waybackend-cursor 0.10.1

//! Wayland cursor implementation using `Waybackend` as the backend
//!
//! This crate was make by adapting the code in `wayland-cursor-rs`, from the `smithay` project.
//!
//! Key differences:
//!
//!  - we do not allow automatically setting cursor fallbacks. You'd have to do something manually
//!    every time
//!  - when loading a cursor, you must pass closures for running the wayland specific code. There
//!    are examples of how to do this in the documentation
use waybackend::{Waybackend, types::ObjectId};

#[derive(Debug)]
pub enum CursorLoadError {
    Io(rustix::io::Errno),
    EnvVar(std::env::VarError),
}

impl core::error::Error for CursorLoadError {
    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
        match self {
            CursorLoadError::Io(errno) => errno.source(),
            CursorLoadError::EnvVar(var_error) => var_error.source(),
        }
    }

    fn cause(&self) -> Option<&dyn core::error::Error> {
        self.source()
    }
}

impl core::fmt::Display for CursorLoadError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "CursorLoadError: ")?;
        match self {
            CursorLoadError::Io(errno) => errno.fmt(f),
            CursorLoadError::EnvVar(var_error) => var_error.fmt(f),
        }
    }
}

pub struct CursorTheme {
    name: String,
    cursors: Vec<Cursor>,
    /// cursor size
    size: u32,
    wl_shm_pool: ObjectId,
    pool_size: u32,
    pool_len: u32,
    shm_fd: rustix::fd::OwnedFd,
}

impl CursorTheme {
    /// Use this to create the initial pool
    const INITIAL_POOL_SIZE: usize = 16 * 16 * 4;

    /// Tries to load the cursor theme from the `XCURSOR_THEME` and `XCURSOR_SIZE` environment variables
    ///
    /// See [`CursorTheme::load_from_name`] for an example of a `create_pool_fn`.
    #[inline]
    pub fn load_from_env<F>(mut size: u32, create_pool_fn: F) -> Result<Self, CursorLoadError>
    where
        F: FnOnce(&rustix::fd::OwnedFd, u32) -> ObjectId,
    {
        let name = &std::env::var("XCURSOR_THEME").map_err(CursorLoadError::EnvVar)?;

        if let Ok(var) = std::env::var("XCURSOR_SIZE")
            && let Ok(int) = var.parse()
        {
            size = int;
        }

        Self::load_from_name(name, size, create_pool_fn)
    }

    /// Tries to load the cursor theme from an `str`
    ///
    /// `create_pool_fn` is a function that takes the shm file descriptor and the initial size.
    /// Typically, it will look like this (note in the example we are loading the generatec wayland
    /// glue code with `waybackend-scanner` in a module called `wayland`):
    ///
    /// ```ignore
    /// use waybackend_cursor::CursorTheme;
    /// use waybackend::{types::ObjectId, objman, Waybackend};
    ///
    /// #[derive(Clone, Copy, Debug, PartialEq)]
    /// enum WaylandObject {
    ///     Display,
    ///     Shm,
    ///     ShmPool,
    ///     Buffer,
    ///     Surface,
    ///     // ...
    /// }
    ///
    /// fn load_cursor(
    ///     backend: &mut Waybackend,
    ///     objman: &mut objman::ObjectManager::<WaylandObject>,
    ///     wayland_shm: ObjectId) -> CursorTheme {
    ///     CursorTheme::load_from_name("default", 24, |fd, size| {
    ///         let shm_pool = objman.create(WaylandObject::ShmPool);
    ///         wayland::wl_shm::req::create_pool(
    ///             backend,
    ///             wayland_shm,
    ///             shm_pool,
    ///             fd,
    ///             size as i32,
    ///         )
    ///         .unwrap();
    ///         shm_pool
    ///     }).unwrap()
    /// }
    /// ```
    #[inline]
    pub fn load_from_name<F>(
        name: &str,
        size: u32,
        create_pool_fn: F,
    ) -> Result<Self, CursorLoadError>
    where
        F: FnOnce(&rustix::fd::OwnedFd, u32) -> ObjectId,
    {
        //  Create shm.
        let shm_fd = waybackend::shm::create().map_err(CursorLoadError::Io)?;
        rustix::fs::ftruncate(&shm_fd, Self::INITIAL_POOL_SIZE as u64)
            .map_err(CursorLoadError::Io)?;
        let wl_shm_pool = create_pool_fn(&shm_fd, size);

        let name = String::from(name);
        Ok(Self {
            name,
            size,
            pool_size: Self::INITIAL_POOL_SIZE as u32,
            pool_len: 0,
            cursors: Vec::new(),
            wl_shm_pool,
            shm_fd,
        })
    }

    /// Gets a cursor from the theme
    ///
    ///  - `backend` will be fed to the two functions.
    ///  - `create_buffer_fn` is a closure that returns  a `ObjectId`: the ObjectId of the
    ///    newly created wayland buffer. It accepts 6 inputs:
    ///    * backend (should be `waybackend::Waybackend`)
    ///    * the `wl_shm_pool` ObjectId
    ///    * offset (see the wayland protocol documentation)
    ///    * width  (see the wayland protocol documentation)
    ///    * height (see the wayland protocol documentation)
    ///    * stride (see the wayland protocol documentation)
    ///  - `resize_fn` is a closure that resizes the `wl_shm_pool`. It accepts 3 inputs:
    ///    * the backend (should be `waybackend::Waybackend`)
    ///    * the `wl_shm_pool` ObjectId
    ///    * the new size
    ///
    /// Here is an example of what this function call could look like:
    ///
    /// ```ignore
    /// use waybackend::{types::ObjectId, objman::Objman, Waybackend};
    /// use waybackend_cursor::{Cursor, CursorTheme};
    /// fn get_cursor(
    ///     cursor_theme: &mut CursorTheme,
    ///     backend: &mut Waybackend,
    ///     objman: &mut Objman,
    ///     name: &str,
    /// ) -> Option<&Cursor> {
    ///     cursor_theme.get_cursor(
    ///         name,
    ///         backend,
    ///         |backend, pool, offset, width, height, stride| {
    ///             // NOTE: you probably also want to store this buffer id somewhere
    ///             let buffer = objman.create(WaylandObject::Buffer);
    ///             wayland::wl_shm_pool::req::create_buffer(
    ///                 backend,
    ///                 pool,
    ///                 buffer,
    ///                 offset,
    ///                 width,
    ///                 height,
    ///                 stride,
    ///                 wayland::wl_shm::Format::argb8888,
    ///             )
    ///             .unwrap();
    ///             buffer
    ///         },
    ///         |backend, id, size| {
    ///             wayland::wl_shm_pool::req::resize(backend, id, size as i32).unwrap()
    ///         },
    ///     )
    /// }
    /// ```
    #[inline]
    pub fn get_cursor<F1, F2>(
        &mut self,
        name: &str,
        backend: &mut Waybackend,
        create_buffer_fn: F1,
        resize_fn: F2,
    ) -> Option<&Cursor>
    where
        F1: FnMut(&mut Waybackend, ObjectId, i32, i32, i32, i32) -> ObjectId,
        F2: FnMut(&mut Waybackend, ObjectId, u32),
    {
        match self.cursors.iter().position(|cursor| cursor.name == name) {
            Some(i) => Some(&self.cursors[i]),
            None => {
                let cursor =
                    self.load_cursor(name, self.size, backend, create_buffer_fn, resize_fn)?;
                self.cursors.push(cursor);
                self.cursors.last()
            }
        }
    }

    #[inline]
    fn load_cursor<F1, F2>(
        &mut self,
        name: &str,
        size: u32,
        backend: &mut Waybackend,
        create_buffer_fn: F1,
        resize_fn: F2,
    ) -> Option<Cursor>
    where
        F1: FnMut(&mut Waybackend, ObjectId, i32, i32, i32, i32) -> ObjectId,
        F2: FnMut(&mut Waybackend, ObjectId, u32),
    {
        use rustix::{buffer, fs, io};
        let icon_path = xcursor::CursorTheme::load(&self.name).load_icon(name)?;
        let icon_file = fs::open(icon_path, fs::OFlags::RDONLY, fs::Mode::RUSR).ok()?;

        let mut buf = Vec::with_capacity(4096);
        loop {
            match io::retry_on_intr(|| io::read(&icon_file, buffer::spare_capacity(&mut buf))) {
                Ok(0) => break,
                Err(_) => return None,
                Ok(_) => (),
            }

            if buf.capacity() == buf.len() {
                buf.reserve(buf.capacity() * 2);
            }
        }
        let images = xcursor::parser::parse_xcursor(&buf)?;

        Some(Cursor::new(
            name,
            self,
            &images,
            size,
            backend,
            create_buffer_fn,
            resize_fn,
        ))
    }

    #[inline]
    fn grow<F>(&mut self, backend: &mut Waybackend, size: u32, resize_fn: F)
    where
        F: FnOnce(&mut Waybackend, ObjectId, u32),
    {
        if size > self.pool_size {
            rustix::fs::ftruncate(&self.shm_fd, size as u64)
                .expect("failed to new cursor buffer length");
            resize_fn(backend, self.wl_shm_pool, size);
            self.pool_size = size;
        }
    }
}

pub struct Cursor {
    name: String,
    images: Vec<CursorImageBuffer>,
    total_duration: u32,
}

impl Cursor {
    #[inline]
    fn new<F1, F2>(
        name: &str,
        theme: &mut CursorTheme,
        images: &[xcursor::parser::Image],
        size: u32,
        backend: &mut Waybackend,
        mut create_buffer_fn: F1,
        mut resize_fn: F2,
    ) -> Self
    where
        F1: FnMut(&mut Waybackend, ObjectId, i32, i32, i32, i32) -> ObjectId,
        F2: FnMut(&mut Waybackend, ObjectId, u32),
    {
        let mut total_duration = 0;
        let f1 = &mut create_buffer_fn;
        let f2 = &mut resize_fn;
        let images: Vec<CursorImageBuffer> = Self::nearest_images(size, images)
            .map(|image| {
                let buffer =
                    CursorImageBuffer::new::<&mut F1, &mut F2>(theme, image, backend, f1, f2);
                total_duration += buffer.delay;

                buffer
            })
            .collect();

        Self {
            total_duration,
            name: String::from(name),
            images,
        }
    }

    #[inline]
    fn nearest_images(
        size: u32,
        images: &[xcursor::parser::Image],
    ) -> impl Iterator<Item = &xcursor::parser::Image> {
        // Follow the nominal size of the cursor to choose the nearest
        let nearest_image = images
            .iter()
            .min_by_key(|image| (size as i32 - image.size as i32).abs())
            .unwrap();
        images.iter().filter(move |image| {
            image.width == nearest_image.width && image.height == nearest_image.height
        })
    }

    /// Time is returned in milliseconds
    #[inline]
    pub fn frame_and_duration(&self, mut millis: u32) -> (usize, u32) {
        millis %= self.total_duration;
        let mut res = 0;
        for (i, img) in self.images.iter().enumerate() {
            if millis < img.delay {
                res = i;
                break;
            }
            millis -= img.delay;
        }

        (res, millis)
    }

    #[inline]
    pub fn images(&self) -> &[CursorImageBuffer] {
        &self.images
    }
}

pub struct CursorImageBuffer {
    wl_buffer: ObjectId,
    delay: u32,
    xhot: u32,
    yhot: u32,
    width: u32,
    height: u32,
}

impl CursorImageBuffer {
    /// Construct a new CursorImageBuffer
    ///
    /// This function appends the pixels of the image to the provided file,
    /// and constructs a wl_buffer on that data.
    #[inline]
    fn new<F1, F2>(
        theme: &mut CursorTheme,
        image: &xcursor::parser::Image,
        backend: &mut Waybackend,
        create_buffer_fn: F1,
        resize_fn: F2,
    ) -> Self
    where
        F1: FnOnce(&mut Waybackend, ObjectId, i32, i32, i32, i32) -> ObjectId,
        F2: FnOnce(&mut Waybackend, ObjectId, u32),
    {
        use rustix::mm::{MapFlags, ProtFlags, mmap, munmap};
        let buf = &image.pixels_rgba;
        let offset = theme.pool_len as u64;
        // Resize memory before writing to it to handle shm correctly.
        let new_size = offset + buf.len() as u64;
        theme.grow(backend, new_size as u32, resize_fn);
        let mmap = unsafe {
            mmap(
                core::ptr::null_mut(),
                new_size as usize,
                ProtFlags::READ | ProtFlags::WRITE,
                MapFlags::SHARED,
                &theme.shm_fd,
                0,
            )
        }
        .expect("failed to mmap cursor shared memory");
        {
            let slice = unsafe {
                core::slice::from_raw_parts_mut(mmap.cast::<u8>().add(offset as usize), buf.len())
            };
            slice.copy_from_slice(buf);
        }
        theme.pool_len += buf.len() as u32;

        let wl_buffer = create_buffer_fn(
            backend,
            theme.wl_shm_pool,
            offset as i32,
            image.width as i32,
            image.height as i32,
            (image.width * 4) as i32,
        );

        unsafe { munmap(mmap, new_size as usize).expect("failed to munmap cursor shared memory") };
        Self {
            wl_buffer,
            delay: image.delay,
            xhot: image.xhot,
            yhot: image.yhot,
            width: image.width,
            height: image.height,
        }
    }

    /// Dimensions of this image
    #[inline]
    pub fn dimensions(&self) -> (u32, u32) {
        (self.width, self.height)
    }

    /// Location of the pointer hotspot in this image
    #[inline]
    pub fn hotspot(&self) -> (u32, u32) {
        (self.xhot, self.yhot)
    }

    /// Time (in milliseconds) for which this image should be displayed
    #[inline]
    pub fn delay(&self) -> u32 {
        self.delay
    }

    /// The wayland buffer
    #[inline]
    pub fn wl_buffer(&self) -> ObjectId {
        self.wl_buffer
    }
}