Design for raising the renderer from geometrically-correct-but-flat to
Gargantua-reference fidelity. Four user-selected traits:
- HDR color + ACES tone mapping (Rgba16Float offscreen, Narkowicz fit)
- Multi-pass HDR bloom (bright-pass → down-pyramid → up-pyramid → composite)
- Domain-warped FBM disk texture (replaces two-sine noise)
- Anti-aliasing via render_scale + gaussian-speck stars
All quality options configurable via a dedicated egui Quality panel,
with tiered web defaults (Low bloom, no MSAA/star-AA) vs desktop (High).
BloomQuality::Off falls back to the original LDR path for WebGPU
browsers without float-filterable support.
Geodesic integrator (deriv/rk45_step/is_captured_rk45) untouched —
the physics.rs mirror contract is unaffected. No new tests.
