(buffer …)

Creates a GPU buffer for storing vertex data, uniforms, storage data, or indices.

Syntax

(buffer :name name
  :size 1024
  :usage [vertex storage]
  :pool 2)

A buffer whose initial contents come from a (data …) entry writes :data instead of :size: the data sizes it.

Keys

Key	Type	Required	Default	Description
:name	symbol	Yes	-	Unique buffer name
:usage	array	Yes	-	Usage flags, at least one
:size	number/expression/(define …) name	No*	-	Size in bytes
:data	reference	No*	-	A (data …) entry whose bytes fill the buffer at creation, and size it
:index-of	reference	No*	-	Size + bytes + index-format from an indexed shape
:file	string	No*	-	WASM file whose exports supply size + initial bytes
:index-format	symbol	No	-	uint16 / uint32 when bound as an index buffer without :index-of
:pool	number	No	1	Ping-pong buffer pool size (1 to 255)

*A buffer has to name its size somehow: :size, or one of :data, :index-of and :file, which size it from the bytes they carry. Naming none of the four is a compile error that points at the form.

:size

Type: number | expression | (define …) name

Buffer size in bytes: a non-negative integer. Can be:

• Number: :size 1024
• Expression: :size (* 4 256) (evaluated at compile time)
• (define …) name: :size VERTEX_BYTES, on its own or inside an expression

A (data …) name is not one of them. Bytes and the size they imply are said once, with :data.

(define :name VERTEX_SIZE :value 40)
(define :name VERTEX_COUNT :value 100)
(define :name VERTEX_BYTES :value 4000)

(buffer :name vertices
  :size (* VERTEX_SIZE VERTEX_COUNT)
  :usage [vertex])

(buffer :name morePositions
  :size VERTEX_BYTES
  :usage [vertex])

A uniform buffer of fewer than 16 bytes is refused: that is WebGPU’s floor for a uniform binding.

:usage

Type: array of symbols

GPU buffer usage flags. At least one required.

Flag	Description
vertex	Vertex buffer
index	Index buffer
uniform	Uniform buffer (var<uniform>)
storage	Storage buffer (var<storage>)
copy-src	Source of copy operations
copy-dst	Destination of copies and write-buffer ops
indirect	Holds indirect draw/dispatch arguments
query-resolve	Receives resolve-query-set results
map-read	Mappable for CPU readback; combines with copy-dst and nothing else
map-write	Mappable for CPU upload; combines with copy-src and nothing else

A mappable buffer is host memory the GPU may only copy in or out of, so the two map flags do not combine with vertex, storage, uniform and the rest. The compiler reports the combination rather than leaving it to the device.

(buffer :name storageBuffer
  :size 4096
  :usage [storage copy-dst])

:data

Type: reference

Reference to a (data …) form holding the buffer’s initial contents. The buffer is created with those bytes already mapped, and takes its size from them, so :size is not written beside it. copy-dst is added to the usage flags automatically.

(data :name cubeVertices (cube :format [position4 color4 uv2]))

(buffer :name vertexBuffer
  :usage [vertex]
  :data cubeVertices)

Writing a numeric :size beside :data is legal and means what it says: the buffer is that many bytes and the data fills the front of it. A :size smaller than the data is a compile error.

:index-of

Type: reference

Sources the buffer’s size, initial bytes, and index-format from an indexed shape’s index data (teapot, dragon). This references the shape (data …) directly; no synthetic _indices name is needed.

(data :name teapotMesh (teapot :format [position3 normal3]))

(buffer :name indexBuffer :index-of teapotMesh :usage [index])

:index-format

Type: symbol (uint16 | uint32)

The byte width of index entries. With :index-of, the format propagates from the shape’s index data and this key is unnecessary. Set it explicitly when a buffer is bound as a pass’s :index-buffer without an :index-of source, for example when a compute pass generates the indices:

(buffer :name genIndices :size 4096 :usage [index storage] :index-format uint32)

:file

Type: string (file path relative to the source)

A WASM (WebAssembly) module whose l / s / gen exports supply both the buffer’s size and its initial bytes, so :size is not authored at all. This is the same module convention the (pass … :data …) sugar uses, and the sugar synthesizes such buffers for you.

(buffer :name palette :usage [storage] :file "colors.wasm")

:pool

Type: number (1 to 255)

Creates multiple buffer instances for ping-pong patterns (alternating each frame between the instance being read and the instance being written). Used in compute simulations where you read from one buffer and write to another.

(buffer :name particles
  :size 32768
  :usage [vertex storage]
  :pool 2)

With :pool 2, the runtime creates two buffer instances. Selection uses:

actual_id = base_id + (frame_counter + pool_offset) % pool_size

See Ping-Pong Pattern below.

Examples

Simple Vertex Buffer

(buffer :name positions :size 48 :usage [vertex])

Uniform Buffer with Copy

(buffer :name uniforms :size 16 :usage [uniform copy-dst])

Shape Generator Buffer

Use compile-time shape generators for mesh data:

(data :name cubeVertices (cube :format [position4 color4 uv2]))

(buffer :name vertexBuffer
  :usage [vertex]
  :data cubeVertices)

:data sizes the buffer from the generated shape data, so there is no byte count to write down or keep in step.

Indexed Mesh Buffers

An indexed shape produces both vertex data and an index companion. Size the vertex buffer from the shape and the index buffer with :index-of:

(data :name teapotMesh (teapot :format [position3 normal3]))

(buffer :name vertexBuffer
  :usage [vertex]
  :data teapotMesh)

(buffer :name indexBuffer :index-of teapotMesh :usage [index])

Manual Data Buffer

(data :name triangleVerts :float32 [
    0.0  0.5  1 0 0
   -0.5 -0.5  0 1 0
    0.5 -0.5  0 0 1
])

(buffer :name vertexBuffer
  :usage [vertex]
  :data triangleVerts)

Compute Storage Buffer

(define :name NUM_PARTICLES :value 2048)
(define :name PARTICLE_SIZE :value 16)

(buffer :name particles
  :size (* NUM_PARTICLES PARTICLE_SIZE)
  :usage [vertex storage]
  :pool 2)

Ping-Pong Pattern

For compute simulations requiring double-buffering:

(buffer :name particles
  :size 32768
  :usage [vertex storage]
  :pool 2)

(bind-group :name simBindGroup :layout simPipeline :group 0 :pool 2
  (entry :binding 0 :buffer particles :ping-pong 0)
  (entry :binding 1 :buffer particles :ping-pong 1))

(compute-pass :name simulate
  :pipeline simPipeline
  :bind-groups [simBindGroup]
  :bind-groups-pool-offsets [0]
  (dispatch :workgroups [32]))

Each frame alternates which buffer is read vs written.

Validation Rules

Rule	Error
A name is declared once, across every form kind	duplicate_cross_ref_target, or duplicate name 'x': already declared as a (buffer …) at line N
A builtin spelling (canvas, context-current-texture, the runtime input sources) cannot be declared	'canvas' is a builtin symbol and cannot name a (buffer …)
:usage required	missing_required_key
:usage needs at least one flag	vector_too_short
:data / :index-of must reference a (data …)	not_cross_ref
:size must be a non-negative integer, or a declared (define …) name	number_below_min, not_cross_ref
:pool must be in [1,255]	number_below_min / number_above_max
The buffer has to name its size	buffer 'b' names no size: give it :size …, or :data …, or :index-of …, or :file …
:size may not be smaller than :data	buffer 'b' size (N bytes) is smaller than data 'd' (M bytes)
A uniform buffer is at least 16 bytes	uniform buffer 'b' size (N bytes) is below WebGPU's 16-byte uniform floor
map-read combines only with copy-dst, map-write only with copy-src	buffer 'b' is :usage [map-read … storage …]
A copy endpoint carries the usage the copy needs	buffer 'b' is the :source of a copy but its :usage has no copy-src

The rows with a code are schema checks; the rows with a message are compiler checks that read a value rather than a shape, and they report the line the form is written on.

WebGPU Mapping

Maps to GPUBuffer:

device.createBuffer({
  size: size,
  usage: GPUBufferUsage.VERTEX | GPUBufferUsage.STORAGE,
  mappedAtCreation: hasMappedData
});

Related

• (data …) - Define buffer data and shape generators
• (bind-group …) - Bind buffers to shaders
• (render-pass …) - Use as vertex buffer
• (queue …) - Write data to buffer at runtime