Correctly enumerate audio devices (core + wasapi)

Cargo.toml

@@ -11,6 +11,7 @@ keywords = ["audio", "sound"]
 
 [dependencies]
 libc = "*"
+lazy_static = "0.1"
 
 [target.i686-pc-windows-gnu.dependencies]
 winapi = "0.2.1"

examples/beep.rs

@@ -1,7 +1,7 @@
 extern crate cpal;
 
 fn main() {
-    let mut channel = cpal::Voice::new();
+    let mut channel = cpal::Voice::new(&cpal::get_default_endpoint().unwrap()).unwrap();
 
     // Produce a sinusoid of maximum amplitude.
     let mut data_source = (0u64..).map(|t| t as f32 * 0.03)

src/lib.rs

@@ -28,8 +28,12 @@ reaches the end of the data, it will stop playing. You must continuously fill th
 calling `append_data` repeatedly if you don't want the audio to stop playing.
 
 */
+#[macro_use]
+extern crate lazy_static;
+
 pub use samples_formats::{SampleFormat, Sample};
 
+use std::error::Error;
 use std::ops::{Deref, DerefMut};
 
 mod samples_formats;
@@ -57,6 +61,43 @@ pub type ChannelsCount = u16;
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub struct SamplesRate(pub u32);
 
+/// Describes a format.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub struct Format {
+    pub channels: ChannelsCount,
+    pub samples_rate: SamplesRate,
+    pub data_type: SampleFormat,
+}
+
+/// An iterator for the list of formats that are supported by the backend.
+pub struct EndpointsIterator(cpal_impl::EndpointsIterator);
+
+impl Iterator for EndpointsIterator {
+    type Item = Endpoint;
+
+    fn next(&mut self) -> Option<Endpoint> {
+        self.0.next().map(Endpoint)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+/// Return an iterator to the list of formats that are supported by the system.
+pub fn get_endpoints_list() -> EndpointsIterator {
+    EndpointsIterator(Default::default())
+}
+
+/// Return the default endpoint, or `None` if no device is available.
+pub fn get_default_endpoint() -> Option<Endpoint> {
+    cpal_impl::get_default_endpoint().map(Endpoint)
+}
+
+/// An opaque type that identifies an end point.
+#[derive(Clone, PartialEq, Eq)]
+pub struct Endpoint(cpal_impl::Endpoint);
+
 /// Represents a buffer that must be filled with audio data.
 ///
 /// You should destroy this object as soon as possible. Data is only committed when it
@@ -95,9 +136,9 @@ pub struct Voice(cpal_impl::Voice);
 
 impl Voice {
     /// Builds a new channel.
-    pub fn new() -> Voice {
+    pub fn new(endpoint: &Endpoint) -> Result<Voice, Box<Error>> {
-        let channel = cpal_impl::Voice::new();
+        let channel = try!(cpal_impl::Voice::new(&endpoint.0));
-        Voice(channel)
+        Ok(Voice(channel))
     }
 
     /// Returns the number of channels.

src/wasapi/com.rs

@@ -0,0 +1,32 @@
+//! Handles COM initialization and cleanup.
+
+use std::ptr;
+use super::winapi;
+use super::ole32;
+use super::check_result;
+
+thread_local!(static COM_INITIALIZED: ComInitialized = {
+    unsafe {
+        // this call can fail if another library initialized COM in single-threaded mode
+        // handling this situation properly would make the API more annoying, so we just don't care
+        check_result(ole32::CoInitializeEx(ptr::null_mut(), winapi::COINIT_MULTITHREADED)).unwrap();
+        ComInitialized(ptr::null_mut())
+    }
+});
+
+/// RAII object that guards the fact that COM is initialized.
+///
+// We store a raw pointer because it's the only way at the moment to remove `Send`/`Sync` from the
+// object.
+struct ComInitialized(*mut ());
+
+impl Drop for ComInitialized {
+    fn drop(&mut self) {
+        unsafe { ole32::CoUninitialize() };
+    }
+}
+
+/// Ensures that COM is initialized in this thread.
+pub fn com_initialized() {
+    COM_INITIALIZED.with(|_| {});
+}

src/wasapi/enumerate.rs

@@ -0,0 +1,126 @@
+use super::winapi;
+use super::ole32;
+use super::com;
+use super::Endpoint;
+use super::check_result;
+
+use std::mem;
+use std::ptr;
+
+lazy_static! {
+    static ref ENUMERATOR: Enumerator = {
+        // COM initialization is thread local, but we only need to have COM initialized in the
+        // thread we create the objects in
+        com::com_initialized();
+
+        // building the devices enumerator object
+        unsafe {
+            let mut enumerator: *mut winapi::IMMDeviceEnumerator = mem::uninitialized();
+            
+            let hresult = ole32::CoCreateInstance(&winapi::CLSID_MMDeviceEnumerator,
+                                                  ptr::null_mut(), winapi::CLSCTX_ALL,
+                                                  &winapi::IID_IMMDeviceEnumerator,
+                                                  &mut enumerator
+                                                           as *mut *mut winapi::IMMDeviceEnumerator
+                                                           as *mut _);
+
+            check_result(hresult).unwrap();
+            Enumerator(enumerator)
+        }
+    };
+}
+
+/// RAII object around `winapi::IMMDeviceEnumerator`.
+struct Enumerator(*mut winapi::IMMDeviceEnumerator);
+
+unsafe impl Send for Enumerator {}
+unsafe impl Sync for Enumerator {}
+
+impl Drop for Enumerator {
+    fn drop(&mut self) {
+        unsafe {
+            (*self.0).Release();
+        }
+    }
+}
+
+/// WASAPI implementation for `EndpointsIterator`.
+pub struct EndpointsIterator {
+    collection: *mut winapi::IMMDeviceCollection,
+    total_count: u32,
+    next_item: u32,
+}
+
+unsafe impl Send for EndpointsIterator {}
+unsafe impl Sync for EndpointsIterator {}
+
+impl Drop for EndpointsIterator {
+    fn drop(&mut self) {
+        unsafe {
+            (*self.collection).Release();
+        }
+    }
+}
+
+impl Default for EndpointsIterator {
+    fn default() -> EndpointsIterator {
+        unsafe {
+            let mut collection: *mut winapi::IMMDeviceCollection = mem::uninitialized();
+            // can fail because of wrong parameters (should never happen) or out of memory
+            check_result((*ENUMERATOR.0).EnumAudioEndpoints(winapi::EDataFlow::eRender,
+                                                            winapi::DEVICE_STATE_ACTIVE,
+                                                            &mut collection))
+                                                            .unwrap();
+
+            let mut count = mem::uninitialized();
+            // can fail if the parameter is null, which should never happen
+            check_result((*collection).GetCount(&mut count)).unwrap();
+
+            EndpointsIterator {
+                collection: collection,
+                total_count: count,
+                next_item: 0,
+            }
+        }
+    }
+}
+
+impl Iterator for EndpointsIterator {
+    type Item = Endpoint;
+
+    fn next(&mut self) -> Option<Endpoint> {
+        if self.next_item >= self.total_count {
+            return None;
+        }
+
+        unsafe {
+            let mut device = mem::uninitialized();
+            // can fail if out of range, which we just checked above
+            check_result((*self.collection).Item(self.next_item, &mut device)).unwrap();
+
+            self.next_item += 1;
+            Some(Endpoint(device))
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let num = self.total_count - self.next_item;
+        let num = num as usize;
+        (num, Some(num))
+    }
+}
+
+pub fn get_default_endpoint() -> Option<Endpoint> {
+    unsafe {
+        let mut device = mem::uninitialized();
+        let hres = (*ENUMERATOR.0).GetDefaultAudioEndpoint(winapi::EDataFlow::eRender,
+                                                           winapi::ERole::eConsole, &mut device);
+
+        if let Err(_err) = check_result(hres) {
+            return None;        // TODO: check specifically for `E_NOTFOUND`, and panic otherwise
+        }
+
+        Some(Endpoint(device))
+    }
+}

src/wasapi/mod.rs

@@ -2,255 +2,40 @@ extern crate libc;
 extern crate winapi;
 extern crate ole32;
 
-use std::{cmp, slice, mem, ptr};
+use std::io::Error as IoError;
-use std::marker::PhantomData;
 
-// TODO: determine if should be NoSend or not
+pub use self::enumerate::{EndpointsIterator, get_default_endpoint};
-pub struct Voice {
+pub use self::voice::{Voice, Buffer};
-    audio_client: *mut winapi::IAudioClient,
-    render_client: *mut winapi::IAudioRenderClient,
-    max_frames_in_buffer: winapi::UINT32,
-    num_channels: winapi::WORD,
-    bytes_per_frame: winapi::WORD,
-    samples_per_second: winapi::DWORD,
-    bits_per_sample: winapi::WORD,
-    playing: bool,
-}
 
-pub struct Buffer<'a, T: 'a> {
+mod com;
-    render_client: *mut winapi::IAudioRenderClient,
+mod enumerate;
-    buffer_data: *mut T,
+mod voice;
-    buffer_len: usize,
-    frames: winapi::UINT32,
-    marker: PhantomData<&'a mut T>,
-}
 
-impl Voice {
+/// An opaque type that identifies an end point.
-    pub fn new() -> Voice {
+#[derive(PartialEq, Eq)]
-        init().unwrap()
+#[allow(raw_pointer_derive)]
-    }
+pub struct Endpoint(*mut winapi::IMMDevice);
 
-    pub fn get_channels(&self) -> ::ChannelsCount {
+unsafe impl Send for Endpoint {}
-        self.num_channels as ::ChannelsCount
+unsafe impl Sync for Endpoint {}
-    }
 
-    pub fn get_samples_rate(&self) -> ::SamplesRate {
+impl Clone for Endpoint {
-        ::SamplesRate(self.samples_per_second as u32)
+    fn clone(&self) -> Endpoint {
-    }
+        unsafe { (*self.0).AddRef(); }
-
+        Endpoint(self.0)
-    pub fn get_samples_format(&self) -> ::SampleFormat {
-        match self.bits_per_sample {
-            16 => ::SampleFormat::I16,
-            _ => panic!("{}-bit format not yet supported", self.bits_per_sample),
-        }
-    }
-
-    pub fn append_data<'a, T>(&'a mut self, max_elements: usize) -> Buffer<'a, T> {
-        unsafe {
-            loop {
-                // 
-                let frames_available = {
-                    let mut padding = mem::uninitialized();
-                    let hresult = (*self.audio_client).GetCurrentPadding(&mut padding);
-                    check_result(hresult).unwrap();
-                    self.max_frames_in_buffer - padding
-                };
-
-                if frames_available == 0 {
-                    // TODO: 
-                    ::std::thread::sleep_ms(1);
-                    continue;
-                }
-
-                let frames_available = cmp::min(frames_available,
-                                                max_elements as u32 * mem::size_of::<T>() as u32 /
-                                                self.bytes_per_frame as u32);
-                assert!(frames_available != 0);
-
-                // loading buffer
-                let (buffer_data, buffer_len) = {
-                    let mut buffer: *mut winapi::BYTE = mem::uninitialized();
-                    let hresult = (*self.render_client).GetBuffer(frames_available,
-                                    &mut buffer as *mut *mut libc::c_uchar);
-                    check_result(hresult).unwrap();
-                    assert!(!buffer.is_null());
-
-                    (buffer as *mut T,
-                     frames_available as usize * self.bytes_per_frame as usize
-                          / mem::size_of::<T>())
-                };
-
-                let buffer = Buffer {
-                    render_client: self.render_client,
-                    buffer_data: buffer_data,
-                    buffer_len: buffer_len,
-                    frames: frames_available,
-                    marker: PhantomData,
-                };
-
-                return buffer;
-            }
-        }
-    }
-
-    pub fn play(&mut self) {
-        if !self.playing {
-            unsafe {
-                let hresult = (*self.audio_client).Start();
-                check_result(hresult).unwrap();
-            }
-        }
-
-        self.playing = true;
-    }
-
-    pub fn pause(&mut self) {
-        if self.playing {
-            unsafe {
-                let hresult = (*self.audio_client).Stop();
-                check_result(hresult).unwrap();
-            }
-        }
-
-        self.playing = false;
     }
 }
 
-unsafe impl Send for Voice {}
+impl Drop for Endpoint {
-unsafe impl Sync for Voice {}
-
-impl Drop for Voice {
     fn drop(&mut self) {
-        unsafe {
+        unsafe { (*self.0).Release(); }
-            (*self.render_client).Release();
-            (*self.audio_client).Release();
-        }
     }
 }
 
-impl<'a, T> Buffer<'a, T> {
+fn check_result(result: winapi::HRESULT) -> Result<(), IoError> {
-    pub fn get_buffer<'b>(&'b mut self) -> &'b mut [T] {
-        unsafe {
-            slice::from_raw_parts_mut(self.buffer_data, self.buffer_len)
-        }
-    }
-
-    pub fn finish(self) {
-        // releasing buffer
-        unsafe {
-            let hresult = (*self.render_client).ReleaseBuffer(self.frames as u32, 0);
-            check_result(hresult).unwrap();
-        };
-    }
-}
-
-fn init() -> Result<Voice, String> {
-    // FIXME: release everything
-    unsafe {
-        try!(check_result(ole32::CoInitializeEx(ptr::null_mut(), 0)));
-
-        // building the devices enumerator object
-        let enumerator = {
-            let mut enumerator: *mut winapi::IMMDeviceEnumerator = mem::uninitialized();
-            
-            let hresult = ole32::CoCreateInstance(&winapi::CLSID_MMDeviceEnumerator,
-                                                   ptr::null_mut(), winapi::CLSCTX_ALL,
-                                                   &winapi::IID_IMMDeviceEnumerator,
-                                                   mem::transmute(&mut enumerator));
-
-            try!(check_result(hresult));
-            &mut *enumerator
-        };
-
-        // getting the default end-point
-        let device = {
-            let mut device: *mut winapi::IMMDevice = mem::uninitialized();
-            let hresult = enumerator.GetDefaultAudioEndpoint(winapi::EDataFlow::eRender, winapi::ERole::eConsole,
-                            mem::transmute(&mut device));
-            try!(check_result(hresult));
-            &mut *device
-        };
-
-        // activating in order to get a `IAudioClient`
-        let audio_client: &mut winapi::IAudioClient = {
-            let mut audio_client: *mut winapi::IAudioClient = mem::uninitialized();
-            let hresult = device.Activate(&winapi::IID_IAudioClient, winapi::CLSCTX_ALL,
-                            ptr::null_mut(), mem::transmute(&mut audio_client));
-            try!(check_result(hresult));
-            &mut *audio_client
-        };
-
-        // computing the format and initializing the device
-        let format = {
-            let format_attempt = winapi::WAVEFORMATEX {
-                wFormatTag: 1,      // WAVE_FORMAT_PCM ; TODO: replace by constant
-                nChannels: 2,
-                nSamplesPerSec: 44100,
-                nAvgBytesPerSec: 2 * 44100 * 2,
-                nBlockAlign: (2 * 16) / 8,
-                wBitsPerSample: 16,
-                cbSize: 0,
-            };
-
-            let mut format_ptr: *mut winapi::WAVEFORMATEX = mem::uninitialized();
-            let hresult = audio_client.IsFormatSupported(winapi::AUDCLNT_SHAREMODE::AUDCLNT_SHAREMODE_SHARED,
-                            &format_attempt, &mut format_ptr);
-            try!(check_result(hresult));
-
-            let format = if format_ptr.is_null() {
-                &format_attempt
-            } else {
-                &*format_ptr
-            };
-
-            let format_copy = ptr::read(format);
-
-            let hresult = audio_client.Initialize(winapi::AUDCLNT_SHAREMODE::AUDCLNT_SHAREMODE_SHARED,
-                            0, 10000000, 0, format, ptr::null());
-
-            if !format_ptr.is_null() {
-                ole32::CoTaskMemFree(format_ptr as *mut _);
-            }
-
-            try!(check_result(hresult));
-
-            format_copy
-        };
-
-        // 
-        let max_frames_in_buffer = {
-            let mut max_frames_in_buffer = mem::uninitialized();
-            let hresult = audio_client.GetBufferSize(&mut max_frames_in_buffer);
-            try!(check_result(hresult));
-            max_frames_in_buffer
-        };
-
-        // 
-        let render_client = {
-            let mut render_client: *mut winapi::IAudioRenderClient = mem::uninitialized();
-            let hresult = audio_client.GetService(&winapi::IID_IAudioRenderClient,
-                            mem::transmute(&mut render_client));
-            try!(check_result(hresult));
-            &mut *render_client
-        };
-
-        Ok(Voice {
-            audio_client: audio_client,
-            render_client: render_client,
-            max_frames_in_buffer: max_frames_in_buffer,
-            num_channels: format.nChannels,
-            bytes_per_frame: format.nBlockAlign,
-            samples_per_second: format.nSamplesPerSec,
-            bits_per_sample: format.wBitsPerSample,
-            playing: false,
-        })
-    }
-}
-
-fn check_result(result: winapi::HRESULT) -> Result<(), String> {
     if result < 0 {
-        return Err(format!("Error in winapi call"));        // TODO: 
+        Err(IoError::from_raw_os_error(result))
+    } else {
+        Ok(())
     }
-
-    Ok(())
 }

src/wasapi/voice.rs

@@ -0,0 +1,231 @@
+use super::com;
+use super::ole32;
+use super::winapi;
+use super::Endpoint;
+use super::check_result;
+
+use std::io::Error as IoError;
+use std::cmp;
+use std::slice;
+use std::mem;
+use std::ptr;
+use std::marker::PhantomData;
+
+pub struct Voice {
+    audio_client: *mut winapi::IAudioClient,
+    render_client: *mut winapi::IAudioRenderClient,
+    max_frames_in_buffer: winapi::UINT32,
+    num_channels: winapi::WORD,
+    bytes_per_frame: winapi::WORD,
+    samples_per_second: winapi::DWORD,
+    bits_per_sample: winapi::WORD,
+    playing: bool,
+}
+
+unsafe impl Send for Voice {}
+unsafe impl Sync for Voice {}
+
+impl Voice {
+    pub fn new(end_point: &Endpoint) -> Result<Voice, IoError> {
+        // FIXME: release everything
+        unsafe {
+            // making sure that COM is initialized
+            // it's not actually sure that this is required, but when in doubt do it
+            com::com_initialized();
+
+            // activating the end point in order to get a `IAudioClient`
+            let audio_client: *mut winapi::IAudioClient = {
+                let mut audio_client = mem::uninitialized();
+                let hresult = (*end_point.0).Activate(&winapi::IID_IAudioClient, winapi::CLSCTX_ALL,
+                                                      ptr::null_mut(), &mut audio_client);
+                // can fail if the device has been disconnected since we enumerated it, or if
+                // the device doesn't support playback for some reason
+                try!(check_result(hresult));
+                audio_client as *mut _
+            };
+
+            // computing the format and initializing the device
+            let format = {
+                let format_attempt = winapi::WAVEFORMATEX {
+                    wFormatTag: 1,      // WAVE_FORMAT_PCM ; TODO: replace by constant
+                    nChannels: 2,
+                    nSamplesPerSec: 44100,
+                    nAvgBytesPerSec: 2 * 44100 * 2,
+                    nBlockAlign: (2 * 16) / 8,
+                    wBitsPerSample: 16,
+                    cbSize: 0,
+                };
+
+                let mut format_ptr: *mut winapi::WAVEFORMATEX = mem::uninitialized();
+                let hresult = (*audio_client).IsFormatSupported(winapi::AUDCLNT_SHAREMODE::AUDCLNT_SHAREMODE_SHARED,
+                                                             &format_attempt, &mut format_ptr);
+                try!(check_result(hresult));
+
+                let format = if format_ptr.is_null() {
+                    &format_attempt
+                } else {
+                    &*format_ptr
+                };
+
+                let format_copy = ptr::read(format);
+
+                let hresult = (*audio_client).Initialize(winapi::AUDCLNT_SHAREMODE::AUDCLNT_SHAREMODE_SHARED,
+                                0, 10000000, 0, format, ptr::null());
+
+                if !format_ptr.is_null() {
+                    ole32::CoTaskMemFree(format_ptr as *mut _);
+                }
+
+                try!(check_result(hresult));
+
+                format_copy
+            };
+
+            // 
+            let max_frames_in_buffer = {
+                let mut max_frames_in_buffer = mem::uninitialized();
+                let hresult = (*audio_client).GetBufferSize(&mut max_frames_in_buffer);
+                try!(check_result(hresult));
+                max_frames_in_buffer
+            };
+
+            // 
+            let render_client = {
+                let mut render_client: *mut winapi::IAudioRenderClient = mem::uninitialized();
+                let hresult = (*audio_client).GetService(&winapi::IID_IAudioRenderClient,
+                                mem::transmute(&mut render_client));
+                try!(check_result(hresult));
+                &mut *render_client
+            };
+
+            Ok(Voice {
+                audio_client: audio_client,
+                render_client: render_client,
+                max_frames_in_buffer: max_frames_in_buffer,
+                num_channels: format.nChannels,
+                bytes_per_frame: format.nBlockAlign,
+                samples_per_second: format.nSamplesPerSec,
+                bits_per_sample: format.wBitsPerSample,
+                playing: false,
+            })
+        }
+    }
+
+    pub fn get_channels(&self) -> ::ChannelsCount {
+        self.num_channels as ::ChannelsCount
+    }
+
+    pub fn get_samples_rate(&self) -> ::SamplesRate {
+        ::SamplesRate(self.samples_per_second as u32)
+    }
+
+    pub fn get_samples_format(&self) -> ::SampleFormat {
+        match self.bits_per_sample {
+            16 => ::SampleFormat::I16,
+            _ => panic!("{}-bit format not yet supported", self.bits_per_sample),
+        }
+    }
+
+    pub fn append_data<'a, T>(&'a mut self, max_elements: usize) -> Buffer<'a, T> {
+        unsafe {
+            loop {
+                // 
+                let frames_available = {
+                    let mut padding = mem::uninitialized();
+                    let hresult = (*self.audio_client).GetCurrentPadding(&mut padding);
+                    check_result(hresult).unwrap();
+                    self.max_frames_in_buffer - padding
+                };
+
+                if frames_available == 0 {
+                    // TODO: 
+                    ::std::thread::sleep_ms(1);
+                    continue;
+                }
+
+                let frames_available = cmp::min(frames_available,
+                                                max_elements as u32 * mem::size_of::<T>() as u32 /
+                                                self.bytes_per_frame as u32);
+                assert!(frames_available != 0);
+
+                // loading buffer
+                let (buffer_data, buffer_len) = {
+                    let mut buffer: *mut winapi::BYTE = mem::uninitialized();
+                    let hresult = (*self.render_client).GetBuffer(frames_available,
+                                    &mut buffer as *mut *mut _);
+                    check_result(hresult).unwrap();
+                    assert!(!buffer.is_null());
+
+                    (buffer as *mut T,
+                     frames_available as usize * self.bytes_per_frame as usize
+                          / mem::size_of::<T>())
+                };
+
+                let buffer = Buffer {
+                    render_client: self.render_client,
+                    buffer_data: buffer_data,
+                    buffer_len: buffer_len,
+                    frames: frames_available,
+                    marker: PhantomData,
+                };
+
+                return buffer;
+            }
+        }
+    }
+
+    pub fn play(&mut self) {
+        if !self.playing {
+            unsafe {
+                let hresult = (*self.audio_client).Start();
+                check_result(hresult).unwrap();
+            }
+        }
+
+        self.playing = true;
+    }
+
+    pub fn pause(&mut self) {
+        if self.playing {
+            unsafe {
+                let hresult = (*self.audio_client).Stop();
+                check_result(hresult).unwrap();
+            }
+        }
+
+        self.playing = false;
+    }
+}
+
+impl Drop for Voice {
+    fn drop(&mut self) {
+        unsafe {
+            (*self.render_client).Release();
+            (*self.audio_client).Release();
+        }
+    }
+}
+
+pub struct Buffer<'a, T: 'a> {
+    render_client: *mut winapi::IAudioRenderClient,
+    buffer_data: *mut T,
+    buffer_len: usize,
+    frames: winapi::UINT32,
+    marker: PhantomData<&'a mut T>,
+}
+
+impl<'a, T> Buffer<'a, T> {
+    pub fn get_buffer<'b>(&'b mut self) -> &'b mut [T] {
+        unsafe {
+            slice::from_raw_parts_mut(self.buffer_data, self.buffer_len)
+        }
+    }
+
+    pub fn finish(self) {
+        // releasing buffer
+        unsafe {
+            let hresult = (*self.render_client).ReleaseBuffer(self.frames as u32, 0);
+            check_result(hresult).unwrap();
+        };
+    }
+}