#decal

The practical patterns for Sandbox.Decal: orienting the projection box to a hit normal, keeping a decal byte-identical across multiplayer peers, making paint follow an animated character, and scaling to thousands of decals without a performance cliff, plus the pitfalls that catch each one.

A projected Sandbox.Decal seated on a character's analytic hit surface (e.g. a capsule hit position) with a shallow projection Depth paints the base skin mesh but ends before the clothing renderers' outer shell, so paint shows only where bare skin peeks out. Increase Depth to span the cloth shell without punching through thin limbs.

A projected Sandbox.Decal renders its colour as lit surface albedo, not an unlit overlay: a pale/pastel tint washes out to a barely-there stain on a bright surface.

Lifting a flat overlay clear of the ground is only half the rule. Overlays also z-fight each other, and a full-lap overlay on a self-crossing path z-fights itself, which no single lift value can fix.

A world-space Sandbox.Decal is fixed in world space, so a splat spawned on a character projects onto empty air the instant they move. Parent the decal under the character, store the hit in a bone's local frame, and re-pin its world transform to that bone every frame so it re-projects onto the moving skinned mesh.

A Sandbox.Decal projects onto runtime-built chunk meshes (ModelRenderers) and conforms to stepped/curved faces, confirmed live on voxel terrain.

Sandbox.Decal self-seeds with Random.Shared.Int(10000) on enable: a decal spawned identically on two peers renders differently by default.

Sandbox.Decal instances are lightweight scene objects with no hard engine cap, so a persistent-paint system can hold thousands. The failure mode is a gradual frame-time sag driven by fill-rate/overdraw, never a crash cliff. Bound it with a convar-backed ring buffer and bench for your target hardware.