Chromium Experimental Dynamic Binding

The chromium_experimental_dynamic_binding is an experimental extension that allows using both runtime sized binding_array and type-less binding_array. This provides the needed basis for dynamic binding (a.k.a. bind-less).

Status

This extension is experimental and the syntax is being discussed. No official WebGPU specification has been written yet.

Availability

| Platform | Notes | | SPIR-V | Requires SPV_EXT_descriptor_indexing extension and RuntimeDescriptorArray capability | | HLSL | Supported for DXC, not FXC | | MSL | Supported (TODO determine if there are Metal version restrictions) | | GLSL | Not supported |

Due to limited availability, this will need an enable statement to be used. For this experimental extension it would be enable chromium_experimental_dynamic_binding.

Specification

This extension adds new features to the binding_array feature added previously with the sized_binding_arrays extension [1].

binding_array<T>

  • A new binding_array<T> type is added.
  • T is a format-less storage texture (e.g. texture_storage_2d<f32>), sampled texture, multisampled texture, or depth texture.
  • This is a runtime-array version of the binding_array<T, N> as added by sized_binding_arrays.
  • A runtime binding array may not be passed as a function parameter. This is because there is no way in WGSL to currently write the needed pointer type (e.g. ptr<handle, binding_array<texture_1d<f32>>, write>).
  • An out-of-bounds read from the binding_array<T> will return any value from the binding_array.

arrayLength

@must_use fn arrayLength(a: ptr<handle, binding_array<T>, RW>) -> u32

Similar to the runtime-array version, returns the length of the array.

binding_array

  • A new binding_array type is added

  • This is a type-less version of binding_array<T>. As such, any restrictions on runtime binding array is relevant to binding_array.

  • A binding_array can not be accessed with the usual array subscript operators. e.g. the following is disallowed:

    var a: binding_array;
fn foo() {
    var b = a[0];
}

  • Two helper methods getBinding and hasBinding are provided for accessing a binding_array.

hasBinding

@must_use fn hasBinding<T>(a: binding_array, index: I) -> bool
  • I is an i32 or u32
  • T is a format-less storage texture (e.g. texture_storage_2d<f32>), sampled texture, multisampled texture, or depth texture.

hasBinding returns true if the item a index of the array is of type T.

getBinding

@must_use fn getBinding<T>(a: binding_array, index: I) -> T
  • I is an i32 or u32
  • T is a format-less storage texture (e.g. texture_storage_2d<f32>), sampled texture, multisampled texture, or depth texture.

getBinding returns the value at index of type T.

If index is outside the bounds of the binding array then a default texture of type T will be returned. If the item at index is not of type T then a default texture of type T is returned.

arrayLength

@must_use fn arrayLength(a: ptr<handle, binding_array, RW>) -> u32

Similar to the runtime-array version, returns the length of the array.

Example usage

binding_array<T>

enable chromium_experimental_dynamic_binding;

@group(0) @binding(0) var sampled_textures : binding_array<texture_2d<f32>>;

@fragment fn fs() {
    let texture_load = textureLoad(sampled_textures[0], vec2(0, 0), 0);
}

binding_array

enable chromium_experimental_dynamic_binding;

@group(0) @binding(0) var textures : binding_array;

@fragment fn fs() {
    if (hasBinding<texture_2d<f32>>(textures, 0)) {
        let tex = textureLoad(getBinding<texture_2d<f32>>(textures, 0));
    }
}

References

1.Sized Binding Arrays