Struct bevy::render::render_resource::Buffer

pub struct Buffer { /* private fields */ }

Implementations

impl Buffer

pub fn id(&self) -> BufferId

pub fn slice(&self, bounds: impl RangeBounds<u64>) -> BufferSlice<'_>

Examples found in repository

examples/shader/shader_instancing.rs (line 259)

    fn render<'w>(
        item: &P,
        _view: (),
        instance_buffer: Option<&'w InstanceBuffer>,
        (meshes, render_mesh_instances): SystemParamItem<'w, '_, Self::Param>,
        pass: &mut TrackedRenderPass<'w>,
    ) -> RenderCommandResult {
        let Some(mesh_instance) = render_mesh_instances.render_mesh_queue_data(item.entity())
        else {
            return RenderCommandResult::Failure;
        };
        let Some(gpu_mesh) = meshes.into_inner().get(mesh_instance.mesh_asset_id) else {
            return RenderCommandResult::Failure;
        };
        let Some(instance_buffer) = instance_buffer else {
            return RenderCommandResult::Failure;
        };

        pass.set_vertex_buffer(0, gpu_mesh.vertex_buffer.slice(..));
        pass.set_vertex_buffer(1, instance_buffer.buffer.slice(..));

        match &gpu_mesh.buffer_info {
            GpuBufferInfo::Indexed {
                buffer,
                index_format,
                count,
            } => {
                pass.set_index_buffer(buffer.slice(..), 0, *index_format);
                pass.draw_indexed(0..*count, 0, 0..instance_buffer.length as u32);
            }
            GpuBufferInfo::NonIndexed => {
                pass.draw(0..gpu_mesh.vertex_count, 0..instance_buffer.length as u32);
            }
        }
        RenderCommandResult::Success
    }

examples/shader/gpu_readback.rs (line 192)

fn map_and_read_buffer(
    render_device: Res<RenderDevice>,
    buffers: Res<Buffers>,
    sender: Res<RenderWorldSender>,
) {
    // Finally time to get our data back from the gpu.
    // First we get a buffer slice which represents a chunk of the buffer (which we
    // can't access yet).
    // We want the whole thing so use unbounded range.
    let buffer_slice = buffers.cpu_buffer.slice(..);

    // Now things get complicated. WebGPU, for safety reasons, only allows either the GPU
    // or CPU to access a buffer's contents at a time. We need to "map" the buffer which means
    // flipping ownership of the buffer over to the CPU and making access legal. We do this
    // with `BufferSlice::map_async`.
    //
    // The problem is that map_async is not an async function so we can't await it. What
    // we need to do instead is pass in a closure that will be executed when the slice is
    // either mapped or the mapping has failed.
    //
    // The problem with this is that we don't have a reliable way to wait in the main
    // code for the buffer to be mapped and even worse, calling get_mapped_range or
    // get_mapped_range_mut prematurely will cause a panic, not return an error.
    //
    // Using channels solves this as awaiting the receiving of a message from
    // the passed closure will force the outside code to wait. It also doesn't hurt
    // if the closure finishes before the outside code catches up as the message is
    // buffered and receiving will just pick that up.
    //
    // It may also be worth noting that although on native, the usage of asynchronous
    // channels is wholly unnecessary, for the sake of portability to WASM
    // we'll use async channels that work on both native and WASM.

    let (s, r) = crossbeam_channel::unbounded::<()>();

    // Maps the buffer so it can be read on the cpu
    buffer_slice.map_async(MapMode::Read, move |r| match r {
        // This will execute once the gpu is ready, so after the call to poll()
        Ok(_) => s.send(()).expect("Failed to send map update"),
        Err(err) => panic!("Failed to map buffer {err}"),
    });

    // In order for the mapping to be completed, one of three things must happen.
    // One of those can be calling `Device::poll`. This isn't necessary on the web as devices
    // are polled automatically but natively, we need to make sure this happens manually.
    // `Maintain::Wait` will cause the thread to wait on native but not on WebGpu.

    // This blocks until the gpu is done executing everything
    render_device.poll(Maintain::wait()).panic_on_timeout();

    // This blocks until the buffer is mapped
    r.recv().expect("Failed to receive the map_async message");

    {
        let buffer_view = buffer_slice.get_mapped_range();
        let data = buffer_view
            .chunks(std::mem::size_of::<u32>())
            .map(|chunk| u32::from_ne_bytes(chunk.try_into().expect("should be a u32")))
            .collect::<Vec<u32>>();
        sender
            .send(data)
            .expect("Failed to send data to main world");
    }

    // We need to make sure all `BufferView`'s are dropped before we do what we're about
    // to do.
    // Unmap so that we can copy to the staging buffer in the next iteration.
    buffers.cpu_buffer.unmap();
}

pub fn unmap(&self)

Examples found in repository

examples/shader/gpu_readback.rs (line 250)

fn map_and_read_buffer(
    render_device: Res<RenderDevice>,
    buffers: Res<Buffers>,
    sender: Res<RenderWorldSender>,
) {
    // Finally time to get our data back from the gpu.
    // First we get a buffer slice which represents a chunk of the buffer (which we
    // can't access yet).
    // We want the whole thing so use unbounded range.
    let buffer_slice = buffers.cpu_buffer.slice(..);

    // Now things get complicated. WebGPU, for safety reasons, only allows either the GPU
    // or CPU to access a buffer's contents at a time. We need to "map" the buffer which means
    // flipping ownership of the buffer over to the CPU and making access legal. We do this
    // with `BufferSlice::map_async`.
    //
    // The problem is that map_async is not an async function so we can't await it. What
    // we need to do instead is pass in a closure that will be executed when the slice is
    // either mapped or the mapping has failed.
    //
    // The problem with this is that we don't have a reliable way to wait in the main
    // code for the buffer to be mapped and even worse, calling get_mapped_range or
    // get_mapped_range_mut prematurely will cause a panic, not return an error.
    //
    // Using channels solves this as awaiting the receiving of a message from
    // the passed closure will force the outside code to wait. It also doesn't hurt
    // if the closure finishes before the outside code catches up as the message is
    // buffered and receiving will just pick that up.
    //
    // It may also be worth noting that although on native, the usage of asynchronous
    // channels is wholly unnecessary, for the sake of portability to WASM
    // we'll use async channels that work on both native and WASM.

    let (s, r) = crossbeam_channel::unbounded::<()>();

    // Maps the buffer so it can be read on the cpu
    buffer_slice.map_async(MapMode::Read, move |r| match r {
        // This will execute once the gpu is ready, so after the call to poll()
        Ok(_) => s.send(()).expect("Failed to send map update"),
        Err(err) => panic!("Failed to map buffer {err}"),
    });

    // In order for the mapping to be completed, one of three things must happen.
    // One of those can be calling `Device::poll`. This isn't necessary on the web as devices
    // are polled automatically but natively, we need to make sure this happens manually.
    // `Maintain::Wait` will cause the thread to wait on native but not on WebGpu.

    // This blocks until the gpu is done executing everything
    render_device.poll(Maintain::wait()).panic_on_timeout();

    // This blocks until the buffer is mapped
    r.recv().expect("Failed to receive the map_async message");

    {
        let buffer_view = buffer_slice.get_mapped_range();
        let data = buffer_view
            .chunks(std::mem::size_of::<u32>())
            .map(|chunk| u32::from_ne_bytes(chunk.try_into().expect("should be a u32")))
            .collect::<Vec<u32>>();
        sender
            .send(data)
            .expect("Failed to send data to main world");
    }

    // We need to make sure all `BufferView`'s are dropped before we do what we're about
    // to do.
    // Unmap so that we can copy to the staging buffer in the next iteration.
    buffers.cpu_buffer.unmap();
}

Methods from Deref<Target = Buffer>

pub fn as_entire_binding(&self) -> BindingResource<'_>

Return the binding view of the entire buffer.

Examples found in repository

examples/shader/gpu_readback.rs (line 148)

fn prepare_bind_group(
    mut commands: Commands,
    pipeline: Res<ComputePipeline>,
    render_device: Res<RenderDevice>,
    buffers: Res<Buffers>,
) {
    let bind_group = render_device.create_bind_group(
        None,
        &pipeline.layout,
        &BindGroupEntries::single(buffers.gpu_buffer.as_entire_binding()),
    );
    commands.insert_resource(GpuBufferBindGroup(bind_group));
}

pub fn as_entire_buffer_binding(&self) -> BufferBinding<'_>

Return the binding view of the entire buffer.

pub fn slice<S>(&self, bounds: S) -> BufferSlice<'_>

where S: RangeBounds<u64>,

Use only a portion of this Buffer for a given operation. Choosing a range with no end will use the rest of the buffer. Using a totally unbounded range will use the entire buffer.

pub fn unmap(&self)

Flushes any pending write operations and unmaps the buffer from host memory.

pub fn destroy(&self)

Destroy the associated native resources as soon as possible.

pub fn size(&self) -> u64

Returns the length of the buffer allocation in bytes.

This is always equal to the size that was specified when creating the buffer.

pub fn usage(&self) -> BufferUsages

Returns the allowed usages for this Buffer.

This is always equal to the usage that was specified when creating the buffer.

pub fn global_id(&self) -> Id<Buffer>

Returns a globally-unique identifier for this Buffer.

Calling this method multiple times on the same object will always return the same value. The returned value is guaranteed to be different for all resources created from the same Instance.

Trait Implementations

impl Clone for Buffer

fn clone(&self) -> Buffer

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Buffer

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Deref for Buffer

type Target = Buffer

The resulting type after dereferencing.

fn deref(&self) -> &<Buffer as Deref>::Target

Dereferences the value.

impl From<Buffer> for Buffer

fn from(value: Buffer) -> Buffer

Converts to this type from the input type.

impl From<Buffer> for SlotValue

fn from(value: Buffer) -> SlotValue

Converts to this type from the input type.