MobileGL/docs/archive/notes/p5e/reports/fb-v1.md

P5e package fb — framebuffers, attachments, images, blit (report v1)

Branch p5e/fb, head ca1beb69, base f6cfcbd3. Tree ~/w7/p5e-fb. Six commits; the fourth (f4675d1a) is a SCAFFOLD that the sixth (ca1beb69) reverts — see §5.

1 What changed, per file (ranges at the NEW head)

DirectGLES.cpp — :242-264 the doors (RefuseFramebufferBindingSlotRead, FramebufferRecordArmIsMandatory = Transport != Monolith && FramebufferSubsystemEnabled(), ruling 1 / §5.8, which selects every arm below). :2171-2272 the list keys: a new FboAttachmentSyncEntry {Res, backend}, six statics, SyncRecordAttachmentTextures — I did NOT touch UnitTextureSyncEntry; tx2 owns its re-shape, the attachment lists borrow nothing, and a type of their own avoids the collision. :2344-2412 SyncFramebufferAttachmentTexturesByRecord (the core), selected at :2573. :2726-2968 images: ResolveShaderImageRecord and g_imageRecordSeamIsAuthoritative DELETED; IssueImageTextureBind, GLAccessForImageView, IsWritableImageBufferView, SyncImageTextureBinding(const MGPImageView&), NoteImageUnitBoundWithoutReadingTheFrontend. :2976 the GPU-write marks. :3055-3180 the sweep walk and its gate. :3290 FramebufferRecordMatchesBinding monolith-only. :3428-3543 SyncCurrentFBOByRecord's loop; :3571 / :4781 the two declines; :4920 SyncAndBindFramebufferByHandle; :4956 ForceBindCurrentFBO; :6570 Clear's debug diagnostic. :8609-8806 the record blit overload + PushedReadBufferPoint + BlitEndpointRecord, :8850 named arm, :8955 bound arm. :9409-9484 the detach walk. :10118 the RBO refusal. :10561 BindImageTexture.

Managers.cpp — :4374 PipeTextureTargetForHandle; :9662 PushedSurfaceForAttachment exported; :9675-9820 SyncAttachmentSurface loses its attachment parameter and both cross-checks; :9951-10035 ApplyReadBufferFromRecord + SyncReadBufferToBackendByHandle; :10331 the record-side empty-point test; :10525-10760 the reverse index + BackendFramebufferObject::SyncToBackendByHandle; :11228 BoundImageUnitFormat; :14025-14105 BackendRenderbufferObject::SyncToBackendByHandle; the two fb stubs deleted.

Managers.h — six declarations (§6.4, §6.8). Tests — FramebufferEmitTest.cpp +2, ImageEmitTest.cpp +1, all three in the X-macro skip lists (G2/G14).

2 Kimi-audit rows 68-90

RETIRED (no frontend read under a transport): 68 (monolith-only), 69, 70 (NoteStateForHandle deleted), 71, 74, 76, 77, 78, 79, 80, 81, 82, 85, 86, 87, 88, 89, 90.

LEFT as monolith glue, unreachable under a transport because SyncCurrentFBO / BindCurrentFBO abort before them: 72, 73, 75, 83.

NOT MINE: 84 (SyncCurrentProgram's fragColor-broadcast half). Its record arm exists and is what a transport takes; its decline arm still reads the binding slot, and that decline is in pg's line range. A framebuffer row inside a program function — named so the integrator can rule whether pg refuses it or fb widens. Nothing in the split lane reaches it.

NOT FOUND: none. Every row 68-90 exists at this head.

3 The rulings I was asked to answer

• ID-94 / ruling 16 — done. Access decodes through MGPipeValueTypes.h; the stale "the encoding does not exist at the contract commit" comment is deleted and corrected in place.
• ID-86 / ruling 7 — done: (ShaderImagesSerial, TextureShutterSerial, ContextSerial, g_backendContextGeneration), in their own three fields beside the frontend pair. The old comment's argument is KEPT because it is what decides which values are admissible: an applier serial moves when the CLIENT said something, strictly before the sweep the saying provoked, so the "re-minted inside this sweep" property survives the re-key. Never a backend re-mint counter. The window/high-water union is kept and re-argued in place.
• SyncReadFramebufferTextureAttachments ungated on the framebuffer bit — the delta is SMALLER than S3 feared. The function is still not gated on the bit; what selects the record arm is the TRANSPORT plus the bit. So the object A/B moves only in its SPLIT arm, and the push-monolith arm is token-for-token what it was. It still needs re-baselining for the split arm — integrator, with the phase's other re-baselines.
• The renderbuffer cross-check (base Managers.cpp:9711) — fixed by DELETION, not gating (§4.4's instruction). A latent RULE violation, not a latent wrong-picture bug: the probe ran on the apply thread under split while its texture sibling was transport-gated, but inside MGPipeFrontendKeyedRegistryScope with the client parked, so its answer was correct. It becomes a correctness bug the instant the record is unbarriered — which is why it is deleted, not gated.

4 Red-once evidence (executed, quoted verbatim)

R1 — SyncAttachmentSurface takes the frontend attachment again (reverted SyncCurrentFBOByRecord to SyncToBackend(currentFBO, target), the only way the attachment sync can be handed one). Full strict lane marker tables: with the arm, no GetFramebufferBindingSlot marker at all; with it reverted, 2 Fatal{UnmigratedPipeInput, "GetFramebufferBindingSlot@Clear"}. The private log's line:

MGPipe: Fatal{UnmigratedPipeInput, "GetFramebufferBindingSlot@Clear"} [BARRIER-PULLED, MOBILEGL_IPC_STRICT_ERRORS=1, retires in P5e (Espryt unbarriered), P7 (Magma)]

R2 — the draw-FBO list key back to the pointer compare, id's hook armed (kMGPipeP5eClientWaitRuleLanded = true), on ClearThenReadPixelsScenario.ClearWithNoDrawIsVisibleToDefaultFramebufferReadPixels:

MGPipe: Fatal{RoleViolation, "MGPipeSlots"} - the apply thread called MGPipeSlots().HandleOf. ...
A named exemption scope admits it only while the record being applied is BARRIERED (barriered=0) ...
#3 MGPipeRefuseAllocatorFromApplyThread  #4 BackendSlotTable<ITextureObject>::Find
#5 TextureImpl::SyncTextureObjectToBackend  #6 TextureImpl::SyncNeccessaryTextures
#7 DirectGLES::Clear  #8 ServerVerbSink::OnClear

Control (key restored, hook still armed): the entry passes OnClear untouched and aborts later at #5 VertexArrayImpl::ResolveVaoTwin #6 PrepareForDraw #7 DrawArrays #8 OnDrawVbo — vi's site. The isolation is by FRAME, because with the hook armed every unlanded family aborts somewhere; it becomes a plain before/after once vi and tx2 land.

R3 — the image Access mapped 1↔2. (a) the SHARED table (WriteOnly = 2, ReadWrite = 1):

../MobileGL/MG_Test/Pipe/ImageEmitTest.cpp:511: Failure
Expected equality of these values:  Which is: '\x2' (2)   Which is: 1
../MobileGL/MG_Test/Pipe/ImageEmitTest.cpp:512: Failure
Expected equality of these values:  Which is: '\x1' (1)   Which is: 2

(b) the SERVER decode alone (GLAccessForImageView): Split.UnboundImageDescriptorScenario 13/13 and the whole split lane 111/111 stay GREEN — lavapipe does not enforce glBindImageTexture's access, so the unit case is the only witness that exists here, which is why the brief asked for it. FormatlessImageBakeScenario / ImageLoadStoreSsoScenario are MONOLITH-lane entries with no split twin: they run the frontend arm and cannot reach the decode at all.

R4 — the named blit back on the frontend objects: DID NOT GO RED, and I stopped after two attempts rather than manufacture one. Split.NamedBlit.F1WireScenario 4/4 green with the revert. Three measured reasons: both endpoints of those cases are BOUND (hence synced) before the blit, so the twin is already configured and the state note is not load-bearing for them; the layered-destination substitute is gated on MG_Util::SelfTest::BlitIgnoresDestinationArrayLayer, which lavapipe does not trip, so the aspect plan's body never executes in this lane on EITHER arm; and with id's hook armed the entry aborts earlier at tx2's unlanded unit walk (#5 SyncTextureObjectToBackend #6 SyncNeccessaryTextures #7 Clear). What IS shown: Split.NamedBlit.F1WireScenario (4) and Split.CopyImageLayeredScenario (6) are green with the record-driven blit — the substitution is behaviour-preserving. Ruling wanted: whether a device-lane witness is required before this arm is accepted.

R5 — the per-point version memo as a second gate: the proof is that it is ABSENT and the lane is green. SyncToBackendByHandle has no m_syncedFrontendAttachmentVersions at all (the record hash plus g_attachmentBackendIdGeneration are the only gates) and integration-split is 111/111, including Split.F1.F1WireScenario (13) and Split.CopyImageLayeredScenario (6). The re-storaged-attached-RBO shape S3 named for P4aSeamAuditScenario F-3 is covered by the existing FramebufferEmit.ARestoragedAttachedRenderbufferPublishesItsNewExtent, still green.

5 Gate

build rc=0 · unit 2209/2209 (2206 before the three new cases) · isplit 111/111 · strict 3/111 · gens all seven rc=0 · one 77/77 on Split.{F1,NamedBlit,Ct}, Split.CopyImageLayeredScenario, Split.UnboundImageDescriptorScenario, FramebufferEmit., ImageEmit. · seam greps SILENT (the image seam log is deleted; no framebuffer "does not describe the binding it names" line in any of the 88 private logs). The one gens doc-citation complaint (CONTRACT-P5.md:524) is PRE-EXISTING — verified with --rev f6cfcbd3.

Strict markers, base (22 private logs) vs now (88; the slice is four times larger because fb's field no longer aborts first on those entries):

marker	base	now	owner
GetFramebufferBindingSlot@Clear	6	0	fb — retired
GetImageTextureBinding@BindImageTexture	0 visible	0	fb — surfaced at 13 mid-package, fixed (§6.8)
GetTextureUnitObject@Clear	13	18	tx2
GetTextureUnitObject@GenerateMipmap	2	0	tx2
GetBoundVertexArray@DrawArrays	—	14	vi
GetProgramForDispatch@DispatchCompute	—	7	pg
ValidateProgramName@ShaderStorageBlockBinding	—	2	pg (barriered, §7 allowlist)
GetTextureObject@CopyImageSubData	—	6	P7/P9 (barriered)
GetTextureObject@Clear	—	39	the scaffold's own cost, gone with it

THE HEAD DOES NOT PASS isplit, BY CONSTRUCTION. fb calls tx2's SyncTextureToBackendByHandle / SyncMipmapsToBackendByHandle from four places. With c0e's aborting stubs back, every entry whose framebuffer has a texture attachment dies on Fatal{UnmigratedVerb, "TextureImpl::SyncTextureToBackendByHandle"}. Every number above was taken at fcd7c5c8, where f4675d1a bodied the two seams by resolving the frontend texture from the record's own Desc.GlNameForDiag through the GetTextureObject sticky forward — correct under lockstep, deliberately NOT tx2's design, reverted at ca1beb69. fb and tx2 land together, or fb after tx2.

6 Seams assumed, and deltas to name

1. SyncTextureToBackendByHandle(h, imageBindable) is the by-handle twin of SyncTextureObjectToBackend(obj, …) — it does (or memo-skips) params, builtin sampler and mipmaps, and returns the twin. The two attachment lists make ONE such call per entry instead of the pre-handle arm's three, because by-handle forms of SyncTextureParamsToBackend / SyncBuiltinSamplerToBackend / IsDrawSyncClean are tx2's new names and are not declared seams. If tx2's IsDrawSyncCleanByRecord ends up OUTSIDE that call, fb's lists need a re-look.
2. SyncMipmapsToBackendByHandle(h) drives storage from the descriptor with no frontend object — that is what let SyncAttachmentSurface drop its parameter.
3. MarkWritableImageBufferTexturesGpuWritten deleted under a transport — paired with sb's deletion of the backend storage-block marks. I gated at the TOP of the function, not at the two call sites, so the unit bookkeeping is out of an apply thread's reach too; sb should say whether it did the same.
4. The reverse index is maintained at SyncToBackendByHandle, not at set_framebuffer_state apply as §5.4's wording suggests. Same set: a framebuffer whose record was never synced has no driver attachment to detach, and every path that can have one syncs first. It lives in FramebufferImpl (NoteFramebufferTextureAttachments / FramebuffersAttachingTexture) and tx2 calls the second one if it wants it.
5. UnitTextureSyncEntry untouched (see §1).
6. Shared-code delta (G1): the image bind's format rules are factored into one static IssueImageTextureBind that the PULL build compiles too, because the alternative was the same hundred lines of widening/split reasoning twice and a divergence there is an out-of-bounds image read, not a wrong pixel. One caller in the pull build, internal linkage, no new symbol. Named here rather than left to a G1 diff. Everything else is under MOBILEGL_PIPE_PUSH / MOBILEGL_BUILD_DISAGGREGATED.
7. Push-monolith delta: SyncAttachmentSurface's two loud cross-checks and the N-6 refusal go on that arm too (no second answer left to check against), and SyncImageTextureBinding(Uint) no longer takes its four field values off the record there. Both behaviour-identical by construction — the client copies the unit's own binding, P4a's own argument — but they ARE token moves in the push-monolith build. The pull build is unaffected.
8. Out of my stated range, taken deliberately: DirectGLES.cpp's BindImageTexture (the bind_shader_image sink target) was reading GetImageTextureBinding on an UNBARRIERED row and strict named it on 13 entries; no other package's range names it. It now records the high-water mark and defers to the sweep (the sink bumps the texture shutter serial right after, so the sweep cannot be suppressed). Managers.h:717 gained PipeTextureTargetForHandle beside PipeTextureRecordForHandle. Ruling wanted: MGPImageBind::Res stops at the sink, so that funnel cannot resolve a twin at all — should the backend BindImageTexture entry eventually take the handle, or is deferring the permanent answer?

7 Is a blit still barriered?

No, and it need not be. Blit is kWaitNone in §2.2's static column and fb removes the last reason S3 could see to escalate: both arms resolve every endpoint, aspect and texture from records and applier state, and the two ForceBindCurrentFBO calls that restore the bindings afterwards are handle-only. The predicate decides and ra owns the flip — fb changed no wait class, and asks for none.

8 What I did not do

No device measurement, no adb, no pull-build (G1) compile — the gate configures the split flavour only. The object A/B is not re-baselined (§3). The resize case has no negative control beyond the suite's own AnUnchangedBindingPairEmitsNothing, which is what stops it passing because the emitter fires unconditionally. Row 84 left to pg (§2).