Add empty constructors to structs with resource fields

[jvepsalainen-nv]

Description

Problem

RTX Remix shaders fail to compile with recent versions of the Slang shader compiler (v2025.23.2+) due to error 41024:

error 41024: cannot default-initialize struct 'DirectPathTextures' with '{}' 
because it contains an uninitialized texture field

This error occurs when attempting to instantiate structs that contain resource types (e.g., Texture2D, RWTexture2D) without providing explicit initialization for those fields.

Root Cause

Slang recently introduced stricter validation to prevent default-initialization of resource types using empty braces {}. This is because downstream compilers like DXC do not support default-initializing resources, making this pattern unsafe and non-portable.

The error triggers when code like this is encountered:

struct DirectPathTextures {
  RWTexture2D<uint16_t> SharedFlags;
  // ... more resource fields
};

// This line triggers error 41024 in Slang 2025.23+:
DirectPathTextures directPathTextures;

Solution

Add empty constructors __init() {} to structs containing resource fields that are explicitly instantiated in shader code:

File: src/dxvk/shaders/rtx/algorithm/path_state.slangh

struct DirectPathTextures
{
  __init() {}  // Empty constructor prevents error 41024

  RWTexture2D<uint16_t> SharedFlags;
  RWTexture2D<uint16_t> SharedMediumMaterialIndex;
  // ... other fields
};

struct IndirectPathTextures
{
  __init() {}  // Empty constructor prevents error 41024

  Texture2D<float4> PrimaryWorldPositionWorldTriangleNormal;
  RWTexture2D<float4> IndirectRadianceHitDistance;
};

The empty constructor allows the struct to be instantiated without attempting to default-initialize the resource fields. The existing code pattern of field-by-field assignment continues to work correctly:

DirectPathTextures directPathTextures;  // OK with __init() {}
directPathTextures.SharedFlags = SharedFlags;
directPathTextures.SharedMediumMaterialIndex = SharedMediumMaterialIndex;
// ... assign other fields

Why Only These Structs?

Fixed (2 structs):

• DirectPathTextures - explicitly instantiated in integrate_direct.slangh
• IndirectPathTextures - explicitly instantiated in integrate_indirect.slangh, integrate_indirect_closesthit.rchit.slang, and integrate_indirect_miss.rmiss.slang
• This is a minimal, non-breaking change required for compatibility with current and future Slang compiler versions. It does not affect shader functionality or performance.

Not Fixed (6+ structs):

• AliasedData0, AliasedData1, AliasedData2 (in various *_bindings.slangh files)

These are declared as uniform struct bindings:

layout(binding = X)
uniform struct AliasedData0 {
  Texture2D<float4> SomeField;
  RWTexture2D<float4> AnotherField;
} aliasedData0;  // This is a shader input binding, NOT a construction

The uniform struct pattern declares a shader input binding (similar to a uniform buffer), not a struct instance. These are never instantiated or constructed in shader code - they're bound by the host application. Therefore, they don't trigger error 41024 and don't need the fix.

Related

• Remix issue Add empty constructors to resource-containing structs for Slang 2025.23+ compatibility #118
• Slang issue Additional codebase for CI testing shader-slang/slang#8655
• Slang diagnostic: error 41024 (cannotDefaultInitializeResource)
  • Link to slang-diagnostic-defs.h
• This fix enables the RTX Remix nightly CI to pass with the latest Slang and Remix

[jvepsalainen-nv]

Tested in Slang Remix shader compile CI with PR shader-slang/slang#9188.
Test log: https://github.com/shader-slang/slang/actions/runs/19926280263/job/57126769583