Struct naga::back::spv::GlobalVariable

struct GlobalVariable {
    var_id: Word,
    handle_id: Word,
    access_id: Word,
}

The SPIR-V representation of a crate::GlobalVariable.

In the Vulkan spec 1.3.296, the section Descriptor Set Interface says:

Variables identified with the Uniform storage class are used to access transparent buffer backed resources. Such variables must be:

• typed as OpTypeStruct, or an array of this type,

• identified with a Block or BufferBlock decoration, and

• laid out explicitly using the Offset, ArrayStride, and MatrixStride decorations as specified in “Offset and Stride Assignment”.

This is followed by identical language for the StorageBuffer, except that a BufferBlock decoration is not allowed.

When we encounter a global variable in the Storage or Uniform address spaces whose type is not already Struct, this backend implicitly wraps the global variable in a struct: we generate a SPIR-V global variable holding an OpTypeStruct with a single member, whose type is what the Naga global’s type would suggest, decorated as required above.

The helpers::global_needs_wrapper function determines whether a given crate::GlobalVariable needs to be wrapped.

Fields

var_id: Word

The SPIR-V id of the OpVariable that declares the global.

If this global has been implicitly wrapped in an OpTypeStruct, this id refers to the wrapper, not the original Naga value it contains. If you need the Naga value, use access_id instead of this field.

If this global is not implicitly wrapped, this is the same as access_id.

This is used to compute the access_id pointer in function prologues, and used for ArrayLength expressions, which need to pass the wrapper struct.

handle_id: Word

The loaded value of a AddressSpace::Handle global variable.

If the current function uses this global variable, this is the id of an OpLoad instruction in the function’s prologue that loads its value. (This value is assigned as we write the prologue code of each function.) It is then used for all operations on the global, such as OpImageSample.

access_id: Word

The SPIR-V id of a pointer to this variable’s Naga IR value.

If the current function uses this global variable, and it has been implicitly wrapped in an OpTypeStruct, this is the id of an OpAccessChain instruction in the function’s prologue that refers to the wrapped value inside the struct. (This value is assigned as we write the prologue code of each function.) If you need the wrapper struct itself, use var_id instead of this field.

If this global is not implicitly wrapped, this is the same as var_id.

Implementations

impl GlobalVariable

const fn dummy() -> Self

const fn new(id: Word) -> Self

fn reset_for_function(&mut self)

Prepare self for use within a single function.

Trait Implementations

impl Clone for GlobalVariable

fn clone(&self) -> GlobalVariable

Returns a copy of the value.

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

Performs copy-assignment from source.