Blood Visual (Stains, World Feedback, HUD)

Canonical GDD content

Visual blood only. It does not change combat, survival, stealth, or other gameplay in this spec. Any future gameplay use of blood is [TBD].

Related: 03-Combat-System.md, 06-Inventory-and-Items.md, 08-Character-Creation.md, 09-Weapon-Customization.md, 11-Wetness-and-Rain.md, ../03-Enemies/01-Zombie-Design.md, ../03-Enemies/02-Boss-Zombies.md, ../06-Art-Audio/01-Art-Direction-and-MetaHuman.md.

Dirt / fouling is cancelled (no dirt meter, no workbench cleaning, no jam/spread-from-dirt). Use still reduces durability. See 09-Weapon-Customization.md.

Layers — [CONFIRMED]

Both exist (they are not alternatives):

Blood color is one palette for all living targets (player, zombie, boss, animal). Do not author separate human vs zombie blood colors unless that decision is reopened.

Mesh stain — material contract — [CONFIRMED]

• Approach: mask on the existing material, not a Material Layer Blend stack.
• Control: a single scalar BloodAmount in 0–1 per stained object (one value for the whole item/mesh, including multi-slot materials).
• Mask: authored per mesh. Shared/procedural masks are not the v1 contract.
• MID applies that scalar to the mask. Exact parameter names are [TBD] (technical art).
• If a mesh has no blood mask (or materials do not expose the stain path), it shows no blood. Missing mask is not a ship blocker for that asset, but the pipeline applies to all future content in this system.
• New melee / clothing / body content is expected to follow this pipeline; unmasked pieces simply stay clean-looking.

What can stain (attacker) — [CONFIRMED]

Stains the thing that scored a melee hit, when that hit connects and deals damage to a living target.

Counts:

• Any equipped item that can perform a melee hit (melee weapons, tools, building hammer, etc.).
• A firearm used as a melee strike (butt / bayonet / similar) — the gun mesh stains.
• Unarmed punch: skin of the hands if no gloves are worn; gloves only (not hand skin) if gloves are worn.
• Kick: shoes.

Does not count:

• Thrown melee / thrown items.
• Hits on structures, walls, doors, or other non-living props (nothing to bleed).
• Block / parry — the attacker's weapon does not stain from being blocked.

Ranged gunfire does not stain the firearm. It can still stain the victim (see below).

What can stain (victim and bystanders-on-body) — [CONFIRMED]

When a living target takes damaging hits (melee, firearms, explosives, or any other damage that actually deals damage):

• Their outer worn clothing can stain. Which slot is “outer” is [TBD] until clothing layers are designed; do not implement a layer-priority table yet.
• Items in inventory that are not worn do not stain.
• Hair and skin stain. That BloodAmount lives on the character/pawn, not on an item. Changing clothes does not clear body/hair blood.
• Eyes do not receive a mesh stain.
• Zombies and bosses use the same mesh-stain contract on their bodies (per-mesh mask + BloodAmount).
• Animals use the same living-target rules.

Dual state: item vs character — [CONFIRMED]

Both can be stained at once (e.g. bloody shirt item + bloody skin/hair on the pawn).

Accumulation — [CONFIRMED] rules, numbers [TBD]

• Amount added scales with damage dealt (attacker gear) or damage taken (victim clothes/body). Do not invent a formula, coefficient, or curve in code or docs.
• There is a ceiling (visual saturates; treat the scalar cap as 1.0 unless a different cap is decided later).
• Stains ease in (not a binary first-hit full coat).
• Stains do not decay until a wash system exists.

Wash — [CONFIRMED] intent, not this slice

Workbench cleaning of dirt/blood is cut.

Future wash sources (not built in the visual-pipeline slice):

• Faucet
• Water source
• Rain (wetness from rain is specified in 11-Wetness-and-Rain.md; washing blood with rain is still not decided)

Until a wash system exists, BloodAmount stays. Wash interaction, whether rain reduces blood, and whether wash is channeled are [TBD]. WetAmount is independent and must not clear blood by existing.

Networking, inspect, save — [CONFIRMED]

• Other players must see mesh stains (weapons, worn clothes, hair/skin, zombies/bosses).
• Mesh BloodAmount on items is instance state: world drops, loot, and workbench 3D inspect show the stain.
• Item and player character body/hair blood persist in the save record.
• Whether AI blood (zombie/boss/animal) is written into world persistence or only lives on the actor until despawn is [TBD].

HUD overlay is local-only and is not replicated.

Local HUD overlay — [CONFIRMED] existence, tuning [TBD]

• Blood marks on the local player's screen, then fade over time.
• Replaces staining the eye mesh.
• Duration, intensity vs damage, and exactly which events spawn it (incoming damage, camera-facing splatter, melee swing, combinations) are [TBD]. Do not copy a third-party vignette curve.

Gameplay — [TBD]

No stealth, infection, hygiene, or stat effect is specified. Do not hook BloodAmount into GAS or AI senses until a later decision.

Pipeline ownership — [CONFIRMED]

• Spec first; mesh masks and material wiring follow the contract above.
• This is a game-wide pipeline, not a one-weapon prototype. Content without a mask simply does not show the stain.

Open questions still [TBD]

Do not implement as if decided:

• Clothing outer-layer resolution.
• BloodAmount gain formula and easing.
• MID parameter names.
• HUD overlay triggers, duration, and intensity.
• Wash / rain / faucet implementation.
• AI blood persistence across server restart.
• World splatter/decal art direction (materials, lifetime, pooling) beyond “this layer exists.”
• Gameplay consequences of being bloody.