smithay_client_toolkit/shm/
multi.rs

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1//! A pool implementation which automatically manage buffers.
2//!
3//! This pool is built on the [`RawPool`].
4//!
5//! The [`MultiPool`] takes a key which is used to identify buffers and tries to return the buffer associated to the key
6//! if possible. If no buffer in the pool is associated to the key, it will create a new one.
7//!
8//! # Example
9//!
10//! ```rust
11//! use smithay_client_toolkit::reexports::client::{
12//!     QueueHandle,
13//!     protocol::wl_surface::WlSurface,
14//!     protocol::wl_shm::Format,
15//! };
16//! use smithay_client_toolkit::shm::multi::MultiPool;
17//!
18//! struct WlFoo {
19//!     // The surface we'll draw on and the index of buffer associated to it
20//!     surface: (WlSurface, usize),
21//!     pool: MultiPool<(WlSurface, usize)>
22//! }
23//!
24//! impl WlFoo {
25//!     fn draw(&mut self, qh: &QueueHandle<WlFoo>) {
26//!         let surface = &self.surface.0;
27//!         // We'll increment "i" until the pool can create a new buffer
28//!         // if there's no buffer associated with our surface and "i" or if
29//!         // a buffer with the obuffer associated with our surface and "i" is free for use.
30//!         //
31//!         // There's no limit to the amount of buffers we can allocate to our surface but since
32//!         // shm buffers are released fairly fast, it's unlikely we'll need more than double buffering.
33//!         for i in 0..2 {
34//!             self.surface.1 = i;
35//!             if let Ok((offset, buffer, slice)) = self.pool.create_buffer(
36//!                 100,
37//!                 100 * 4,
38//!                 100,
39//!                 &self.surface,
40//!                 Format::Argb8888,
41//!             ) {
42//!                 /*
43//!                     insert drawing code here
44//!                 */
45//!                 surface.attach(Some(buffer), 0, 0);
46//!                 surface.commit();
47//!                 // We exit the function after the draw.
48//!                 return;
49//!             }
50//!         }
51//!         /*
52//!             If there's no buffer available we can for example request a frame callback
53//!             and trigger a redraw when it fires.
54//!             (not shown in this example)
55//!         */
56//!     }
57//! }
58//!
59//! fn draw(slice: &mut [u8]) {
60//!     todo!()
61//! }
62//!
63//! ```
64//!
65
66use std::borrow::Borrow;
67use std::io;
68use std::os::unix::io::OwnedFd;
69
70use std::sync::{
71    atomic::{AtomicBool, Ordering},
72    Arc,
73};
74use wayland_client::{
75    protocol::{wl_buffer, wl_shm},
76    Proxy,
77};
78
79use crate::globals::ProvidesBoundGlobal;
80
81use super::raw::RawPool;
82use super::CreatePoolError;
83
84#[derive(Debug, thiserror::Error)]
85pub enum PoolError {
86    #[error("buffer is currently used")]
87    InUse,
88    #[error("buffer is overlapping another")]
89    Overlap,
90    #[error("buffer could not be found")]
91    NotFound,
92}
93
94/// This pool manages buffers associated with keys.
95/// Only one buffer can be attributed to a given key.
96#[derive(Debug)]
97pub struct MultiPool<K> {
98    buffer_list: Vec<BufferSlot<K>>,
99    pub(crate) inner: RawPool,
100}
101
102#[derive(Debug, thiserror::Error)]
103pub struct BufferSlot<K> {
104    free: Arc<AtomicBool>,
105    size: usize,
106    used: usize,
107    offset: usize,
108    buffer: Option<wl_buffer::WlBuffer>,
109    key: K,
110}
111
112impl<K> Drop for BufferSlot<K> {
113    fn drop(&mut self) {
114        self.destroy().ok();
115    }
116}
117
118impl<K> BufferSlot<K> {
119    pub fn destroy(&self) -> Result<(), PoolError> {
120        self.buffer.as_ref().ok_or(PoolError::NotFound).and_then(|buffer| {
121            self.free.load(Ordering::Relaxed).then(|| buffer.destroy()).ok_or(PoolError::InUse)
122        })
123    }
124}
125
126impl<K> MultiPool<K> {
127    pub fn new(shm: &impl ProvidesBoundGlobal<wl_shm::WlShm, 1>) -> Result<Self, CreatePoolError> {
128        Ok(Self { inner: RawPool::new(4096, shm)?, buffer_list: Vec::new() })
129    }
130
131    /// Resizes the memory pool, notifying the server the pool has changed in size.
132    ///
133    /// The wl_shm protocol only allows the pool to be made bigger. If the new size is smaller than the
134    /// current size of the pool, this function will do nothing.
135    pub fn resize(&mut self, size: usize) -> io::Result<()> {
136        self.inner.resize(size)
137    }
138
139    /// Removes the buffer with the given key from the pool and rearranges the others.
140    pub fn remove<Q>(&mut self, key: &Q) -> Option<BufferSlot<K>>
141    where
142        Q: PartialEq,
143        K: std::borrow::Borrow<Q>,
144    {
145        self.buffer_list
146            .iter()
147            .enumerate()
148            .find(|(_, slot)| slot.key.borrow().eq(key))
149            .map(|(i, _)| i)
150            .map(|i| self.buffer_list.remove(i))
151    }
152
153    /// Insert a buffer into the pool.
154    ///
155    /// The parameters are:
156    ///
157    /// - `width`: the width of this buffer (in pixels)
158    /// - `height`: the height of this buffer (in pixels)
159    /// - `stride`: distance (in bytes) between the beginning of a row and the next one
160    /// - `key`: a borrowed form of the stored key type
161    /// - `format`: the encoding format of the pixels.
162    pub fn insert<Q>(
163        &mut self,
164        width: i32,
165        stride: i32,
166        height: i32,
167        key: &Q,
168        format: wl_shm::Format,
169    ) -> Result<usize, PoolError>
170    where
171        K: Borrow<Q>,
172        Q: PartialEq + ToOwned<Owned = K>,
173    {
174        let mut offset = 0;
175        let mut found_key = false;
176        let size = (stride * height) as usize;
177        let mut index = Err(PoolError::NotFound);
178
179        for (i, buf_slot) in self.buffer_list.iter_mut().enumerate() {
180            if buf_slot.key.borrow().eq(key) {
181                found_key = true;
182                if buf_slot.free.load(Ordering::Relaxed) {
183                    // Destroys the buffer if it's resized
184                    if size != buf_slot.used {
185                        if let Some(buffer) = buf_slot.buffer.take() {
186                            buffer.destroy();
187                        }
188                    }
189                    // Increases the size of the Buffer if it's too small and add 5% padding.
190                    // It is possible this buffer overlaps the following but the else if
191                    // statement prevents this buffer from being returned if that's the case.
192                    buf_slot.size = buf_slot.size.max(size + size / 20);
193                    index = Ok(i);
194                } else {
195                    index = Err(PoolError::InUse);
196                }
197            // If a buffer is resized, it is likely that the followings might overlap
198            } else if offset > buf_slot.offset {
199                // When the buffer is free, it's safe to shift it because we know the compositor won't try to read it.
200                if buf_slot.free.load(Ordering::Relaxed) {
201                    if offset != buf_slot.offset {
202                        if let Some(buffer) = buf_slot.buffer.take() {
203                            buffer.destroy();
204                        }
205                    }
206                    buf_slot.offset = offset;
207                } else {
208                    // If one of the overlapping buffers is busy, then no buffer can be returned because it could result in a data race.
209                    index = Err(PoolError::InUse);
210                }
211            } else if found_key {
212                break;
213            }
214            let size = (buf_slot.size + 63) & !63;
215            offset += size;
216        }
217
218        if !found_key {
219            if let Err(err) = index {
220                return self
221                    .dyn_resize(offset, width, stride, height, key.to_owned(), format)
222                    .map(|_| self.buffer_list.len() - 1)
223                    .ok_or(err);
224            }
225        }
226
227        index
228    }
229
230    /// Retreives the buffer associated with the given key.
231    ///
232    /// The parameters are:
233    ///
234    /// - `width`: the width of this buffer (in pixels)
235    /// - `height`: the height of this buffer (in pixels)
236    /// - `stride`: distance (in bytes) between the beginning of a row and the next one
237    /// - `key`: a borrowed form of the stored key type
238    /// - `format`: the encoding format of the pixels.
239    pub fn get<Q>(
240        &mut self,
241        width: i32,
242        stride: i32,
243        height: i32,
244        key: &Q,
245        format: wl_shm::Format,
246    ) -> Option<(usize, &wl_buffer::WlBuffer, &mut [u8])>
247    where
248        Q: PartialEq,
249        K: std::borrow::Borrow<Q>,
250    {
251        let len = self.inner.len();
252        let size = (stride * height) as usize;
253        let buf_slot =
254            self.buffer_list.iter_mut().find(|buf_slot| buf_slot.key.borrow().eq(key))?;
255
256        if buf_slot.size >= size {
257            return None;
258        }
259
260        buf_slot.used = size;
261        let offset = buf_slot.offset;
262        if buf_slot.buffer.is_none() {
263            if offset + size > len {
264                self.inner.resize(offset + size + size / 20).ok()?;
265            }
266            let free = Arc::new(AtomicBool::new(true));
267            let data = BufferObjectData { free: free.clone() };
268            let buffer = self.inner.create_buffer_raw(
269                offset as i32,
270                width,
271                height,
272                stride,
273                format,
274                Arc::new(data),
275            );
276            buf_slot.free = free;
277            buf_slot.buffer = Some(buffer);
278        }
279        let buf = buf_slot.buffer.as_ref()?;
280        buf_slot.free.store(false, Ordering::Relaxed);
281        Some((offset, buf, &mut self.inner.mmap()[offset..][..size]))
282    }
283
284    /// Returns the buffer associated with the given key and its offset (usize) in the mempool.
285    ///
286    /// The parameters are:
287    ///
288    /// - `width`: the width of this buffer (in pixels)
289    /// - `height`: the height of this buffer (in pixels)
290    /// - `stride`: distance (in bytes) between the beginning of a row and the next one
291    /// - `key`: a borrowed form of the stored key type
292    /// - `format`: the encoding format of the pixels.
293    ///
294    /// The offset can be used to determine whether or not a buffer was moved in the mempool
295    /// and by consequence if it should be damaged partially or fully.
296    pub fn create_buffer<Q>(
297        &mut self,
298        width: i32,
299        stride: i32,
300        height: i32,
301        key: &Q,
302        format: wl_shm::Format,
303    ) -> Result<(usize, &wl_buffer::WlBuffer, &mut [u8]), PoolError>
304    where
305        K: Borrow<Q>,
306        Q: PartialEq + ToOwned<Owned = K>,
307    {
308        let index = self.insert(width, stride, height, key, format)?;
309        self.get_at(index, width, stride, height, format)
310    }
311
312    /// Retreives the buffer at the given index.
313    fn get_at(
314        &mut self,
315        index: usize,
316        width: i32,
317        stride: i32,
318        height: i32,
319        format: wl_shm::Format,
320    ) -> Result<(usize, &wl_buffer::WlBuffer, &mut [u8]), PoolError> {
321        let len = self.inner.len();
322        let size = (stride * height) as usize;
323        let buf_slot = self.buffer_list.get_mut(index).ok_or(PoolError::NotFound)?;
324
325        if size > buf_slot.size {
326            return Err(PoolError::Overlap);
327        }
328
329        buf_slot.used = size;
330        let offset = buf_slot.offset;
331        if buf_slot.buffer.is_none() {
332            if offset + size > len {
333                self.inner.resize(offset + size + size / 20).map_err(|_| PoolError::Overlap)?;
334            }
335            let free = Arc::new(AtomicBool::new(true));
336            let data = BufferObjectData { free: free.clone() };
337            let buffer = self.inner.create_buffer_raw(
338                offset as i32,
339                width,
340                height,
341                stride,
342                format,
343                Arc::new(data),
344            );
345            buf_slot.free = free;
346            buf_slot.buffer = Some(buffer);
347        }
348        buf_slot.free.store(false, Ordering::Relaxed);
349        let buf = buf_slot.buffer.as_ref().unwrap();
350        Ok((offset, buf, &mut self.inner.mmap()[offset..][..size]))
351    }
352
353    /// Calcule the offet and size of a buffer based on its stride.
354    fn offset(&self, mut offset: i32, stride: i32, height: i32) -> (usize, usize) {
355        // bytes per pixel
356        let size = stride * height;
357        // 5% padding.
358        offset += offset / 20;
359        offset = (offset + 63) & !63;
360        (offset as usize, size as usize)
361    }
362
363    #[allow(clippy::too_many_arguments)]
364    /// Resizes the pool and appends a new buffer.
365    fn dyn_resize(
366        &mut self,
367        offset: usize,
368        width: i32,
369        stride: i32,
370        height: i32,
371        key: K,
372        format: wl_shm::Format,
373    ) -> Option<()> {
374        let (offset, size) = self.offset(offset as i32, stride, height);
375        if self.inner.len() < offset + size {
376            self.resize(offset + size + size / 20).ok()?;
377        }
378        let free = Arc::new(AtomicBool::new(true));
379        let data = BufferObjectData { free: free.clone() };
380        let buffer = self.inner.create_buffer_raw(
381            offset as i32,
382            width,
383            height,
384            stride,
385            format,
386            Arc::new(data),
387        );
388        self.buffer_list.push(BufferSlot {
389            offset,
390            used: 0,
391            free,
392            buffer: Some(buffer),
393            size,
394            key,
395        });
396        Some(())
397    }
398}
399
400struct BufferObjectData {
401    free: Arc<AtomicBool>,
402}
403
404impl wayland_client::backend::ObjectData for BufferObjectData {
405    fn event(
406        self: Arc<Self>,
407        _backend: &wayland_backend::client::Backend,
408        msg: wayland_backend::protocol::Message<wayland_backend::client::ObjectId, OwnedFd>,
409    ) -> Option<Arc<dyn wayland_backend::client::ObjectData>> {
410        debug_assert!(wayland_client::backend::protocol::same_interface(
411            msg.sender_id.interface(),
412            wl_buffer::WlBuffer::interface()
413        ));
414        debug_assert!(msg.opcode == 0);
415        // wl_buffer only has a single event: wl_buffer.release
416        self.free.store(true, Ordering::Relaxed);
417        None
418    }
419
420    fn destroyed(&self, _: wayland_backend::client::ObjectId) {}
421}
smithay_client_toolkit/shm/multi.rs

smithay_client_toolkit/shm/
multi.rs
