fix(VR): interior water submersion masks

[alandtse]

Summary by CodeRabbit

• Bug Fixes
  • VR underwater rendering now falls back to a system-derived water height when tile data is missing, improving mask correctness.
  • Per-eye camera-relative adjustments make underwater masks more stable and consistent across stereo views.
  • Engine water-query failures no longer produce incorrect default water values, yielding more reliable underwater visuals.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a VR fallback water-height source: shaders use SharedData::WaterSystemHeight when tile lookups return the "no water" sentinel, applying per-eye camera-relative Z offsets. CPU populates this field from player/TES water height when available and TryGetWaterData prefers cell->GetWaterHeight(...) if successful.

Changes

Cohort / File(s)	Summary
Shared Constant Buffer package/Shaders/Common/SharedData.hlsli, src/State.h	Replaced dummy padding with float WaterSystemHeight in the shared cbuffer/struct to expose a system-level water height (camera-relative Z, sentinel when absent).
CPU-side water computation src/State.cpp, src/Utils/Game.cpp	State::UpdateSharedData initializes and conditionally sets WaterSystemHeight from TES/player water height (converted to eye‑0 camera-relative Z) for VR fallback. Util::TryGetWaterData now uses cell->GetWaterHeight(...) when available and leaves w as sentinel on failure.
VR underwater mask shader features/Upscaling/Shaders/Upscaling/UnderwaterMaskUpscalePS.hlsl	When tile lookup equals NO_TILE sentinel, shader reads SharedData::WaterSystemHeight and recomputes per‑eye waterHeight using FrameBuffer::CameraPosAdjust.z offsets (eye 0 as reference) before proceeding with per‑eye mask logic; comments updated.

Sequence Diagram

sequenceDiagram
    participant CPU as CPU (State.cpp)
    participant GameUtil as Game Utils (TryGetWaterData)
    participant ConstBuf as SharedData ConstBuffer
    participant Shader as UnderwaterMaskUpscalePS

    CPU->>GameUtil: TryGetWaterData(position)
    alt GetWaterHeight succeeds
        GameUtil-->>CPU: cell water height (camera/world)
    else
        GameUtil-->>CPU: no-tile sentinel (-FLT_MAX)
    end

    CPU->>CPU: If VR & player underwaterCount>0\ncompute worldWater = player->GetWaterHeight()
    alt worldWater valid
        CPU->>CPU: WaterSystemHeight = worldWater - eye0.z
    else
        CPU->>CPU: WaterSystemHeight = sentinel
    end
    CPU->>ConstBuf: write WaterSystemHeight

    Shader->>ConstBuf: read tile water value (data.w)
    alt tile != NO_TILE
        Shader->>Shader: use tile-based per-eye waterHeight
    else
        Shader->>ConstBuf: read WaterSystemHeight
        Shader->>Shader: apply per-eye CameraPosAdjust.z (eye0 reference)
        Shader->>Shader: reconstruct per-eye underwater mask
    end

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix(VR): underwater mask while partially submerged #2062 — Modifies VR underwater-mask shader logic and SharedData water-height handling with per-eye adjustments.

Suggested reviewers

• davo0411

Poem

🐰
When tiles are gone and waters hide,
I nibble offsets, hop inside.
Eye-zero leads, the others follow,
Masks rebuilt beyond the hollow.
Splash—fallback saves our gentle waddle 💧

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: fixing VR interior water submersion masks by implementing a fallback mechanism for water height detection.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[github-actions]

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[github-actions]

✅ A pre-release build is available for this PR:
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[coderabbitai]

🧹 Nitpick comments (1)

package/Shaders/Common/SharedData.hlsli (1)

27-27: Keep sentinel terminology consistent across CPU and shader comments.

This comment uses -FLT_MAX, while the C++ side documents -NI_INFINITY. Consider using one term consistently (or explicitly noting they map to the same sentinel) to reduce ambiguity during debugging.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@package/Shaders/Common/SharedData.hlsli` at line 27, The shader comment for
the WaterSystemHeight field uses the sentinel value "-FLT_MAX" while the C++/CPU
side documents "-NI_INFINITY"; update the comment for WaterSystemHeight (and any
nearby shader comments) to use the same sentinel term as the CPU side (use
"-NI_INFINITY") or explicitly state they are equivalent (e.g., "-NI_INFINITY
(-FLT_MAX on shaders)") so TES::GetWaterHeight mapping is unambiguous across CPU
and shader code.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@package/Shaders/Common/SharedData.hlsli`:
- Line 27: The shader comment for the WaterSystemHeight field uses the sentinel
value "-FLT_MAX" while the C++/CPU side documents "-NI_INFINITY"; update the
comment for WaterSystemHeight (and any nearby shader comments) to use the same
sentinel term as the CPU side (use "-NI_INFINITY") or explicitly state they are
equivalent (e.g., "-NI_INFINITY (-FLT_MAX on shaders)") so TES::GetWaterHeight
mapping is unambiguous across CPU and shader code.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 0706e6b9-88e3-4d20-af7e-b01e7fe8debd

📥 Commits

Reviewing files that changed from the base of the PR and between df73cbb and 37686c2.

📒 Files selected for processing (3)

• package/Shaders/Common/SharedData.hlsli
• src/State.cpp
• src/State.h