This is required to properly optimize signatures, because these
semantics must be alligned while being packed:
- Array elements.
- The first fields of structs.
- Major vectors of a matrix.
For now this has no effect since semantics are allocated with reg_size
4, but will have effect when optimizing interstage signatures.
The generated pixel shader input signature must be consistent with the
generated vertex shader output signature for the same data type.
Since the interpolation mode affects allocation order, the allocator
needs to know the modifiers for both input and output signature elements.
The descriptor heap implementation is a rather central behavior element
in vkd3d, so it's useful to have all the relevant information logged
in a single place.
The goal is to make a requirement for VSIR that signature element
masks are always contiguous. The SPIR-V backend already implicitly
makes that assumption, since it just consider the LSB and popcount
of the mask.
For example, consider this HLSL pixel shader:
float4 main(float4 color : COLOR) : SV_Target
{
return float4(color.x, 10.0f, 11.0f, color.w);
}
Currently the parser describes the input signature element
corresponding to semantic COLOR as having mask .xw, which is
sensible. However, the SPIR-V parser will interpret that as
a mask starting at x and with popcount 2, and assuming it is
contiguous it will implicitly act as if it were .xy. This is
not correct, because the wrong component will be loaded from
the vertex stage.
Slightly simplifies descriptor write addressing, and makes layouts
essentially the same as array layouts, differing only in the binding
details, and therefore easier to understand. This also simplifies the
addition of storage buffer bindings, which can all be added onto the end.
Allows descriptor set layouts to be created after all bindings are
mapped. This is less complex and fragile than the current scheme, and in
a future patch it will support separating descriptor types into different
sets. Descriptors on virtual heaps are currently allocated from pools
which contain an equal number of each descriptor type used by vkd3d, and
this can waste a significant amount of device memory.
