Custom cursor images for all desktop platforms

CHANGELOG.md

@@ -11,6 +11,11 @@ Unreleased` header.
 
 # Unreleased
 
+- On Windows, macOS, X11, Wayland and Web, implement setting images as cursors. See the `custom_cursors.rs` example.
+  - Add `Window::set_custom_cursor`
+  - Add `CustomCursor`
+  - Add `CustomCursor::from_rgba` to allow creating cursor images from RGBA data.
+  - Add `CustomCursorExtWebSys::from_url` to allow loading cursor images from URLs.
 - On macOS, add services menu.
 - On macOS, remove spurious error logging when handling `Fn`.
 - On X11, fix an issue where floating point data from the server is

Cargo.toml

@@ -179,6 +179,7 @@ version = "0.3.64"
 features = [
     'AbortController',
     'AbortSignal',
+    'Blob',
     'console',
     'CssStyleDeclaration',
     'Document',
@@ -190,6 +191,10 @@ features = [
     'FocusEvent',
     'HtmlCanvasElement',
     'HtmlElement',
+    'ImageBitmap',
+    'ImageBitmapOptions',
+    'ImageBitmapRenderingContext',
+    'ImageData',
     'IntersectionObserver',
     'IntersectionObserverEntry',
     'KeyboardEvent',
@@ -199,14 +204,16 @@ features = [
     'Node',
     'PageTransitionEvent',
     'PointerEvent',
+    'PremultiplyAlpha',
     'ResizeObserver',
     'ResizeObserverBoxOptions',
     'ResizeObserverEntry',
     'ResizeObserverOptions',
     'ResizeObserverSize',
     'VisibilityState',
     'Window',
-    'WheelEvent'
+    'WheelEvent',
+    'Url',
 ]
 
 [target.'cfg(target_family = "wasm")'.dependencies]

FEATURES.md

@@ -106,6 +106,7 @@ If your PR makes notable changes to Winit's features, please update this section
 - **Cursor locking**: Locking the cursor inside the window so it cannot move.
 - **Cursor confining**: Confining the cursor to the window bounds so it cannot leave them.
 - **Cursor icon**: Changing the cursor icon or hiding the cursor.
+- **Cursor image**: Changing the cursor to your own image.
 - **Cursor hittest**: Handle or ignore mouse events for a window.
 - **Touch events**: Single-touch events.
 - **Touch pressure**: Touch events contain information about the amount of force being applied.
@@ -206,6 +207,7 @@ Legend:
 |Cursor locking          |❌       |✔️      |❌       |✔️          |**N/A**|**N/A**|✔️        |❌      |
 |Cursor confining        |✔️       |❌      |✔️       |✔️          |**N/A**|**N/A**|❌       |❌      |
 |Cursor icon             |✔️       |✔️      |✔️       |✔️          |**N/A**|**N/A**|✔️        |**N/A** |
+|Cursor image            |✔️       |✔️      |✔️       |✔️          |**N/A**|**N/A**|✔️        |**N/A** |
 |Cursor hittest          |✔️       |✔️      |✔️       |✔️          |**N/A**|**N/A**|❌        |❌      |
 |Touch events            |✔️       |❌      |✔️       |✔️          |✔️    |✔️     |✔️        |**N/A** |
 |Touch pressure          |✔️       |❌      |❌       |❌          |❌    |✔️     |✔️        |**N/A** |

examples/custom_cursors.rs

@@ -0,0 +1,92 @@
+#![allow(clippy::single_match, clippy::disallowed_methods)]
+
+#[cfg(not(wasm_platform))]
+use simple_logger::SimpleLogger;
+use winit::{
+    event::{ElementState, Event, KeyEvent, WindowEvent},
+    event_loop::EventLoop,
+    keyboard::Key,
+    window::{CustomCursor, WindowBuilder},
+};
+
+fn decode_cursor(bytes: &[u8]) -> CustomCursor {
+    let img = image::load_from_memory(bytes).unwrap().to_rgba8();
+    let samples = img.into_flat_samples();
+    let (_, w, h) = samples.extents();
+    let (w, h) = (w as u16, h as u16);
+    CustomCursor::from_rgba(samples.samples, w, h, w / 2, h / 2).unwrap()
+}
+
+#[cfg(not(wasm_platform))]
+#[path = "util/fill.rs"]
+mod fill;
+
+fn main() -> Result<(), impl std::error::Error> {
+    #[cfg(not(wasm_platform))]
+    SimpleLogger::new()
+        .with_level(log::LevelFilter::Info)
+        .init()
+        .unwrap();
+    #[cfg(wasm_platform)]
+    console_log::init_with_level(log::Level::Debug).unwrap();
+
+    let event_loop = EventLoop::new().unwrap();
+    let builder = WindowBuilder::new().with_title("A fantastic window!");
+    #[cfg(wasm_platform)]
+    let builder = {
+        use winit::platform::web::WindowBuilderExtWebSys;
+        builder.with_append(true)
+    };
+    let window = builder.build(&event_loop).unwrap();
+
+    let mut cursor_idx = 0;
+    let mut cursor_visible = true;
+
+    let custom_cursors = [
+        decode_cursor(include_bytes!("data/cross.png")),
+        decode_cursor(include_bytes!("data/cross2.png")),
+    ];
+
+    event_loop.run(move |event, _elwt| match event {
+        Event::WindowEvent { event, .. } => match event {
+            WindowEvent::KeyboardInput {
+                event:
+                    KeyEvent {
+                        state: ElementState::Pressed,
+                        logical_key: key,
+                        ..
+                    },
+                ..
+            } => match key.as_ref() {
+                Key::Character("1") => {
+                    log::debug!("Setting cursor to {:?}", cursor_idx);
+                    window.set_custom_cursor(&custom_cursors[cursor_idx]);
+                    cursor_idx = (cursor_idx + 1) % 2;
+                }
+                Key::Character("2") => {
+                    log::debug!("Setting cursor icon to default");
+                    window.set_cursor_icon(Default::default());
+                }
+                Key::Character("3") => {
+                    cursor_visible = !cursor_visible;
+                    log::debug!("Setting cursor visibility to {:?}", cursor_visible);
+                    window.set_cursor_visible(cursor_visible);
+                }
+                _ => {}
+            },
+            WindowEvent::RedrawRequested => {
+                #[cfg(not(wasm_platform))]
+                fill::fill_window(&window);
+            }
+            WindowEvent::CloseRequested => {
+                #[cfg(not(wasm_platform))]
+                _elwt.exit();
+            }
+            _ => (),
+        },
+        Event::AboutToWait => {
+            window.request_redraw();
+        }
+        _ => {}
+    })
+}

src/cursor.rs

@@ -0,0 +1,198 @@
+use core::fmt;
+use std::{error::Error, sync::Arc};
+
+use crate::platform_impl::PlatformCustomCursor;
+
+/// The maximum width and height for a cursor when using [`CustomCursor::from_rgba`].
+pub const MAX_CURSOR_SIZE: u16 = 2048;
+
+const PIXEL_SIZE: usize = 4;
+
+/// Use a custom image as a cursor (mouse pointer).
+///
+/// ## Platform-specific
+///
+/// **Web**: Some browsers have limits on cursor sizes usually at 128x128.
+///
+/// # Example
+///
+/// ```
+/// use winit::window::CustomCursor;
+///
+/// let w = 10;
+/// let h = 10;
+/// let rgba = vec![255; (w * h * 4) as usize];
+/// let custom_cursor = CustomCursor::from_rgba(rgba, w, h, w / 2, h / 2).unwrap();
+///
+/// #[cfg(target_family = "wasm")]
+/// let custom_cursor_url = {
+///     use winit::platform::web::CustomCursorExtWebSys;
+///     CustomCursor::from_url("http://localhost:3000/cursor.png", 0, 0).unwrap()
+/// };
+/// ```
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CustomCursor {
+    pub(crate) inner: Arc<PlatformCustomCursor>,
+}
+
+impl CustomCursor {
+    /// Creates a new cursor from an rgba buffer.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Web:** Setting cursor could be delayed due to the creation of `Blob` objects,
+    ///   which are async by nature.
+    pub fn from_rgba(
+        rgba: impl Into<Vec<u8>>,
+        width: u16,
+        height: u16,
+        hotspot_x: u16,
+        hotspot_y: u16,
+    ) -> Result<Self, BadImage> {
+        Ok(Self {
+            inner: PlatformCustomCursor::from_rgba(
+                rgba.into(),
+                width,
+                height,
+                hotspot_x,
+                hotspot_y,
+            )?
+            .into(),
+        })
+    }
+}
+
+/// An error produced when using [`CustomCursor::from_rgba`] with invalid arguments.
+#[derive(Debug, Clone)]
+pub enum BadImage {
+    /// Produced when the image dimensions are larger than [`MAX_CURSOR_SIZE`]. This doesn't
+    /// guarantee that the cursor will work, but should avoid many platform and device specific
+    /// limits.
+    TooLarge { width: u16, height: u16 },
+    /// Produced when the length of the `rgba` argument isn't divisible by 4, thus `rgba` can't be
+    /// safely interpreted as 32bpp RGBA pixels.
+    ByteCountNotDivisibleBy4 { byte_count: usize },
+    /// Produced when the number of pixels (`rgba.len() / 4`) isn't equal to `width * height`.
+    /// At least one of your arguments is incorrect.
+    DimensionsVsPixelCount {
+        width: u16,
+        height: u16,
+        width_x_height: u64,
+        pixel_count: u64,
+    },
+    /// Produced when the hotspot is outside the image bounds
+    HotspotOutOfBounds {
+        width: u16,
+        height: u16,
+        hotspot_x: u16,
+        hotspot_y: u16,
+    },
+}
+
+impl fmt::Display for BadImage {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            BadImage::TooLarge { width, height } => write!(f,
+                "The specified dimensions ({width:?}x{height:?}) are too large. The maximum is {MAX_CURSOR_SIZE:?}x{MAX_CURSOR_SIZE:?}.",
+            ),
+            BadImage::ByteCountNotDivisibleBy4 { byte_count } => write!(f,
+                "The length of the `rgba` argument ({byte_count:?}) isn't divisible by 4, making it impossible to interpret as 32bpp RGBA pixels.",
+            ),
+            BadImage::DimensionsVsPixelCount {
+                width,
+                height,
+                width_x_height,
+                pixel_count,
+            } => write!(f,
+                "The specified dimensions ({width:?}x{height:?}) don't match the number of pixels supplied by the `rgba` argument ({pixel_count:?}). For those dimensions, the expected pixel count is {width_x_height:?}.",
+            ),
+            BadImage::HotspotOutOfBounds {
+                width,
+                height,
+                hotspot_x,
+                hotspot_y,
+            } => write!(f,
+                "The specified hotspot ({hotspot_x:?}, {hotspot_y:?}) is outside the image bounds ({width:?}x{height:?}).",
+            ),
+        }
+    }
+}
+
+impl Error for BadImage {}
+
+/// Platforms export this directly as `PlatformCustomCursor` if they need to only work with images.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CursorImage {
+    pub(crate) rgba: Vec<u8>,
+    pub(crate) width: u16,
+    pub(crate) height: u16,
+    pub(crate) hotspot_x: u16,
+    pub(crate) hotspot_y: u16,
+}
+
+#[allow(dead_code)]
+impl CursorImage {
+    pub fn from_rgba(
+        rgba: Vec<u8>,
+        width: u16,
+        height: u16,
+        hotspot_x: u16,
+        hotspot_y: u16,
+    ) -> Result<Self, BadImage> {
+        if width > MAX_CURSOR_SIZE || height > MAX_CURSOR_SIZE {
+            return Err(BadImage::TooLarge { width, height });
+        }
+
+        if rgba.len() % PIXEL_SIZE != 0 {
+            return Err(BadImage::ByteCountNotDivisibleBy4 {
+                byte_count: rgba.len(),
+            });
+        }
+
+        let pixel_count = (rgba.len() / PIXEL_SIZE) as u64;
+        let width_x_height = width as u64 * height as u64;
+        if pixel_count != width_x_height {
+            return Err(BadImage::DimensionsVsPixelCount {
+                width,
+                height,
+                width_x_height,
+                pixel_count,
+            });
+        }
+
+        if hotspot_x >= width || hotspot_y >= height {
+            return Err(BadImage::HotspotOutOfBounds {
+                width,
+                height,
+                hotspot_x,
+                hotspot_y,
+            });
+        }
+
+        Ok(CursorImage {
+            rgba,
+            width,
+            height,
+            hotspot_x,
+            hotspot_y,
+        })
+    }
+}
+
+// Platforms that don't support cursors will export this as `PlatformCustomCursor`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) struct NoCustomCursor;
+
+#[allow(dead_code)]
+impl NoCustomCursor {
+    pub fn from_rgba(
+        rgba: Vec<u8>,
+        width: u16,
+        height: u16,
+        hotspot_x: u16,
+        hotspot_y: u16,
+    ) -> Result<Self, BadImage> {
+        CursorImage::from_rgba(rgba, width, height, hotspot_x, hotspot_y)?;
+        Ok(Self)
+    }
+}

src/lib.rs

@@ -172,6 +172,7 @@ extern crate bitflags;
 pub mod dpi;
 #[macro_use]
 pub mod error;
+mod cursor;
 pub mod event;
 pub mod event_loop;
 mod icon;