replacer shaders

Compute shaders for remapping Vulkan resources during capture/replay, used by GFXReconstruct. This repo exists to give the shaders their own home and make them easier to iterate on outside of the larger project.

What they do

Three compute shaders, each dispatched at replay time to fix up resource handles that differ between the original capture and the replay environment:

replacer_bda — remaps buffer device addresses. Walks an array of pointers, looks each captured address up in a sorted range map via binary search, and writes the corresponding replay-time address. A hashmap blacklist prevents double-replacement if the same location gets visited more than once.

replacer_sbt — remaps shader group handles inside a shader binding table. Captures store opaque 32-byte handles that are driver-specific; this shader translates them to the replay driver's equivalent using a hashmap lookup.

replacer_rehash — utility shader that migrates all entries from one hashmap into a larger one. Used when the blacklist or handle map needs to grow between dispatches.

Two flavours

The shaders exist in two forms:

• GLSL (.comp files) — what GFXReconstruct currently uses in production. Targets #version 460 with GL_EXT_buffer_reference2, GL_EXT_scalar_block_layout, GL_EXT_shader_explicit_arithmetic_types_int64, and GL_EXT_shader_atomic_int64.

• Slang (.slang files) — a port of the same logic using Slang. Cleaner generics, interface-based hashmap (hashmap_t<K, V> / mutable_hashmap_t<K, V>), and proper module separation. Not yet wired into GFXReconstruct.

Hashmap

Both flavours use the same open-addressing linear-probe hashmap with lock-free atomic insertion (atomicCompSwap / InterlockedCompareExchange). Keys and values are either uint64_t device addresses or 32-byte shader_group_handle_t structs. Hashing is xxHash32 (scalar variant from Jarzynski & Olano 2020).