ludic/docs/language/light/_section.md
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feat(light): render-quality tiers 3-4 — cones, falloff, soft shadows, gels, normals, day/night (#49)
The remaining lighting tiers from the original proposal, all extending the
deterministic accumulation core (light.ludic) — no new ECS plumbing:

- Light.spot: cone / flashlight lights (direction + spread degrees), with a
  self-contained integer atan2-in-degrees and a feathered edge.
- Light.falloff: a brightness-ramp exponent (1 linear, 2 quadratic, …) via
  repeated fixed multiply.
- Light.soft: soft shadows — an area-sampled light so an occluder edge fades
  through a penumbra instead of a hard cut.
- Light.gel + Light.clear_gel: colour cookies — a light gels from its centre
  colour to a rim colour.
- Light.normal + Light.clear_normals + Light.height: a normal G-buffer so
  surfaces shade by facing (N·L), not distance alone (tier 3).
- Light.time_of_day: a day/night ambient ramp from a single 0..1 value.

The engine lighting system (systems_light.ludic) consumes matching optional
Light2D fields — direction/spread/falloff/softness/gel — each defaulting off so
an older five-field Light2D lights exactly as before. Every tier is integer +
Q16.16 fixed, so scenes light identically on every run and headless.

Worked example + regression: examples/library/light_tiers.ludic (1 1 1 1 1 1 1 1 1).
Nine new docs/language/light pages. Full suite 76 passed, self-host C-free
fixpoint intact, no golden drift.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-31 16:35:41 +03:00

2 KiB

id title order
light Light 33

A software 2D light-accumulation pass over the framebuffer, run in a render phase after drawing the scene and before Screen.show. Light.ambient multiplies the whole scene toward a tint — the night/cave modulate that darkens everything so lights add mood back on top. Light.point accumulates a radial glow that falls off with distance and clamps per channel, and Light.occlude registers rectangles that block a light's rays to cast hard shadows (cleared each frame with Light.clear_occluders). Lighting is a rendering concern only — it never touches game state or replays — and it is fully deterministic (integer and Q16.16 fixed), so the same scene lights identically every run and in a headless render, keeping screenshots diffable. Colours are 0x00RRGGBB. Beyond the radial core, the pass carries the render-quality tiers: Light.spot cones, a Light.falloff exponent, Light.soft shadows (penumbra), Light.gel colour cookies, normal-mapped surfaces (Light.normal + Light.height) that shade by facing, and a Light.time_of_day day/night ramp — every one deterministic. This is the imperative surface; the engine also consumes Light2D/Occluder components automatically (a Light2D may carry optional direction/spread/falloff/softness/gel fields). Related: Screen, Color, Camera.