null_mut(), cursor_to_lpcwstr(mouse_cursor));
+            SetCursor(cursor);
+        }
     }
 
     #[cfg(feature = "opengl")]