Overdrive cables: raised cross-section, shadows, and deferred lighting

[Anarchid]

What

Gives the overdrive grid cables a real presence in the 3D world, in three layered changes:

1. Raised "tent" cross-section — the flat, ground-hugging ribbon becomes a raised tube.
2. Shadow casting — the cables drop shadows in the engine's shadow-map pass.
3. Deferred lighting — the cables participate in deferred lighting (projectile lights) and the outline pass, via the model gbuffer.

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1. Tent cross-section

Why

Once the cables read as 3D tubes rather than painted stripes, the flat ribbon's lack of volume became obvious — especially where a cable crosses a cliff at an oblique angle. There the cross-sections only translated vertically (no rotation), so the cable looked like a "serpentine ladder" poking out of the terrain with no thickness.

How

• emitMainRibbon → emitTentHalf(side, …): emits one slope as a single triangle strip, ridge (cableUV.y = 0) → outer ground edge (cableUV.y = ±1).
• The two slopes are dispatched to separate GS invocations (0 = left, 1 = right). This is what makes the full raised cross-section fit: each slope keeps its own GL_MAX_GEOMETRY_OUTPUT_COMPONENTS budget (~50 verts), whereas one combined sheet (~100 verts) would bust the 1024 min-spec ceiling.
• The ridge is lifted along the local terrain normal, so on slopes/cliffs the tube banks into the surface (the terrain supplies a cross frame that stays ~perpendicular to the cable tangent) instead of displacing flat.
• No fragment-shader change. cableUV.y = 0 was already lit as the cylinder top and ±1 as the sides, so the real raised geometry now agrees with the previously-faked cylinder normal instead of fighting a flat strip.
• New constant TENT_HEIGHT_FACTOR controls ridge lift (0.0 reproduces the old flat ribbon).
• Twigs moved to invocations 2–4 (capped at 3; invocation 1 was reassigned to the second slope).

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2. Shadows (cast + receive)

Casting and receiving are unrelated mechanisms; both are wired up.

Casting re-draws the live cable VAO through a SHADOW_PASS shader variant from gadget:DrawShadowUnitsLua — the same callin cus_gl4 uses to shadow units, so cables drop into the same shadow map.

• Identical tent geometry, but vertices go through the Recoil shadow-map transform (shadowView * world; xy += 0.5; shadowProj * — mirroring cus_gl4.vert.glsl; using the precombined shadowViewProj omits the +0.5 recenter and pushes geometry out of the shadow frustum).
• The FS writes depth only and reuses the forward grow/wither discards, so a growing/withering cable casts a shadow trimmed to exactly its visible extent.
• No information leak: own/spectator cables always cast; enemy cables cast only where they're in LOS (the same $info:los gate the visible cable uses); ghosts never cast.

Receiving samples the shadow map in the forward FS — the cable's sun term was a bare dot(cylNormal, sunDir) with an ambient floor and never tested the map, so it stayed at full sun under any occluder.

• Uses the engine receive convention (shadowView * world; xy += 0.5; textureProj against a sampler2DShadow, as in map_lava.lua).
• The coefficient darkens only the sun term — a shadowed cable falls to DIFFUSE_FLOOR (ambient), not black — and the specular. Bubbles are composited afterwards and stay emissive, matching the existing LOS-dim design (plasma reads as lights in the dark).
• Gated on Spring.HaveShadows(): with shadows off, getShadowCoeff returns 1.0 without sampling and $shadow isn't bound.

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3. Deferred lighting

Draws the live cable into the model gbuffer (cus_gl4's RENDERING_MODE==1 MRT) from a DEFERRED_PASS variant, run on gadget:DrawOpaqueUnitsLua's deferred invocation.

• The FS writes the cable's cylinder normal + a capacity-tinted diffuse (plus depth, via the draw) into normtex/difftex instead of a lit colour. Deferred projectile lights then shade the cable's own surface rather than letting the terrain underneath bleed through it (which also explains a long-standing "terrain normals affect the cables" artefact — the light pass was reading the terrain gbuffer at the cable's pixels).
• Bonus: the outline pass reads the same gbuffer, so it stops cutting through the cable geometry.
• The forward DrawWorldPreUnit draw is unchanged — the visible cable, its lighting, and the animated bubble/pulse glow all stay forward-only, so the light pass can neither dim nor re-light the glow. The gbuffer is purely auxiliary geometry for screen-space effects, exactly as it is for units (which also draw both forward and deferred) — so there's no double-lighting.
• The GS reuses the normal cameraViewProj path and skips the coverage-SSBO update in the deferred pass (the forward pass owns coverage; the deferred draw binds nothing at binding 6, and a second per-frame update could double-clear ghost bits). Ghosts and enemy-out-of-LOS cables are gated out of the gbuffer with the same rule the shadow pass uses.

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Testing

/luarules reload, then:

• Tent: inspect cables crossing terrain steps obliquely; set TENT_HEIGHT_FACTOR = 0.0 to A/B against the old flat ribbon.
• Shadows: confirm cables cast into the shadow map and the shadow tracks growing/withering; scroll to check there's no shadow offset.
• Deferred: pass a projectile light (Newton stream, firing unit, explosion) over a cable in shadow/at dusk — the light should rake the tube's near face with the rounded cylinder falloff, not a flat terrain-shaped wash.

Known follow-ups (deferred)

• Left/right edge displacement doesn't yet respect the 2D downhill direction of the terrain (the B3 sign is chosen only to match perpAB).
• Sheer cliffs are still under-segmented (boundaries are uniform in 2D t), so very vertical faces get few rings to drape over.
• The bubble/pulse glow is not yet routed to the gbuffer emission target, so it doesn't feed bloom — a separate, optional nicety.

🤖 Generated with Claude Code

[Anarchid]

[Anarchid]

Added a second commit (99a0b5991) on top of the tent geometry: the cables now cast shadows, which does a lot to seat them in the world rather than reading as a flat overlay.

How it works:

• Compiles a SHADOW_PASS variant of the same VS/GS/FS and draws it from gadget:DrawShadowUnitsLua (the same engine callin cus_gl4 uses to shadow units).
• The GS reuses the tent geometry but transforms with Recoil's shadow-map convention from cus_gl4.vert.glsl — shadowView, +0.5 XY recenter, then shadowProj (the precombined shadowViewProj omits the recenter and casts offset/no shadow). Coverage SSBO bookkeeping is skipped in the shadow pass.
• Compile-failure-safe and fully separable from the tent commit if you'd rather take just the geometry.

A deferred-lighting pass (projectile lights on the cables via the model gbuffer / DrawOpaqueUnitsLua) is the obvious next step but is not in this PR.

🤖 Generated with Claude Code

[Anarchid]

[Anarchid]

Former: example of the outline shader cutting into the cable
Latter: example of how adding the deferred write solves the problem