Two changes, one measurement. The V6m smoke pair put GL versus Vulkan at
Holtburg at 18.52% of the frame differing at tolerance 2 with MSAA off. The same
stop on the same instrument now measures 9.05%, and the two populations these
address are gone from the difference map rather than merely smaller.
1. THE WORLD ATLASES WERE SAMPLED WITHOUT ANISOTROPY ON VULKAN, AND WITH THE
DEVICE MAXIMUM ON GL.
RhiWorldTextureArray -- the backend-neutral shared object/material atlas, and
the only IWorldTextureArray the Vulkan arm ever constructs -- registered its
clamp and repeat slots with GpuSamplerDescription.WorldClamp/WorldRepeat as
written, which carry MaxAnisotropy 1. The GL arm asks for the driver's own
GL_MAX_TEXTURE_MAX_ANISOTROPY twice over: ManagedGLTextureArray sets
GL_TEXTURE_MAX_ANISOTROPY on the image, and the two sampler objects its resident
bindless handles are built from (OpenGLGraphicsDevice.WrapSampler/ClampSampler)
set it again, which is the one that actually wins.
V6i-2 knew it was asking for 1 and said so in a comment -- "the world arm that
draws through these arrays is the next slice, and it is the one that can gate a
filtering change visually." That slice was V6j, the gate is V7, and this is it.
Retail settles the question rather than the GL arm settling it.
RenderDeviceD3D::SetDefaultD3DStates (0x005a3800) loops all sixteen sampler
stages and issues SetSamplerState(stage, 0xA, this->m_D3DCaps.MaxAnisotropy) at
0x005a4230. 0xA is D3DSAMP_MAXANISOTROPY and the argument is the device's
reported cap, not a setting -- so "as much anisotropy as this device has" is
retail's own rule, the GL arm is faithful to it, and asking for 1 diverged from
retail as well as from the shipping backend. No divergence-register row is owed
in either direction: this retires a Vulkan-only gap and lands on retail's value.
The fix asks for a ceiling rather than reading a limit back, because the pinned
RHI contract (plan section 3.3) carries no anisotropy field and is frozen. It
does not need one: VulkanGpuSampler already clamps MaxAnisotropy to
VkPhysicalDeviceLimits.maxSamplerAnisotropy, Vulkan guarantees that limit is at
least 16 wherever the samplerAnisotropy feature is supported -- which this
backend requires -- and 16 is where every desktop driver caps. The request and
the GL arm's read therefore land on the same number.
What it was worth, from the difference map at the same stop: the roof shingles
of both Holtburg cottages, which had been dense hatching across the whole
surface, and the stone courses of the near building are now black. Measured as
high-frequency energy (mean absolute neighbour difference, GL versus Vulkan) the
right-hand roof went from visibly blurred to a ratio of 0.999 and the wall to
1.023; every other textured region in the frame is between 0.99 and 1.02.
Grazing-angle surfaces are where anisotropy is the whole difference, which is
why a roof was the loudest thing in the frame.
2. THE SKY HAS TWO CLOCKS AND ONLY ONE OF THEM WAS PINNABLE.
ACDREAM_DAY_GROUP and the route's AcdreamCycleTimeOfDay presses pin the Dereth
date, which chooses the day group, the keyframe and the sun angle. The cloud
sheet does not read that clock: SkyRenderer accumulates TexVelocityX/Y against
DateTime.UtcNow minus its own construction time, by design, because retail's
clouds drift with real time regardless of the date. Two launches minutes apart
therefore cannot agree about where the clouds are no matter what the route does,
and the V6m smoke measured the cost -- 89% of its 18.52% sat in the top 240 rows.
ACDREAM_SKY_PHASE_SECONDS (RuntimeOptions.SkyAnimationPhaseSeconds ->
SkyRenderer.AnimationPhaseSecondsOverride) replaces that elapsed-seconds value
with a fixed one. Unset -- the default, and every ordinary run -- keeps the wall
clock, so nothing a user or the offline gate sees changes. The differential gate
forces it on both launches alongside MSAA and the day group; the offline gate
keeps its top-280 mask, because a same-commit GL pair still has the sun to
disagree about.
This is instrument determinism on the same footing as ACDREAM_DAY_GROUP, not a
workaround: it is one input to a UV offset, it is off by default, and no shipping
path reads it. The alternative on the table was -MaskTopPixels, which would have
permanently blinded the campaign's strictest instrument to the entire sky -- one
of the five surfaces the offline gate already cannot see. Rows 0-32 of the
Holtburg pair went from 23,090 differing pixels to 1,211, and what remains up
there is roof and portal rather than cloud.
WHAT THE SAME PAIR STILL SHOWS, unattributed and carried to the next commit: the
distant treeline, the player and the NPCs, and the animated portal. The portal is
phase and expected. The treeline is not filtering -- sharpness now matches within
5% and a shift search finds no sub-pixel offset -- and the two runs entered the
world at different last-logout positions (0xC95B0001 versus 0x09040008), so the
far-tier streaming history differed. That is the next thing to prove or refute.
Gates. Release build green. App tests 4,133 passed / 3 skipped against the
4,132/3 baseline (one new: the sky-phase parse). GL offline pixel gate against
the pre-change tree: 2.31e-05, 13 pixels of 563,200, inside the documented 9-31
band -- GL did not move. One offline Vulkan run with VK_LAYER_KHRONOS_validation
proven inserted by the loader: zero validation errors, zero warnings. Full
three-stop differential recorded at artifacts/v7-diff-c1.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
tools/run-backend-differential-gate.ps1 is V7's instrument, plus the route it
runs. It executes the SAME connected route twice - ACDREAM_RENDER_BACKEND=gl
then =vulkan - pairs the screenshots by name, compares each pair with
compare-screenshots at the plan's pinned tolerance 2 / fraction 0.001, and
prints one verdict table with a JSON report beside it.
ACDREAM_MSAA_SAMPLES=0 IS FORCED ON BOTH LAUNCHES. Plan section 5.5.16 measured
what leaving it on costs - 8.83% of the frame at 4x, essentially all of it
hugging foliage and silhouette edges, which is two drivers' sample patterns and
not a renderer divergence. Forcing it on one side only would be worse than
either. ACDREAM_DAY_GROUP is pinned on both, and the route additionally pins the
client-only time-of-day override so the Dereth clock cannot drift between two
launches minutes apart.
The desktop witness and its three guards are lifted from the repeat-run gate
rather than reinvented, because that gate learned them the hard way: a blank
frame reads back as a valid PNG (section 5.5.2), so a second instrument that
shares nothing with the renderer decides whether a run is worth comparing at
all; a locked screen or an overlapping window is caught by the grab's size; and
stray input into a foregrounded window moves the camera off the pinned stop, so
the client log is scanned for camera-affecting actions and the run is aborted
rather than reported. Both runs close through WM_CLOSE - a hard kill leaves ACE
holding the session about three minutes and the second launch is the one that
pays for it.
connected-backend-differential.route.txt is written for two-launch determinism,
which is stricter than either existing route needed to be: identity quaternions
on every teleloc so heading is pinned, no movement between arrival and capture,
and no checkpoint verb (the ownership ledger has its own gate). Three stops -
Holtburg town, an interior EnvCell at the Facility Hub, Aerlinthe's island and
water edge. The interior stop is the durable fix section 5.1 names for the
campaign's oldest coverage gap: no connected route has ever visited one, which
is why EnvCellRenderer had no automated coverage on either backend.
ONE SMOKE PAIR was run, on the first stop, and it is reported honestly rather
than tuned. GL versus Vulkan at Holtburg with MSAA off: 170,697 of 921,600
pixels differ, 18.52%, maximum channel delta 255. Attributed with a difference
map:
* 89% of it is in the top 240 rows. Masking the offline gate's top 280 rows
takes the pair to 11,480 of 563,200, 2.04%. That band is the scrolling
cloud sheet, which advances with WALL time and not with the pinned Dereth
clock, plus the treeline behind it.
* Masking the animated portal beside the character as well takes it to 6,190
of 529,450, 1.17%, mean channel delta 0.49. A portal's scrolling texture is
phase, like an emitter's age.
* What remains is thin outlines on silhouette edges throughout the frame,
plus the vitals readouts, whose stamina and mana genuinely advanced between
the two logins.
So the distance to V7's 0.001 is about 12x with the two known phase populations
removed, and V7 owns closing it. -MaskTopPixels exists for that conversation and
DEFAULTS TO 0: the gate is a strict identity check on the whole frame unless
someone deliberately asks otherwise, per section 7.1 rule 2.
Both files are ASCII with CRLF, matching the other tools. That is not cosmetic:
PowerShell 5.1 reads a BOM-less .ps1 as ANSI, so a UTF-8 em dash inside a
double-quoted string is a parse error, which is how the first version failed.
Gates. Release build green; App tests 4,132 / 3 skips. No product code changed,
so commit 1's pixel, connected and validation gates stand unchanged - and the
smoke run is this commit's own evidence, since it drove a complete connected
Vulkan session end to end with a graceful exit.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Erik