Thrones of Britannia Engine Performance Fix

Source code for the Total War Saga: THRONES OF BRITANNIA engine performance mod: a dinput8.dll that the game loads at startup and that patches the engine in memory. No game files are changed. Thrones runs on Attila's engine, so this is a port of the Attila Engine Performance Fix: every fix whose code is the same in Thrones was carried over, with its test.

Download the ready-made DLL:

• Steam Workshop: https://steamcommunity.com/sharedfiles/filedetails/?id=3828420829 (after subscribing, run install.bat in the mod's folder)

Created with the help of AI (Claude by Anthropic). Tested in game by JGdaCaesar.

It also carries the game side of the separate DLSS add-on "Upscaling and Framegen for Thrones of Britannia" (NVIDIA DLSS Super Resolution and Frame Generation): it only starts when the add-on's FrameBridge folder is in the game folder, otherwise none of it runs. The add-on's 64-bit helper is its own repository: https://github.com/JSa25/TotalWarUpscalingFramegen

What each file does

File	Fix
proxy.c	Entry point (DllMain, or a DLL load notification when something loaded dinput8.dll before the game DLL), dinput8 forwarding, tobfix.log with the STATUS block, the off switches
heapfix.c	The main fix: replaces the game's single-lock dlmalloc heap with mimalloc for blocks up to 16 KB (its own 512-768 MB reservation, grown in 32 MB best-fit pieces); larger blocks stay on the game's dlmalloc
pool.c	Faster free lookup for the engine's small-object pools
sortfix.c	The two render-list sorts (by +0x6C/+0x68 and +0x4C/+0x48): key extraction plus radix sort, same order as the game's sorts
campfix.c	Campaign map: four x87 rounding-mode blocks (fog of war, terrain height, curve table)
x87fix.c	The same x87 rounding idiom at the ~1,260 other sites in the engine (fisttp / SSE4.1 roundss)
frame.c	Hook on the tile-feedback scan, which runs once per frame, for the rounding-mode safety checks of campfix.c and x87fix.c
memfast.c	Fast path for the engine's two memcpy/memmove copies on copies of 64 bytes or less
loopfetch.c	Three battle render loops prefetch the field the loop reads next, four items ahead (prefetch only, never a load through an item pointer)
fileio.c	Loading: .pack files opened without FILE_FLAG_NO_BUFFERING; small reads of read-only files in the game's user folder (the unpacked save) served from a 64 KB buffer, file position kept exactly
attrcache.c	Loading and menus: cache of missing loose-file folders behind the game's GetFileAttributesW and read-only CreateFileW calls. Every folder above a cached name is watched; any change clears the cache. Answers and last-error values are the same as Windows'
texfix.c	Battle loading: the DXT1 compressor for unit imposters redone with SSE2, byte-identical output
uikeep.c	Menus: the deletion step of the UI picture queue keeps a picture loaded instead of deleting it and remembers its name, up to 1,024
update.c	Self-update from the Steam Workshop copy (compares a version marker in the file; never downgrades, no network). Also updates the DLSS add-on: from the one Workshop item its install.bat recorded (FrameBridge\source.txt), only when that item's FrameBridge\version.txt is higher; settings.txt and logs are kept
bridgeprobe.c	DLSS add-on, game side (only with <game>\FrameBridge\helper64.exe): finds the frame without the HUD, the camera and the scene depth in the game's Direct3D 11 calls, moves the game's swapchain to a hidden window, jitters the viewport for DLSS, reads FrameBridge\settings.txt
fgbridge.c	Hands each frame (picture, depth, camera motion) to the 64-bit helper through shared textures and fences, and paces the game to it; stops the helper and falls back to the game's own frames if it stops answering
fgb_proto.h	The shared-memory layout and fences between fgbridge.c and the helper (the same file in the helper's repository)
fgpanel.c	The F11 settings panel drawn over the frame
r2motion.c, r2motionvs.h	Per-object motion vectors for moving soldiers and horses: the animated models drawn again on the GPU with the game's own skinning, matched to the previous frame by position
diag.c	Diagnostics in tobfix.log: mod version, game build and whether it is supported, system, settings, other hook DLLs, and crash records with a plain line saying whose code it was (a vectored exception handler that only logs)
logtrim.c	Keeps tobfix.log under about 1 MB
builds.h, version.h, dinput8.def	Known game builds, the mod version, the exports a dinput8.dll must have

Every patch first compares the game's bytes at its address with what it expects, and skips itself (and says so in tobfix.log) if they differ. So on another game version it does nothing.

Building

You need:

• llvm-mingw (the release used: 20261006, UCRT, x86_64 host), with its bin folder on PATH
• the mimalloc v3.5.3 source, in a folder named mimalloc next to build.bat (or set MIMALLOC to its path)

Then run:

build.bat

The DLL lands in build\dinput8.dll. The build is reproducible: with the same llvm-mingw and mimalloc versions you should get exactly the same file as the released one. Compare the SHA-256 (certutil -hashfile build\dinput8.dll SHA256) with dinput8.dll.sha256.

Automated builds

Every commit is also built on GitHub's own machines by .github/workflows/build.yml, with the compiler and mimalloc downloaded from their official releases (checksums pinned). Open the latest run under Actions: its summary shows the SHA-256 of the DLL, and the DLL itself can be downloaded there. Builds also carry a signed build attestation (gh attestation verify dinput8.dll -R JSa25/ThronesEnginePerfFix).

Tests

The tests run the game's own code next to the replacements on millions of inputs and check the results are identical. lateload_test loads the built DLL before the game DLL, as an overlay can, and checks every fix still installs from Windows' load notification; diag_test checks the crash records on deliberate faults; fileio_test and attrcache_test compare against plain Windows calls on a temporary folder tree while it changes; uikeep_test runs the menu fix against a stand-in for the game's picture table; selfupd_test checks the update rules (the DLL and the DLSS add-on) on throwaway files; bridgelive_test runs the DLSS add-on's game side against a stand-in game on your graphics card (addon: its settings) and r2motion_test the per-object motion vectors against values worked out on the CPU. They read your copy of the game's empire.retail.dll (it is not included here):

build.bat test "C:\...\steamapps\common\Total War Saga Thrones of Britannia\empire.retail.dll"

License

See LICENSE. mimalloc is (c) Microsoft Corporation and Daan Leijen, MIT license (third_party/mimalloc-LICENSE.txt).