ludic/docs/language/light/_section.md
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feat(rendering): add Light.* — deterministic 2D light accumulation with hard shadows (#4)
A software light pass over the framebuffer, run in a render phase after drawing
the scene: Light.ambient multiplies the scene toward a tint (night/cave mood),
Light.point additively accumulates a radial glow with linear falloff clamped per
channel, and Light.occlude / Light.clear_occluders cast hard shadows by blocking
a light's rays against rectangular occluders. Integer + Q16.16 fixed throughout,
so a scene lights identically every run and in a headless render (diffable).

Engine in runtime/native/light.ludic, spliced on demand (g_uses_light) like the
regex/query runtimes; namespace wired in emit_call.ludic. Ships issue #4 tiers 1
(ambient + additive radial lights) and 2 (hard shadows). Normal-mapped sprites,
soft shadows, a day/night directional light, and auto-consuming Light2D/Occluder
components are follow-ups (the auto-system hook is tracked by #43).

- runtime/native/light.ludic: the light-accumulation engine (isqrt falloff,
  segment/occluder shadow test, ambient modulate)
- examples/library/lighting.ludic: 14 pixel-readback assertions
- docs/language/light/: Light.ambient/point/occlude/clear_occluders
- tools/x/test.ludic: lighting.ludic in the regression suite

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-31 14:07:19 +03:00

1.3 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. This is the imperative surface; consuming Light2D/Occluder components automatically, normal-mapped sprites and soft shadows are planned follow-ups. Related: Screen, Color, Camera.