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feat(contract): pixel-water sub-surface — the COND-07 binding seam - #78
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RFC-PIXEL-WATER phase 1: lock the binding contract before anything downstream is written. The condenser's reservoir needs three colour ramps, wave/ripple tuning and up to eight live drop impacts — 8x the 32-byte `MaterialUniforms` block that EVERY sprite carries inline on `SpriteVisual`. Widening that block would make `.none` sprites pay for water, so the payload rides its own optional draw decl instead: drawTextureProPixelWater(tex, src, dest, origin, rot, tint, PixelWaterDraw) `PixelWaterDraw` is a flat, by-value `extern struct` — the same reinterpret-safe shape as `MaterialUniforms`/`PostPass`, so no pointer and no generational handle crosses the assembler-generated marshal seam between differently-pinned packages. Its layout is locked at 16 vec4s (256 bytes, u32 header first) by comptime size/offset assertions, which is the phase-1 exit the RFC asks for: a silent field insertion breaks the build rather than misreading uniforms on a GPU. `MaterialEffect.pixel_water` is the capability identity, so the renderer's warn-once table, the provider manifest `.capabilities` mirror and negotiation all work unchanged. It is APPENDED (tags 0..4 keep their values) and it is the one effect whose support is NOT implied by declaring `drawTextureProMaterial`: `materialCapabilities` and `Backend(Impl).materialSupported` additionally require the water decl. Without that, every backend written before this sub-surface existed would start advertising water it cannot draw. Unsupported degrades to a plain `drawTexturePro` — the authored STATIC reservoir fallback. Purely additive and `@hasDecl`-gated, so `DRAW_CONTRACT_VERSION` does not bump and no existing backend is rejected. The mock opts in and records the whole resolved payload, so gfx/engine can assert level/time/ripple state deterministically with no GPU — and tell the real effect from its fallback apart (water calls vs draw calls). Refs: labelle-bgfx#100, labelle-engine#879 Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Included review availability: 7 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 10 reviews per hour. 📝 WalkthroughWalkthroughThe change adds an optional ChangesPixel-water rendering
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant Caller
participant Backend
participant MockBackend
participant PlainDraw
Caller->>Backend: drawTextureProPixelWater(water)
Backend->>Backend: Check pixel-water capability
Backend->>MockBackend: Record texture, tint, destination, and water
Backend->>PlainDraw: Use ordinary draw when unsupported
Merge Risk: ⚪ Minimal · up to Pixel-water rendering preserves its dedicated payload when supported and safely falls back to normal textured drawing when unsupported. No actionable current-head risk remains. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@src/backend_contract.zig`:
- Line 308: Update the backend contract around the pixel_water enum and
materialSupported so existing backends with exhaustive switches remain
source-compatible; either bump and coordinate the contract version for this
breaking enum addition, or represent pixel-water support without extending the
existing exhaustive enum, including the corresponding MockBackend handling.
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| /// `drawTextureProMaterial` does NOT imply support — see | ||
| /// `materialCapabilities` and the pixel-water sub-surface below. | ||
| pixel_water, | ||
| }; |
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When a caller passes Material{ .effect = .pixel_water }, Backend.drawTextureProMaterial still forwards it whenever Impl.drawTextureProMaterial exists and the implementation omits the optional fine-grained probe, even when the backend has no drawTextureProPixelWater declaration. This bypasses the new family-specific capability gate and can send tag 5 with an unrelated 32-byte uniform block into a pre-water backend. Make the generic wrapper consult Backend.materialSupported(material.effect) or explicitly degrade .pixel_water so this effect can only use the dedicated draw API.
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Review found a real hole in the first commit. The family gate covered
`materialSupported` and `materialCapabilities`, but NOT the generic
`drawTextureProMaterial` wrapper — so a backend that declares the material
decl and OMITS the optional `materialSupported` probe would have had
`Material{ .effect = .pixel_water }` forwarded straight to it. That hands a
pre-water backend tag 5 alongside an unrelated 32-byte `MaterialUniforms`
block, and the fine-grained probe cannot catch it precisely BECAUSE that
backend has none: omitting the probe means "I support every built-in".
`.pixel_water` is now gated out at the coarse level, next to `.none`: it
never rides the generic path whatever a backend declares, and reaches a
backend only through the dedicated `drawTextureProPixelWater` API its
payload was shaped for.
The regression test asserts the MECHANISM, not the outcome: a fixture
backend records the effect tags that actually entered its material decl,
so the test fails if tag 5 arrives even though the plain-draw counter
would look right either way. Verified by removing the gate — the test
fails with `expected 1, found 2`.
Also stops describing the change as "purely additive". Appending a tag to
`MaterialEffect` is source-breaking for any backend with an exhaustive
switch; the `@hasDecl` gate governs dispatch, not compilation. The
`*_CONTRACT_VERSION` numbers still do not bump, but now as a recorded
judgement rather than a claim that nothing broke: `DRAW_CONTRACT_VERSION`
feeds the assembler's all-or-nothing build gate, so bumping it would
reject every backend — including the four with no material switch at all —
to announce a break that already surfaces as a precise compile error in
the two that have one. The per-backend audit is recorded in the header.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XBGRLojiysEr5zy1U5mbP6
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Both findings addressed in @chatgpt-codex-connector — P1, confirmed and fixed. This was a real hole. The family gate covered The regression test asserts the mechanism rather than the outcome: a fixture backend records which effect tags actually entered its material decl, so it fails if tag 5 arrives — a plain-draw counter alone would have looked correct either way. Verified by removing the gate: @coderabbitai — half agreed, half pushed back, and the docs now say so. You're right that this is not "purely additive": appending a tag to I'm not bumping The alternative you offered — representing water capability without extending the enum — was considered and rejected upstream: The break is already handled downstream: labelle-toolkit/labelle-sokol#20 adds the decline arms, and labelle-toolkit/labelle-bgfx#101 implements the effect. Suite: 213/213. |
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Tip For best results, initiate chat on the files or code changes. 🧩 Analysis chain🏁 Script executed: #!/bin/bash
set -euo pipefail
git show --stat --oneline 9d7dfa4
printf '\n--- changed files ---\n'
git show --format= --name-only 9d7dfa4
printf '\n--- backend contract outline ---\n'
ast-grep outline src/backend_contract.zig --items all --type function,method,enum,struct --match 'MaterialEffect|materialSupported|drawTextureProMaterial|drawTextureProPixelWater'
printf '\n--- relevant contract code ---\n'
rg -n -C 12 'DRAW_CONTRACT_VERSION|MaterialEffect|materialSupported\s*\(|drawTextureProMaterial\s*\(|drawTextureProPixelWater\s*\(' src/backend_contract.zig
printf '\n--- relevant regression-test code ---\n'
rg -n -C 12 'effect tags|effect_tags|drawTextureProMaterial|pixel_water|expected 1' test/root_test.zig
printf '\n--- commit patch for relevant files ---\n'
git show --format= --unified=35 9d7dfa4 -- src/backend_contract.zig test/root_test.zigLength of output: 60380
The new regression test uses a backend without The documentation now correctly identifies the exhaustive I inspected the code changes. I did not execute the test suite in this environment. ✏️ Learnings added
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One feature since v1.31.0, so a minor bump: * #78 — the `pixel_water` binding seam for the COND-07 condenser (labelle-bgfx#100, RFC in labelle-engine#879). `MaterialEffect.pixel_water` is the capability identity; the payload rides its own optional decl `drawTextureProPixelWater(..., PixelWaterDraw)` rather than widening `MaterialUniforms`, which every sprite carries inline. `PixelWaterDraw` is a flat by-value `extern struct`, layout-locked at 256 bytes / 16 vec4s by comptime size/offset assertions. READ THIS IF YOU MAINTAIN A BACKEND. Appending a tag to `MaterialEffect` is SOURCE-BREAKING for any backend with an exhaustive `switch` over it: that switch stops compiling against this core until it gains a `.pixel_water` arm. The `@hasDecl` gate governs dispatch, not compilation, so it does not prevent this. Known affected, both already handled: labelle-sokol (#20, declines the effect) and labelle-bgfx (#101, implements it). labelle-gfx needs one arm in a test. raylib / sdl / wgpu / null have no material switch and are unaffected. No `*_CONTRACT_VERSION` bumps. That is a recorded judgement, not an oversight: `DRAW_CONTRACT_VERSION` feeds the assembler's all-or-nothing `targets_draw_contract` build gate, so bumping it would reject EVERY backend — including the four that are genuinely unaffected — to announce a break that already surfaces as a precise compile error in the two that are. The reasoning and the per-backend audit are recorded in `backend_contract.zig`. Support for `pixel_water` is NOT implied by declaring `drawTextureProMaterial`: it is the one effect additionally gated on its own decl, in both `materialCapabilities` and `Backend(Impl).materialSupported`, and it never rides the generic material draw path. Without that, every backend predating this seam would advertise water it cannot draw. Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XBGRLojiysEr5zy1U5mbP6
Phase 1 of RFC-PIXEL-WATER — lock the binding contract and baseline — for labelle-bgfx#100 (animate the COND-07 condenser). Contract only: no shader, no gfx retention, no engine authoring.
The problem this settles
The reservoir's per-instance state is three colour ramps, wave/ripple tuning and up to eight live drop impacts — 8x the 32-byte
MaterialUniformsblock that every sprite carries inline onSpriteVisual. Widening that block makes.nonesprites pay for water.So the payload rides its own optional draw decl:
PixelWaterDrawis a flat, by-valueextern struct— the same reinterpret-safe shape asMaterialUniforms/PostPass. No pointer and no generational handle crosses the assembler-generated marshal seam between differently-pinned packages, which is what the RFC warns against.MaterialUniformsis byte-identical and the four shipped effects keep their tags.Locked layout (the phase-1 exit)
16 vec4s, 256 bytes, u32 header first, so a backend maps it onto uniform registers without repacking. Held by comptime
@sizeOf/@offsetOfassertions plus a runtime mirror test — a silent field insertion breaks the build instead of misreading uniforms on a GPU.mask_texture,reflection_texture,logical_width,logical_height,grid_pixels,ripple_count,flags,_reserved_u0(u32)deep,surface,highlight(PixelWaterRgba, linear 0..1)level,time,wave_amplitude_pixels,wave_period_secondsdistortion_pixels,reflection_opacity,ripple_duration_seconds,ripple_radius_pixelsripple_strength_pixels+ 3 reservedripples: [8]PixelWaterRipple(x,start_time,strength)PIXEL_WATER_MAX_RIPPLES = 8is fixed, not a slice: it keeps the value flat and gives the shader's ripple loop a comptime trip count, which ESSL 3.00 / WebGL2 need.timeis simulation seconds and the surface defines a ripple's y — that is what keeps an impact attached to a rising surface while the condenser fills.The capability trap this closes
materialCapabilities' default is "declareddrawTextureProMaterial⇒ supports every built-in". Appendingpixel_watertoMaterialEffectnaively would make every pre-existing backend advertise water it cannot draw.pixel_wateris therefore the one effect gated on its own decl, in bothmaterialCapabilitiesandBackend(Impl).materialSupported. The two families gate independently (material-only, water-only and neither are each covered by a test). Unsupported → plaindrawTexturePro, i.e. the authored static reservoir fallback.Purely additive and
@hasDecl-gated ⇒DRAW_CONTRACT_VERSIONdoes not bump; no existing backend is rejected.Mock
Opts in and records the whole resolved
PixelWaterDraw, so gfx/engine can assert level/time/ripple payloads deterministically with no GPU — and distinguish the real effect from its fallback (water calls vs draw calls).Downstream compatibility matrix (audited, follow-ups)
Exhaustive
switches overMaterialEffectthat will need a.pixel_waterarm when they bump this pin:src/gfx/material.zig(5 sites:materialSupported, uniform size, sampler count, pipeline select, coverage). Needs.pixel_water => false/unsupported arms; no shader.src/gfx/texture.zig(3 sites),src/gfx/programs.zig(programForEffect). This is where the effect is actually implemented (#100 phase 4).test/material_batch_cost.zigonly.pixel_waterunsupported.Validation
zig build test— 212/212 pass (was 209; +3 water tests, 1 updated capability count).zig buildclean.zig fmt --checkclean on every touched file (the 8 reported files are pre-existing and untouched here).Need help on this PR? Tag
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