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kuba
82c2c7f48c
Ports the still-applicable half of the archived fork's stale-texture fix
(a42ccae) onto current main. Silent Hill: The Short Message (PPSA10112)
shows both faces: black title-screen UI (glyph atlas frozen at its first
upload) and stale/garbage rows on the brightness screen (a 3840x2160 UI
sheet whose backing bytes were never re-read).
1. Write tracking is armed under a byte budget, not a resolution cap.
GetOrCreateGuestImage armed GuestImageWriteTracker only when
target.Width <= 1920 && target.Height <= 1080. Silent Hill renders at
3840x2160, so every one of its render targets was excluded from
CPU-write tracking and no guest rewrite of one could ever invalidate
it: SyncCpuWrittenGuestImages (the flip / ACQUIRE_MEM re-upload path)
only ever visits ranges the tracker armed.
The cap presumably existed as a perf guard, but resolution is the
wrong proxy for the cost. Arming is one mprotect over the range, and
the fault handler unprotects the whole range on the first store, so a
write burst costs one fault regardless of size. What actually scales
with the surface is the dirty re-upload: one byte[byteCount]
allocation plus a full guest-memory read per dirty flip. So the guard
is now a byte budget, set equal to the 128 MiB limit that
SyncCpuWrittenGuestImages itself enforces before re-uploading. Above
that, arming can only cost faults; it can never produce a re-upload.
That is generous for 4K (RGBA8 32 MiB, RGBA16F 63 MiB, RGBA32F
127 MiB all fit) while still excluding volume textures that a
resolution cap could not see at all (512^3 RGBA8 is 512 MiB behind a
"512x512" surface).
Both sites now also arm the exact extent recorded in
_guestImageExtents (GetTextureByteCount) instead of
Width*Height*depth*GetTextureBytesPerPixel, so the armed range and
the range the sync path reads back are the same bytes; the old
expression over-counted block-compressed and unknown formats.
2. The CPU-texture refresh path no longer gates on IsCpuBacked alone.
TryCreateCpuTextureRefreshResource bailed on !guestImage.IsCpuBacked.
That flag is a latch: it flips false the first time an address is
used as a render target and never flips back. A surface that was
rendered into once and is afterwards rewritten by the guest CPU was
therefore frozen at its last GPU content forever, even when the parse
thread had already shipped fresh texels for it.
The gate is replaced by ShouldRefreshGuestImageFromCpu: CPU-backed,
or the parse-time write generation is above zero and differs from the
generation recorded by the last upload. Keeping the positive-
generation requirement preserves the pure GPU-feedback case (render
into an image, then sample it) that IsCpuBacked used to protect: such
a surface is now tracked (change 1) but never CPU-written, so its
generation stays zero and its live image is left alone. This matters
more than it did in the fork, precisely because change 1 arms
tracking on far more render targets. Dropping the gate outright, as
the fork did, would let a target sampled under a format tag that the
availability map does not match be overwritten once with whatever
sits in guest memory.
The existing content fingerprint still suppresses redundant uploads,
and MarkSampledImagesInitialized records the uploaded generation, so
a rewritten surface re-uploads exactly once per guest write burst.
Not ported: the fork's third part added a PeekDirty guard to the
parse-time snapshot fast path in AgcExports. It is superseded. That path
now calls IsGuestImageUploadKnown, which already compares
_cpuBackedUploadGenerations against the tracker's write generation - a
monotonic value that survives another owner consuming the dirty flag,
unlike PeekDirty, which both EvictDirtyCachedTextures and
SyncCpuWrittenGuestImages clear. Guest images with no generation entry
are covered instead by SyncCpuWrittenGuestImages. Adding a non-consuming
PeekDirty there would also make every draw between a CPU write and the
next flip fall through to a full texel re-read of the surface (33 MiB
for a 4K sheet), since Track re-arms without clearing the dirty flag.
The fork's promotion-path Track ("vulkan.cpu-backed-image") is likewise
superseded: AgcExports already arms every sampled texture's backing
extent as "agc.decoded-texture" before reading its texels.
Both decisions are extracted as pure internal predicates so they can be
unit-tested; the Vulkan device code around them needs a real device.