feat(all): Custom cursor images for all desktop platforms

There seems to be many PRs relating to this issue, but they don't include all
platforms and for some reason lost steam. This PR again tries to make this
feature happen, and does it for all desktop platforms (x11, wayland, macos,
windows, web).

I think the best user of this feature and the reason I'm doing this is Bevy and
game engines in general. There non laggy hardware cursors with custom images are
very important. Game devs also like their PNGs so supporting platform native
cursor files is not that important, but I guess could be added too.

Co-authored-by: daxpedda <daxpedda@gmail.com>
Co-authored-by: Mads Marquart <mads@marquart.dk>
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

src/platform_impl/linux/x11/util/cursor.rs

@@ -1,9 +1,8 @@
-use std::ffi::CString;
-use std::iter;
+use std::{ffi::CString, iter, slice, sync::Arc};
 
 use x11rb::connection::Connection;
 
-use crate::window::CursorIcon;
+use crate::{cursor::CursorImage, window::CursorIcon};
 
 use super::*;
 
@@ -20,6 +19,11 @@ impl XConnection {
             .expect("Failed to set cursor");
     }
 
+    pub fn set_custom_cursor(&self, window: xproto::Window, cursor: &CustomCursor) {
+        self.update_cursor(window, cursor.inner.cursor)
+            .expect("Failed to set cursor");
+    }
+
     fn create_empty_cursor(&self) -> ffi::Cursor {
         let data = 0;
         let pixmap = unsafe {
@@ -87,3 +91,74 @@ impl XConnection {
         Ok(())
     }
 }
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SelectedCursor {
+    Custom(CustomCursor),
+    Named(CursorIcon),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CustomCursor {
+    inner: Arc<CustomCursorInner>,
+}
+
+impl CustomCursor {
+    pub(crate) unsafe fn new(xconn: &Arc<XConnection>, image: &CursorImage) -> Self {
+        unsafe {
+            let ximage =
+                (xconn.xcursor.XcursorImageCreate)(image.width as i32, image.height as i32);
+            if ximage.is_null() {
+                panic!("failed to allocate cursor image");
+            }
+            (*ximage).xhot = image.hotspot_x as u32;
+            (*ximage).yhot = image.hotspot_y as u32;
+            (*ximage).delay = 0;
+
+            let dst = slice::from_raw_parts_mut((*ximage).pixels, image.rgba.len() / 4);
+            for (dst, chunk) in dst.iter_mut().zip(image.rgba.chunks_exact(4)) {
+                *dst = (chunk[0] as u32) << 16
+                    | (chunk[1] as u32) << 8
+                    | (chunk[2] as u32)
+                    | (chunk[3] as u32) << 24;
+            }
+
+            let cursor = (xconn.xcursor.XcursorImageLoadCursor)(xconn.display, ximage);
+            (xconn.xcursor.XcursorImageDestroy)(ximage);
+            Self {
+                inner: Arc::new(CustomCursorInner {
+                    xconn: xconn.clone(),
+                    cursor,
+                }),
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+struct CustomCursorInner {
+    xconn: Arc<XConnection>,
+    cursor: ffi::Cursor,
+}
+
+impl Drop for CustomCursorInner {
+    fn drop(&mut self) {
+        unsafe {
+            (self.xconn.xlib.XFreeCursor)(self.xconn.display, self.cursor);
+        }
+    }
+}
+
+impl PartialEq for CustomCursorInner {
+    fn eq(&self, other: &Self) -> bool {
+        self.cursor == other.cursor
+    }
+}
+
+impl Eq for CustomCursorInner {}
+
+impl Default for SelectedCursor {
+    fn default() -> Self {
+        SelectedCursor::Named(Default::default())
+    }
+}

src/platform_impl/linux/x11/util/mod.rs

@@ -13,7 +13,7 @@ mod randr;
 mod window_property;
 mod wm;
 
-pub use self::{geometry::*, hint::*, input::*, window_property::*, wm::*};
+pub use self::{cursor::*, geometry::*, hint::*, input::*, window_property::*, wm::*};
 
 use std::{
     mem::{self, MaybeUninit},

src/platform_impl/linux/x11/window.rs

@@ -7,6 +7,9 @@ use std::{
     sync::{Arc, Mutex, MutexGuard},
 };
 
+use crate::cursor::CustomCursor as RootCustomCursor;
+
+use cursor_icon::CursorIcon;
 use x11rb::{
     connection::Connection,
     properties::{WmHints, WmHintsState, WmSizeHints, WmSizeHintsSpecification},
@@ -33,13 +36,15 @@ use crate::{
         PlatformSpecificWindowBuilderAttributes, VideoMode as PlatformVideoMode,
     },
     window::{
-        CursorGrabMode, CursorIcon, ImePurpose, ResizeDirection, Theme, UserAttentionType,
-        WindowAttributes, WindowButtons, WindowLevel,
+        CursorGrabMode, ImePurpose, ResizeDirection, Theme, UserAttentionType, WindowAttributes,
+        WindowButtons, WindowLevel,
     },
 };
 
 use super::{
-    ffi, util, CookieResultExt, EventLoopWindowTarget, ImeRequest, ImeSender, VoidCookie, WindowId,
+    ffi,
+    util::{self, CustomCursor, SelectedCursor},
+    CookieResultExt, EventLoopWindowTarget, ImeRequest, ImeSender, VoidCookie, WindowId,
     XConnection,
 };
 
@@ -126,7 +131,7 @@ pub(crate) struct UnownedWindow {
     root: xproto::Window,               // never changes
     #[allow(dead_code)]
     screen_id: i32, // never changes
-    cursor: Mutex<CursorIcon>,
+    selected_cursor: Mutex<SelectedCursor>,
     cursor_grabbed_mode: Mutex<CursorGrabMode>,
     #[allow(clippy::mutex_atomic)]
     cursor_visible: Mutex<bool>,
@@ -355,7 +360,7 @@ impl UnownedWindow {
             visual,
             root,
             screen_id,
-            cursor: Default::default(),
+            selected_cursor: Default::default(),
             cursor_grabbed_mode: Mutex::new(CursorGrabMode::None),
             cursor_visible: Mutex::new(true),
             ime_sender: Mutex::new(event_loop.ime_sender.clone()),
@@ -1535,13 +1540,29 @@ impl UnownedWindow {
 
     #[inline]
     pub fn set_cursor_icon(&self, cursor: CursorIcon) {
-        let old_cursor = replace(&mut *self.cursor.lock().unwrap(), cursor);
+        let old_cursor = replace(
+            &mut *self.selected_cursor.lock().unwrap(),
+            SelectedCursor::Named(cursor),
+        );
+
         #[allow(clippy::mutex_atomic)]
-        if cursor != old_cursor && *self.cursor_visible.lock().unwrap() {
+        if SelectedCursor::Named(cursor) != old_cursor && *self.cursor_visible.lock().unwrap() {
             self.xconn.set_cursor_icon(self.xwindow, Some(cursor));
         }
     }
 
+    #[inline]
+    pub fn set_custom_cursor(&self, cursor: RootCustomCursor) {
+        let new_cursor = unsafe { CustomCursor::new(&self.xconn, &cursor.inner) };
+
+        #[allow(clippy::mutex_atomic)]
+        if *self.cursor_visible.lock().unwrap() {
+            self.xconn.set_custom_cursor(self.xwindow, &new_cursor);
+        }
+
+        *self.selected_cursor.lock().unwrap() = SelectedCursor::Custom(new_cursor);
+    }
+
     #[inline]
     pub fn set_cursor_grab(&self, mode: CursorGrabMode) -> Result<(), ExternalError> {
         let mut grabbed_lock = self.cursor_grabbed_mode.lock().unwrap();
@@ -1628,13 +1649,23 @@ impl UnownedWindow {
             return;
         }
         let cursor = if visible {
-            Some(*self.cursor.lock().unwrap())
+            Some((*self.selected_cursor.lock().unwrap()).clone())
         } else {
             None
         };
         *visible_lock = visible;
         drop(visible_lock);
-        self.xconn.set_cursor_icon(self.xwindow, cursor);
+        match cursor {
+            Some(SelectedCursor::Custom(cursor)) => {
+                self.xconn.set_custom_cursor(self.xwindow, &cursor);
+            }
+            Some(SelectedCursor::Named(cursor)) => {
+                self.xconn.set_cursor_icon(self.xwindow, Some(cursor));
+            }
+            None => {
+                self.xconn.set_cursor_icon(self.xwindow, None);
+            }
+        }
     }
 
     #[inline]