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Unreal Engine X - Backports and Engine Fixes

This page collects the currently identified backports and related engine fixes.

The inventory distinguishes existing branch changes from newer local integrations. An entry does not imply that the complete UE6 subsystem has been imported.

Applied Backports​

These entries describe applied source changes. Runtime validation and performance verification remain ongoing where applicable.

CPU and Multithreading​

  • CPU01 - DX12 descriptor arrays - Reduces allocations and pointer chasing.
  • CPU02 - Batched PSO deletion - Spreads pipeline cleanup across calls, disabled by default.
  • CPU03 - Chaos growth and bulk reserve - Reduces reallocations during particle transfers and spawning.
  • CPU04 - Batched Chaos view rebuilding - Avoids rebuilding particle views after every deletion.
  • CPU05 - Single-consumer pose-cache bypass - Skips unnecessary animation pose caching and copies.
  • CPU06 - Work-stealing contention yields - Limits repeated queue retries under contention.
  • CPU08 - Chaos graph-color batching - Reduces solver barriers through optional batching.
  • CPU11 - Binned allocator cache-line separation - Separates pool locks from frequently accessed data.
  • CPU12 - I/O completion lock batching - Groups request bookkeeping under one lock.
  • CPU13 - Current-platform CVar shortcut - Avoids unnecessary shader-platform name conversion.
  • CPU20 - Skeletal update data release - Frees abandoned or superseded dynamic-data blocks.

Nanite and Foliage​

  • NAN01 - Nanite RT reference-error reset - Resets reference state on empty or disabled paths.
  • NAN03 - CLAS assembly hit transforms - Shades assembly hits with the matching ID-decoder compatibility fix.
  • NAN05 - PrimeHZB PSO precaching - Adds the optional primary depth-only raster variant.
  • NAN08 - Deterministic Nanite sorting - Adds tie-breakers and updates the derived-data key.
  • NAN09 - Nanite custom-UV evaluation - Evaluates required vertex interpolants without WPO.
  • NAN12 - Final-level Nanite tessellation - Prevents another subdivision after the last supported split level.
  • NAN13 - Optional voxel traversal variant - Adds Epic's opt-in traversal variant, disabled by default.

Virtual Shadow Maps​

  • VSM01 - Async-compute shadow projection - Allows projection queue overlap, disabled by default.
  • VSM05 - Quad page-hole propagation - Shares coarser-page searches across 2x2 pages.
  • VSM07 - Shared WPO invalidation state - Keeps Nanite and non-Nanite shadow-cache decisions consistent.

Correctness​

  • FIX01 - DX12 PSO atomic publication - Uses acquire/release ordering for initialized states.
  • FIX02 - DOF group-barrier fix - Moves synchronization outside a first-lane branch.
  • FIX03 - I/O strong compare-exchange - Prevents spurious one-shot cancellation and error failures.
  • FIX04 - Lumen rough-metal albedo boost - Boosts combined diffuse and rough-specular bounce albedo.
  • FIX05 - Vulkan float16 volume readback - Corrects element counts and zero-fill byte sizes.
  • FIX07 - Skylight irradiance refresh - Clears stale lighting when sky data disappears.

GPU Rendering​

  • GPU01 - Nanite material-export compaction - Redistributes VRS exports for better GPU stores.

Vulkan / Future Linux​

  • VK01 - Vulkan sampler descriptor stride - Uses the correct descriptor-heap sampler stride.
  • VK02 - Vulkan transient callback captures - Avoids large copies in synchronous creation callbacks.
  • VK05 - Texel-buffer draw workaround - Adds an optional GPU-hang serialization workaround, disabled by default.

UnrealBuildTool​

  • Plugin module exclusion - Adds per-target DisablePluginModules configuration to omit selected modules from an enabled plugin's automatic build list. Dependency resolution and runtime loading still require separate consideration.