Chromium Experimental Dynamic Binding

The chromium_experimental_dynamic_binding is an experimental extension that provides different prototype options to support the WebGPU bindless prototypes.

There are currently two different prototypes included in this extension:

A resource_binding type.
A Resource Table which is accessible through getResourceandhasResource`

Status

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

Availability

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

`resource_binding`

A new resource_binding type is added
A resource_binding cannot 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, resource_binding, write>).
A resource_binding can not be accessed with the usual array subscript operators. e.g. the following is disallowed:
```
var a: resource_binding;
fn foo() {
    var b = a[0];
}
```
Two helper methods getBinding and hasBinding are provided for accessing a resource_binding.

`hasBinding`

@must_use fn hasBinding<T>(a: resource_binding, 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: resource_binding, 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: resource_binding) -> u32

Returns the length of the array.

Resource table

The concept of a Resource Table is added to WGSL. This is not a type which can be written, or an address space, but a data table available to use with the getResource and hasResource methods. The table is made available by the system and is just accessible.

`hasResource`

@must_use fn hasResource<T>(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.

hasResource returns true if the item a index of the resource table is of type T.

`getResource`

@must_use fn getResource<T>(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.

getResource returns the value in the resource table at index of type T.

If index is outside the bounds of the resource table then a default value of type T will be returned. If the item at index is not of type T then a default value of type T is returned. Essentially, a value is always returned, it may just be a synthensized default value.

Example usage

`resource_binding`

enable chromium_experimental_dynamic_binding;

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

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

Resource Table

enable chromium_experimental_dynamic_binding;

const kHouseTexture = 0u;

@fragment fn fs() {
    if (hasResource<texture_2d<f32>>(kHouseTexture)) {
        let tex = textureLoad(getResource<texture_2d<f32>>(kHouseTexture));
    }
}