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gig-line/Docs/Architecture/04_solution_strategy.md
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zwitschi 71c7ca734b docs(arch): realism leads the quality list; performance moves to the end
Owner decision: prioritise realism, keep the performance target but put it last.
Re-applied on a branch after the first attempt landed directly on main (reverted
there; see b8209ce).

- Quality goals (01 + combined architecture.md): 1 visual realism, 2 geographic
  fidelity, 3 walkability/usability, 4 reproducibility/portability, 5 provenance,
  6 performance efficiency.
- Quality requirements (10 + combined) reordered to match, with two realism
  requirements added (a façade reads like the photographs; placement within ~1 m)
  and the scenarios renumbered so QS-1 is the reference comparison, QS-9 the frame
  rate.
- Guard on both documents so the order cannot become an excuse: performance is a
  floor, not a preference - 60 FPS at 1440p without frame generation must be met at
  every release; if realism cannot fit, cut the realism scope deliberately and
  record it, never the frame rate. Walkability outranks realism in one direction: a
  block you fall through is not a demo.
- Solution strategy and 'quality achievement' lead with realism and describe
  performance as a budget, not a driver.
- Docs/release-checks.md: the performance check is the last section and the per-
  version check list now opens with realism and closes with performance.
- ROADMAP gains a 'Quality priority' section; AGENTS.md gains the tie-break rule
  beside the existing scope-cutting rule.
2026-11-08 20:37:32 +01:00

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Markdown

# Solution Strategy
## Technology decisions
- **Unreal Engine 5.8.4** for rendering, World Partition, physics (Chaos), and the Enhanced Input system. Chosen for its Linux support, open C++ source, and real-time rendering quality.
- **Blender 5.2 LTS** for all 3D modelling, UV work, and collision mesh authoring. Driven headlessly via `bpy` Python scripts, not MCP.
- **QGIS 4.2.3** for geographic data cleanup, coordinate conversion (EPSG:26911), and DEM preparation.
- **Blosm 2.7.28** for OSM building and street blockouts inside Blender (layout data only — not authoritative façade, height, or pavement detail).
- **MPFB 2.0.18** for human base meshes and baked materials (NPCs in `0.2.0+`).
## Top-level decomposition
The system is a single Unreal game module (`GigLine`) with no plugins beyond `EnhancedInput`. Content is organised by domain under `/Game/Hollywood/`:
- `Site/` — terrain, road, sidewalks, kerbs, crossing markings, site materials
- `ElCapitan/` — hero façade mesh and materials
- `Frontage/` — south-side block building meshes
- `North/` — north-side building meshes
- `Input/` — Enhanced Input actions and mapping context
All modelling and geographic processing live outside the game project in `Art/`, `Geo/`, and `Tools/`. The `Game/` directory contains only engine-ready content and C++ source.
## Quality achievement
- **Realism first**: reference photography and measured data drive every façade decision; renders are compared against the photographs with `Tools/visual_loop.py`, and a façade is built from the shared 4.96 m module kit so the street wall reads consistently. Materials are authored in Unreal with world-aligned generated textures, and lighting is fixed daytime so a shot is comparable between runs.
- **Performance as a budget, not a driver**: dynamic-only lighting (no build step, no static shadow maps), world-space-noise materials (cheap procedural variation), minimal overdraw for street-level geometry, and a 60 FPS at 1440p floor that every release must meet. It closes the quality list because it constrains how much realism fits, not what the block should look like.
- **Walkability**: complex-as-simple collision on terrain (C++ helper forces the flag on the asset), block-all collision on every site mesh, swept transect QA verifies zero raycast holes.
- **Fidelity**: geographic data verified before modelling (footprints, bounds, DEM); building placement checked against street mesh, never in isolation; reference photography drives façade work.
- **Reproducibility**: pinned toolchain in `Docs/toolchain.md`, named export presets, `Tools/check-lfs.sh` gate, fresh-checkout build procedure in `Docs/build.md`.