benilla-octo/LIGHTING.md

benilla-lighting

A dynamic light and shadow system for benilla, the Rust + Bevy reimplementation of the 1.12.1 client. This branch is upstream benilla (merged at fd386e75) plus the lighting work, the enhanced water module and volumetric fog, and nothing else. It needs no data changes: everything is derived from what a 1.12 install already carries (WMO MOLT lights, MOCV vertex colour, portals, M2 particle emitters, Light.dbc).

Everything here is a departure from the reference client's look, so every lane has a live cvar and most can be switched off. Code is tagged MONKEY (<topic>) with the rationale and the measurements behind each constant.

What it does

Lane	What you see	Main switch
Sun shadows, characters	real silhouettes for units instead of the oval blob	characterShadows
Sun shadows, world	trees, buildings and alpha-tested foliage cast; baked terrain shadows step aside	worldShadows
Dynamic interiors	WMO rooms are lit per fragment by their own fixtures with a soft falloff, gated per room so light does not leak through walls	interiorLight, interiorRoomGate
Synthesised lights	torches, braziers, lanterns, campfires and lampposts emit a light in the colour of their flame, with flicker	fireLightGain, fireFlicker
Torch shadows	cube-map shadows from point lights onto buildings, models and terrain, with a contact-hardening penumbra and a shadow floor	interiorShadows, exteriorShadows, torchShadowStrength, interiorShadowSoft
Daylight and doorways	calibrated fixtures at doors, windows and open boundaries carry daylight into a room, and doorways between rooms bleed light	interiorDaylight, env WOW_DAYLIGHT, WOW_BLEED
Spell and firework lights	fire, holy and fel effects light their surroundings for their lifetime; frost, nature, arcane and shadow do not	spellLightGain, env WOW_SPELL_LIGHT=0
Moon shadows	at night the same shadow rig re-aims at the moon and casts a faint shadow; dims only the night sky term, never point lights	moonShadowStrength
Ground-effect spells	Flamestrike, Rain of Fire, Consecration, Flare and fire traps light the ground for their duration; frost and nature areas stay dark	spellLightGain
Volumetric fog	near-field haze that converges on the zone fog colour (clear within 10 yd, full by 150 yd; mistier at dawn and in bad weather, faint indoors) and sun/moon light shafts through gaps, sampled from the shadow map; own fullscreen pass after the main pass (benilla-app/src/volumetric_fog.rs)	Advanced Graphics → Volumetric Fog (Off/Low/High), cvar volumetricFog, env WOW_VOLFOG=0|1|2
Sky dithering	a faint screen-space dither in the FFXGlow combine so smooth sky and fog gradients do not band (MONKEY p0; was env-only)	Advanced Graphics → Sky Dithering, cvar skyDither 0/1 (default 0, Graphics preset High = 1), env WOW_DITHER=1 still forces it on; bridge in benilla-app/src/monkey_gfx.rs
Night and interior level	global dimming of the night sky term and of interior ambient	nightGain, interiorGain, interiorBakeFloor

Players reach all of it from Options -> Advanced Graphics (a Lighting Quality preset Off / Low / Medium / High plus the individual rows; Off is the original client look). The dev build has a panel for all of it: Ctrl+Shift+D → Lighting & shadows, with Dim / Default / Bright presets.

The optional enhanced water (Water Quality, refraction, caustics, High reflections, lava glow) is its own module, documented in WATER.md.

Where the code lives

• Shaders: crates/benilla-assets/src/shaders/shadow_hook.wgsl (shared shadow sampling), fog_hook.wgsl (MONKEY p0: the ONE distance-fog law — fog_linear, fog_sample, apply_fog; terrain, wow_model, static_gx, liquid, enhanced_water, wow_effect and wdl all call it; classic is bit-identical to the old per-shader copies, and MonkeyFrame.fog_model = 1 is the FOG lane's extension point), monkey_frame.wgsl (the MonkeyFrame struct), crates/benilla-world/src/shaders/torch_depth.wgsl, and the lighting lanes inside static_gx.wgsl, wow_model.wgsl and terrain.wgsl. The three receivers mirror each other; the comments say where.
• World (crates/benilla-world/src): lighting/global_light.rs (light table packer, lanes, room claims, gains), lighting/daylight.rs, lighting/flicker.rs, static_gx/torch_depth.rs (cube-map cache), static_gx/shadow.rs, and the light spawning in terrain_stream/spawn/.
• Data rules (crates/benilla-formats/src): fire_light.rs (which models emit light, their colour and reach, the spell school rules) and room_claim.rs (which rooms a light may light).
• App (crates/benilla-app/src): torch_shadow.rs (caster selection), shadow_core.rs, character_shadow.rs, world_shadow.rs, blob_shadow.rs, entities/carried_light.rs, entities/spell_fx/lifecycle.rs, dynamic_interior.rs, debug_panel/lighting_controls.rs, and the cvars in cvars.rs / video.rs.
• Tools: benilla-extract <Data> wmolights <wmo> [--verts <group>], wmolamps, m2firescan print the inputs the system works from (groups, batch classes, portals, claims, flame emitters).

Invariants worth knowing before editing

• The shared light buffer's per-frame blob is 8784 bytes and the torch table 6416 bytes; both are mirrored in the shaders and pinned by tests. The blob is 21 header rows (336 B), the 256-slot point-light table (8192 B), then the MONKEY MonkeyFrame block (16 rows, 256 B; nothing before it moves). Every WowLight mirror (terrain, wow_model, static_gx, liquid, enhanced_water, wow_effect, wdl) declares it as monkey: monkey_frame::MonkeyFrame after points:

  row	x	y	z	w
  fog0	height_fog_density	height_fog_height	height_fog_falloff	curve_blend
  fog1	sun_fog r	g	b	sun_fog_strength
  fog2	end_fog r	g	b	end_fog_distance
  fog3	fog_model (0 classic, 1 modern)	sun_fog_angle	0	0
  wind0	dir_x	dir_y	speed	gust
  wind1	time_s	sway_strength	grass_strength	tree_strength
  wet0	rain_rate	wetness	ripple_time_s	snow
  misc	bender_count	time_of_day 0..1	night 0..1	0
  benders[8]	world x	world y	world z	radius

  Positions are Bevy world space (Y up, yards; WoW (x, y, z) = Bevy (-y, z, -x)), the wind direction is a unit vector in world XZ. Lanes write the MonkeyFrame resource (benilla-world/src/lighting/monkey_frame.rs); global_light::pack_monkey_frame packs it after the point table and fills time_of_day / night itself. All zero = no visual change.

• World lights use upstream's WorldPointLight, never Bevy's PointLight.

• WGSL only fails at pipeline creation, so a shader edit is verified by running a world scene, not by cargo check.

• Exterior point lights are selected per draw unit (12 slots, ranked against the chunk's box); the cube-map occlusion is evaluated for the nearest three.

Build

cargo build --release -p benilla

Debug tracing: WOW_TORCH_TRACE=1, WOW_POINTS_DUMP=1, WOW_SHADOW_TRACE=1, and the cvar interiorDebug 1..4.

Licence

Same as upstream: MIT OR Apache-2.0. Code and techniques taken from other projects (WarcraftXL, by iThorgrim) are credited file by file in THIRD-PARTY.md.