Convert shadow sample to map_async

.gitignore

@@ -2,4 +2,5 @@
 **/*.rs.bk
 #Cargo.lock
 .vscode
+.vs
 build

examples/hello_compute_rust/main.rs

@@ -4,14 +4,6 @@ extern crate wgpu_native;
 
 use std::str::FromStr;
 
-// TODO: deduplicate this with the copy in gfx-examples/framework
-pub fn cast_slice<T>(data: &[T]) -> &[u8] {
-    use std::mem::size_of;
-    use std::slice::from_raw_parts;
-
-    unsafe { from_raw_parts(data.as_ptr() as *const u8, data.len() * size_of::<T>()) }
-}
-
 fn main() {
     env_logger::init();
 
@@ -39,16 +31,17 @@ fn main() {
     let cs_bytes = include_bytes!("./../data/collatz.comp.spv");
     let cs_module = device.create_shader_module(cs_bytes);
 
-    let staging_buffer = device.create_buffer(&wgpu::BufferDescriptor {
+    let staging_buffer = device
-        size,
+        .create_buffer_mapped(
-        usage: wgpu::BufferUsageFlags::MAP_READ
+            numbers.len(),
-            | wgpu::BufferUsageFlags::TRANSFER_DST
+            wgpu::BufferUsageFlags::MAP_READ
-            | wgpu::BufferUsageFlags::TRANSFER_SRC,
+                | wgpu::BufferUsageFlags::TRANSFER_DST
-    });
+                | wgpu::BufferUsageFlags::TRANSFER_SRC,
-    staging_buffer.set_sub_data(0, cast_slice(&numbers));
+        )
+        .fill_from_slice(&numbers);
 
     let storage_buffer = device.create_buffer(&wgpu::BufferDescriptor {
-        size: (numbers.len() * std::mem::size_of::<u32>()) as u32,
+        size,
         usage: wgpu::BufferUsageFlags::STORAGE
             | wgpu::BufferUsageFlags::TRANSFER_DST
             | wgpu::BufferUsageFlags::TRANSFER_SRC,
@@ -68,7 +61,7 @@ fn main() {
             binding: 0,
             resource: wgpu::BindingResource::Buffer {
                 buffer: &storage_buffer,
-                range: 0..(numbers.len() as u32),
+                range: 0..size,
             },
         }],
     });
@@ -95,7 +88,6 @@ fn main() {
     }
     encoder.copy_buffer_to_buffer(&storage_buffer, 0, &staging_buffer, 0, size);
 
-
     staging_buffer.map_read_async(0, size, |result: wgpu::BufferMapAsyncResult<&[u32]>| {
         if let wgpu::BufferMapAsyncResult::Success(data) = result {
             println!("Times: {:?}", data);

gfx-examples/src/cube.rs

@@ -3,14 +3,14 @@ mod framework;
 
 #[derive(Clone, Copy)]
 struct Vertex {
-    pos: [f32; 4],
+    _pos: [f32; 4],
-    tex_coord: [f32; 2],
+    _tex_coord: [f32; 2],
 }
 
 fn vertex(pos: [i8; 3], tc: [i8; 2]) -> Vertex {
     Vertex {
-        pos: [pos[0] as f32, pos[1] as f32, pos[2] as f32, 1.0],
+        _pos: [pos[0] as f32, pos[1] as f32, pos[2] as f32, 1.0],
-        tex_coord: [tc[0] as f32, tc[1] as f32],
+        _tex_coord: [tc[0] as f32, tc[1] as f32],
     }
 }
 
@@ -115,27 +115,13 @@ impl framework::Example for Example {
         // Create the vertex and index buffers
         let vertex_size = mem::size_of::<Vertex>();
         let (vertex_data, index_data) = create_vertices();
-        let vertex_buffer_length = vertex_data.len() * vertex_size;
+        let vertex_buf =
-        let index_buffer_length = index_data.len() * mem::size_of::<u16>();
+            device.create_buffer_mapped(vertex_data.len(), wgpu::BufferUsageFlags::VERTEX)
-        let vertex_buf = {
+            .fill_from_slice(&vertex_data);
-            let (vertex_buf, vertex_buf_data) = device.create_buffer_mapped(&wgpu::BufferDescriptor {
-                size: vertex_buffer_length as u32,
-                usage: wgpu::BufferUsageFlags::VERTEX | wgpu::BufferUsageFlags::TRANSFER_DST | wgpu::BufferUsageFlags::MAP_WRITE,
-            });
-            vertex_buf_data.copy_from_slice(&vertex_data);
-            vertex_buf.unmap();
-            vertex_buf
-        };
 
-        let index_buf = {
+        let index_buf =
-            let (index_buf, index_buf_data) = device.create_buffer_mapped(&wgpu::BufferDescriptor {
+            device.create_buffer_mapped(index_data.len(), wgpu::BufferUsageFlags::INDEX)
-                size: index_buffer_length as u32,
+            .fill_from_slice(&index_data);
-                usage: wgpu::BufferUsageFlags::INDEX | wgpu::BufferUsageFlags::TRANSFER_DST | wgpu::BufferUsageFlags::MAP_WRITE,
-            });
-            index_buf_data.copy_from_slice(&index_data);
-            index_buf.unmap();
-            index_buf
-        };
 
         // Create pipeline layout
         let bind_group_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
@@ -177,15 +163,9 @@ impl framework::Example for Example {
             usage: wgpu::TextureUsageFlags::SAMPLED | wgpu::TextureUsageFlags::TRANSFER_DST,
         });
         let texture_view = texture.create_default_view();
-        let temp_buf = {
+        let temp_buf =
-            let (temp_buf, temp_buf_data) = device.create_buffer_mapped(&wgpu::BufferDescriptor {
+            device.create_buffer_mapped(texels.len(), wgpu::BufferUsageFlags::TRANSFER_SRC)
-                size: texels.len() as u32,
+            .fill_from_slice(&texels);
-                usage: wgpu::BufferUsageFlags::TRANSFER_SRC | wgpu::BufferUsageFlags::TRANSFER_DST | wgpu::BufferUsageFlags::MAP_WRITE,
-            });
-            temp_buf_data.copy_from_slice(&texels);
-            temp_buf.unmap();
-            temp_buf
-        };
         init_encoder.copy_buffer_to_texture(
             wgpu::BufferCopyView {
                 buffer: &temp_buf,
@@ -222,15 +202,9 @@ impl framework::Example for Example {
         });
         let mx_total = Self::generate_matrix(sc_desc.width as f32 / sc_desc.height as f32);
         let mx_ref: &[f32; 16] = mx_total.as_ref();
-        let uniform_buf = {
+        let uniform_buf =
-            let (uniform_buf, uniform_buf_data) = device.create_buffer_mapped(&wgpu::BufferDescriptor {
+            device.create_buffer_mapped(16, wgpu::BufferUsageFlags::UNIFORM | wgpu::BufferUsageFlags::TRANSFER_DST)
-                size: 64,
+            .fill_from_slice(mx_ref);
-                usage: wgpu::BufferUsageFlags::UNIFORM | wgpu::BufferUsageFlags::TRANSFER_DST | wgpu::BufferUsageFlags::MAP_WRITE,
-            });
-            uniform_buf_data.copy_from_slice(mx_ref);
-            uniform_buf.unmap();
-            uniform_buf
-        };
 
         // Create bind group
         let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
@@ -326,17 +300,17 @@ impl framework::Example for Example {
         //empty
     }
 
-    fn resize(&mut self, sc_desc: &wgpu::SwapChainDescriptor, _device: &mut wgpu::Device) {
+    fn resize(&mut self, sc_desc: &wgpu::SwapChainDescriptor, device: &mut wgpu::Device) {
         let mx_total = Self::generate_matrix(sc_desc.width as f32 / sc_desc.height as f32);
         let mx_ref: &[f32; 16] = mx_total.as_ref();
-        // self.uniform_buf.set_sub_data(0, framework::cast_slice(&mx_ref[..]));
-        self.uniform_buf.map_write_async(0, 64, |result: wgpu::BufferMapAsyncResult<&mut [f32]>| {
-            if let wgpu::BufferMapAsyncResult::Success(data) = result {
-                data.copy_from_slice(mx_ref);
-            }
 
-            self.uniform_buf.unmap();
+        let temp_buf =
-        });
+            device.create_buffer_mapped(16, wgpu::BufferUsageFlags::TRANSFER_SRC)
+            .fill_from_slice(mx_ref);
+
+        let mut encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { todo: 0 });
+        encoder.copy_buffer_to_buffer(&temp_buf, 0, &self.uniform_buf, 0, 64);
+        device.get_queue().submit(&[encoder.finish()]);
     }
 
     fn render(&mut self, frame: &wgpu::SwapChainOutput, device: &mut wgpu::Device) {

gfx-examples/src/shadow.rs

@@ -5,16 +5,16 @@ use std::rc::Rc;
 mod framework;
 
 
-#[derive(Clone)]
+#[derive(Clone, Copy)]
 struct Vertex {
-    pos: [i8; 4],
+    _pos: [i8; 4],
-    normal: [i8; 4],
+    _normal: [i8; 4],
 }
 
 fn vertex(pos: [i8; 3], nor: [i8; 3]) -> Vertex {
     Vertex {
-        pos: [pos[0], pos[1], pos[2], 1],
+        _pos: [pos[0], pos[1], pos[2], 1],
-        normal: [nor[0], nor[1], nor[2], 0],
+        _normal: [nor[0], nor[1], nor[2], 0],
     }
 }
 
@@ -101,6 +101,7 @@ struct Light {
 }
 
 #[repr(C)]
+#[derive(Clone, Copy)]
 struct LightRaw {
     proj: [[f32; 4]; 4],
     pos: [f32; 4],
@@ -132,14 +133,16 @@ impl Light {
 }
 
 #[repr(C)]
+#[derive(Clone, Copy)]
 struct ForwardUniforms {
     proj: [[f32; 4]; 4],
     num_lights: [u32; 4],
 }
 
 #[repr(C)]
+#[derive(Clone, Copy)]
 struct EntityUniforms {
-    model: [[f32; 4]; 4],
+    model: cgmath::Matrix4<f32>,
     color: [f32; 4],
 }
 
@@ -190,28 +193,25 @@ impl framework::Example for Example {
         // Create the vertex and index buffers
         let vertex_size = mem::size_of::<Vertex>();
         let (cube_vertex_data, cube_index_data) = create_cube();
-        let cube_vertex_buf = Rc::new(device.create_buffer(&wgpu::BufferDescriptor {
+        let cube_vertex_buf = Rc::new(
-            size: (cube_vertex_data.len() * vertex_size) as u32,
+            device.create_buffer_mapped(cube_vertex_data.len(), wgpu::BufferUsageFlags::VERTEX)
-            usage: wgpu::BufferUsageFlags::VERTEX | wgpu::BufferUsageFlags::TRANSFER_DST,
+            .fill_from_slice(&cube_vertex_data)
-        }));
+        );
-        cube_vertex_buf.set_sub_data(0, framework::cast_slice(&cube_vertex_data));
+
-        let cube_index_buf = Rc::new(device.create_buffer(&wgpu::BufferDescriptor {
+        let cube_index_buf = Rc::new(
-            size: (cube_index_data.len() * 2) as u32,
+            device.create_buffer_mapped(cube_index_data.len(), wgpu::BufferUsageFlags::INDEX)
-            usage: wgpu::BufferUsageFlags::INDEX | wgpu::BufferUsageFlags::TRANSFER_DST,
+            .fill_from_slice(&cube_index_data)
-        }));
+        );
-        cube_index_buf.set_sub_data(0, framework::cast_slice(&cube_index_data));
 
         let (plane_vertex_data, plane_index_data) = create_plane(7);
-        let plane_vertex_buf = device.create_buffer(&wgpu::BufferDescriptor {
+        let plane_vertex_buf =
-            size: (plane_vertex_data.len() * vertex_size) as u32,
+            device.create_buffer_mapped(plane_vertex_data.len(), wgpu::BufferUsageFlags::VERTEX)
-            usage: wgpu::BufferUsageFlags::VERTEX | wgpu::BufferUsageFlags::TRANSFER_DST,
+            .fill_from_slice(&plane_vertex_data);
-        });
+
-        plane_vertex_buf.set_sub_data(0, framework::cast_slice(&plane_vertex_data));
+        let plane_index_buf =
-        let plane_index_buf = device.create_buffer(&wgpu::BufferDescriptor {
+            device.create_buffer_mapped(plane_index_data.len(), wgpu::BufferUsageFlags::INDEX)
-            size: (plane_index_data.len() * 2) as u32,
+            .fill_from_slice(&plane_index_data);
-            usage: wgpu::BufferUsageFlags::INDEX | wgpu::BufferUsageFlags::TRANSFER_DST,
+
-        });
-        plane_index_buf.set_sub_data(0, framework::cast_slice(&plane_index_data));
         let entity_uniform_size = mem::size_of::<EntityUniforms>() as u32;
         let plane_uniform_buf = device.create_buffer(&wgpu::BufferDescriptor {
             size: entity_uniform_size,
@@ -517,17 +517,15 @@ impl framework::Example for Example {
                 ],
             });
 
-            let uniform_size = mem::size_of::<ForwardUniforms>() as u32;
-            let uniform_buf = device.create_buffer(&wgpu::BufferDescriptor {
-                size: uniform_size,
-                usage: wgpu::BufferUsageFlags::UNIFORM | wgpu::BufferUsageFlags::TRANSFER_DST,
-            });
             let mx_total = Self::generate_matrix(sc_desc.width as f32 / sc_desc.height as f32);
-            let data = ForwardUniforms {
+            let forward_uniforms = ForwardUniforms {
                 proj: *mx_total.as_ref(),
                 num_lights: [lights.len() as u32, 0, 0, 0],
             };
-            uniform_buf.set_sub_data(0, framework::cast_slice(&[data]));
+            let uniform_size = mem::size_of::<ForwardUniforms>() as u32;
+            let uniform_buf =
+                device.create_buffer_mapped(1, wgpu::BufferUsageFlags::UNIFORM | wgpu::BufferUsageFlags::TRANSFER_DST)
+                .fill_from_slice(&[forward_uniforms]);
 
             // Create bind group
             let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
@@ -639,9 +637,17 @@ impl framework::Example for Example {
     }
 
     fn resize(&mut self, sc_desc: &wgpu::SwapChainDescriptor, device: &mut wgpu::Device) {
-        let mx_total = Self::generate_matrix(sc_desc.width as f32 / sc_desc.height as f32);
+        {
-        let mx_ref: &[f32; 16] = mx_total.as_ref();
+            let mx_total = Self::generate_matrix(sc_desc.width as f32 / sc_desc.height as f32);
-        self.forward_pass.uniform_buf.set_sub_data(0, framework::cast_slice(&mx_ref[..]));
+            let mx_ref: &[f32; 16] = mx_total.as_ref();
+            let temp_buf =
+                device.create_buffer_mapped(16, wgpu::BufferUsageFlags::TRANSFER_SRC)
+                .fill_from_slice(mx_ref);
+
+            let mut encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { todo: 0 });
+            encoder.copy_buffer_to_buffer(&temp_buf, 0, &self.forward_pass.uniform_buf, 0, 64);
+            device.get_queue().submit(&[encoder.finish()]);
+        }
 
         let depth_texture = device.create_texture(&wgpu::TextureDescriptor {
             size: wgpu::Extent3d {
@@ -658,28 +664,42 @@ impl framework::Example for Example {
     }
 
     fn render(&mut self, frame: &wgpu::SwapChainOutput, device: &mut wgpu::Device) {
-        for entity in &mut self.entities {
-            if entity.rotation_speed != 0.0 {
-                let rotation = cgmath::Matrix4::from_angle_x(cgmath::Deg(entity.rotation_speed));
-                entity.mx_world = entity.mx_world * rotation;
-            }
-            let data = EntityUniforms {
-                model: *entity.mx_world.as_ref(),
-                color: [entity.color.r, entity.color.g, entity.color.b, entity.color.a],
-            };
-            entity.uniform_buf.set_sub_data(0, framework::cast_slice(&[data]));
-        }
-        if self.lights_are_dirty {
-            self.lights_are_dirty = false;
-            let raw = self.lights
-                .iter()
-                .map(|light| light.to_raw())
-                .collect::<Vec<_>>();
-            self.light_uniform_buf.set_sub_data(0, framework::cast_slice(&raw));
-        }
-
         let mut encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { todo: 0 });
 
+        {
+            let size = mem::size_of::<EntityUniforms>() as u32;
+            let temp_buf_data =
+                device.create_buffer_mapped(self.entities.len(), wgpu::BufferUsageFlags::TRANSFER_SRC);
+
+            for (i, entity) in self.entities.iter_mut().enumerate() {
+                if entity.rotation_speed != 0.0 {
+                    let rotation = cgmath::Matrix4::from_angle_x(cgmath::Deg(entity.rotation_speed));
+                    entity.mx_world = entity.mx_world * rotation;
+                }
+                temp_buf_data.data[i] = EntityUniforms {
+                    model: entity.mx_world.clone(),
+                    color: [entity.color.r, entity.color.g, entity.color.b, entity.color.a],
+                };
+            }
+
+            let temp_buf = temp_buf_data.finish();
+
+            for (i, entity) in self.entities.iter().enumerate() {
+                encoder.copy_buffer_to_buffer(&temp_buf, i as u32 * size, &entity.uniform_buf, 0, size);
+            }
+        }
+
+        if self.lights_are_dirty {
+            self.lights_are_dirty = false;
+            let size = (self.lights.len() * mem::size_of::<LightRaw>()) as u32;
+            let temp_buf_data =
+                device.create_buffer_mapped(self.lights.len(), wgpu::BufferUsageFlags::TRANSFER_SRC);
+            for (i, light) in self.lights.iter().enumerate() {
+                temp_buf_data.data[i] = light.to_raw();
+            }
+            encoder.copy_buffer_to_buffer(&temp_buf_data.finish(), 0, &self.light_uniform_buf, 0, size);
+        }
+        
         for (i, light) in self.lights.iter().enumerate() {
             // The light uniform buffer already has the projection,
             // let's just copy it over to the shadow uniform buffer.

wgpu-native/src/device.rs

@@ -277,27 +277,25 @@ impl DestroyedResources<back::Backend> {
             let mut operation = None;
             let (result, ptr) = {
                 let mut buffer_guard = HUB.buffers.write();
-                let buffer = &mut buffer_guard[buffer_id];
+                let mut buffer = &mut buffer_guard[buffer_id];
                 std::mem::swap(&mut operation, &mut buffer.pending_map_operation);
                 match operation.clone().unwrap() {
                     BufferMapOperation::Read(range, ..) => {
-                        if let Ok(ptr) = unsafe { raw.map_memory(&buffer.memory, range.clone()) } {
+                        match map_buffer(raw, &mut buffer, range.clone(), true, false) {
-                            if !buffer.memory_properties.contains(hal::memory::Properties::COHERENT) {
+                            Ok(ptr) => (BufferMapAsyncStatus::Success, Some(ptr)),
-                                unsafe { raw.invalidate_mapped_memory_ranges(iter::once((&buffer.memory, range.clone()))).unwrap()  }; // TODO
+                            Err(e) => {
+                                log::error!("failed to map buffer for reading: {}", e);
+                                (BufferMapAsyncStatus::Error, None)
                             }
-                            (BufferMapAsyncStatus::Success, Some(ptr))
-                        } else {
-                            (BufferMapAsyncStatus::Error, None)
                         }
                     },
                     BufferMapOperation::Write(range, ..) => {
-                        if let Ok(ptr) = unsafe { raw.map_memory(&buffer.memory, range.clone()) } {
+                        match map_buffer(raw, &mut buffer, range.clone(), false, true) {
-                            if !buffer.memory_properties.contains(hal::memory::Properties::COHERENT) {
+                            Ok(ptr) => (BufferMapAsyncStatus::Success, Some(ptr)),
-                                buffer.mapped_write_ranges.push(range.clone());
+                            Err(e) => {
+                                log::error!("failed to map buffer for writing: {}", e);
+                                (BufferMapAsyncStatus::Error, None)
                             }
-                            (BufferMapAsyncStatus::Success, Some(ptr))
-                        } else {
-                            (BufferMapAsyncStatus::Error, None)
                         }
                     },
                 }
@@ -311,6 +309,23 @@ impl DestroyedResources<back::Backend> {
     }
 }
 
+fn map_buffer(
+    raw: &<back::Backend as hal::Backend>::Device,
+    buffer: &mut resource::Buffer<back::Backend>,
+    range: std::ops::Range<u64>,
+    read: bool,
+    write: bool,
+) -> Result<*mut u8, hal::mapping::Error> {
+    let pointer = unsafe { raw.map_memory(&buffer.memory, range.clone()) }?;
+    if read && !buffer.memory_properties.contains(hal::memory::Properties::COHERENT) {
+        unsafe { raw.invalidate_mapped_memory_ranges(iter::once((&buffer.memory, range.clone()))).unwrap()  }; // TODO
+    }
+    if write && !buffer.memory_properties.contains(hal::memory::Properties::COHERENT) {
+        buffer.mapped_write_ranges.push(range.clone());
+    }
+    Ok(pointer)
+}
+
 pub struct Device<B: hal::Backend> {
     pub(crate) raw: B::Device,
     adapter_id: AdapterId,
@@ -502,19 +517,24 @@ pub extern "C" fn wgpu_device_create_buffer_mapped(
     desc: &resource::BufferDescriptor,
     mapped_ptr_out: *mut *mut u8
 ) -> BufferId {
-    let buffer = device_create_buffer(device_id, desc);
+    let mut desc = desc.clone();
+    desc.usage |= resource::BufferUsageFlags::MAP_WRITE;
+    let mut buffer = device_create_buffer(device_id, &desc);
 
     let device_guard = HUB.devices.read();
     let device = &device_guard[device_id];
 
-    if let Ok(ptr) = unsafe { device.raw.map_memory(&buffer.memory, 0..(desc.size as u64)) } {
+    match map_buffer(&device.raw, &mut buffer, 0..(desc.size as u64), false, true) {
-        unsafe{ *mapped_ptr_out = ptr; }    
+        Ok(ptr) => unsafe { *mapped_ptr_out = ptr; }
+        Err(e) => {
+            log::error!("failed to create buffer in a mapped state: {}", e);
+            unsafe { *mapped_ptr_out = std::ptr::null_mut(); }
+        }
     }
 
     let ref_count = buffer.life_guard.ref_count.clone();
     let id = HUB.buffers.register_local(buffer);
     device_track_buffer(device_id, id, ref_count, resource::BufferUsageFlags::MAP_WRITE);
-
     id
 }
 

wgpu-native/src/resource.rs

@@ -28,6 +28,7 @@ bitflags! {
 }
 
 #[repr(C)]
+#[derive(Clone)]
 pub struct BufferDescriptor {
     pub size: u32,
     pub usage: BufferUsageFlags,

wgpu-rs/src/lib.rs

@@ -233,6 +233,25 @@ impl<'a> TextureCopyView<'a> {
     }
 }
 
+pub struct CreateBufferMapped<'a, T> {
+    id: wgn::BufferId,
+    pub data: &'a mut [T],
+}
+
+impl<'a, T> CreateBufferMapped<'a, T>
+        where T: Copy {
+    pub fn fill_from_slice(self, slice: &[T]) -> Buffer {
+        self.data.copy_from_slice(slice);
+        self.finish()
+    }
+
+    pub fn finish(self) -> Buffer {
+        wgn::wgpu_buffer_unmap(self.id);
+        Buffer {
+            id: self.id,
+        }
+    }
+}
 
 impl Instance {
     pub fn new() -> Self {
@@ -432,21 +451,22 @@ impl Device {
         }
     }
 
-    pub fn create_buffer_mapped<T>(&self, desc: &BufferDescriptor) -> (Buffer, &mut [T])
+    pub fn create_buffer_mapped<'a, T>(&self, count: usize, usage: BufferUsageFlags) -> CreateBufferMapped<'a, T>
             where T: 'static + Copy {
         let type_size = std::mem::size_of::<T>() as u32;
         assert_ne!(type_size, 0);
-        assert_eq!(desc.size % type_size, 0);
 
+        let desc = BufferDescriptor{
+            size: type_size * count as u32,
+            usage,
+        };
         let mut ptr : *mut u8 = std::ptr::null_mut();
 
-        let buffer = Buffer {
+        let id = wgn::wgpu_device_create_buffer_mapped(self.id, &desc, &mut ptr as *mut *mut u8);
-            id: wgn::wgpu_device_create_buffer_mapped(self.id, desc, &mut ptr as *mut *mut u8),
-        };
 
-        let data = unsafe { std::slice::from_raw_parts_mut(ptr as *mut T, desc.size as usize / std::mem::size_of::<T>()) };
+        let data = unsafe { std::slice::from_raw_parts_mut(ptr as *mut T, count) };
 
-        (buffer, data)
+        CreateBufferMapped{id, data}
     }
 
     pub fn create_texture(&self, desc: &TextureDescriptor) -> Texture {