How surfaces work¶

Every impact asks the same question: what did I just hit? The answer is a surface, one label carried by the mesh you shot or by the floor you stepped on. Bullet effects, decals and footstep sounds all read that one label, so setting it once on a mesh makes all three correct at the same time.

This page tells you where the label lives, who reads it, and what it picks.

The surfaces that ship¶

Six surface types are declared in the project, in the SurfaceType1 to SurfaceType6 slots, plus the engine Default. Each one has a Physical Material in Content/TheLastTemplate/Materials/PhysicsMaterials/.

Surface	Physical Material	Note
`Default`	`PM_Default`	what you get when nothing sets a surface
`Metal`	`PM_Metal`	used by `MI_Prop_Metal` and `MI_Prop_SteelPainted`
`Wood`	`PM_Wood`	used by `MI_Prop_Wood`
`Grass`	`PM_Grass`
`Blood`	`PM_Blood`	used by `M_CharacterColor`
`Glass`	`PM_Glass`
`Water`	`PM_Water`

L_ShowcaseMap has a wall of six panels, one per surface, so you can fire at each of them and compare.

Where the label goes¶

Two fields can carry a physical material, and they do not behave the same.

On a material or a material instance: the Phys Material field.
On a placed mesh component: the Phys Material Override field, under Collision.

A physical material on a material is invisible to a simple trace

A physical material set on a material is only read when the trace runs against per polygon collision. Simple collision, which is what a mesh uses by default, never sees it, and gunfire traces against collision. So a mesh whose surface only lives on its material still gives you the default impact. Put the PM_* on the mesh component's Phys Material Override when you want bullets to react. The six panels in L_ShowcaseMap are set up that way, not through their materials.

What reads a surface¶

Two assets, and only two.

Asset	When it looks	What it picks
`BP_WeaponManager`	a bullet lands	impact effect, decal, impact sound
`AN_FootstepSound`	a foot lands	footstep sound, and the noise the AI hears

Content/TheLastTemplate/Blueprints/ActorComponents/BP_WeaponManager
Content/TheLastTemplate/Animations/AnimNotifies/Character/AN_FootstepSound

Nothing else in the template reads the surface. Melee, explosions and throwables do not change with what you hit. A punch plays the sound in the Impact Sound field of BP_CombatComponent at the bone it connected with, whatever that bone is made of. See How melee works.

What a surface picks¶

Three sets of assets, one per stage.

Stage	Folder	What ships
Impact effect	`Content/TheLastTemplate/Niagara/Impacts/`	`NS_Impact_Blood`, `NS_Impact_Concrete`, `NS_Impact_Grass`, `NS_Impact_Metal`, `NS_Impact_Water`, `NS_Impact_Wood`
Decal	`Content/TheLastTemplate/Materials/Effects/Decals/Instances/`	`MI_Decal_Impact_Blood`, `MI_Decal_Impact_Concrete`, `MI_Decal_Impact_Dirt`, `MI_Decal_Impact_Glass`, `MI_Decal_Impact_Metal`, `MI_Decal_Impact_Wood`
Sound	`Content/TheLastTemplate/Audios/Footsteps/`	`SC_FS_Concrete`, `SC_FS_Grass`, `SC_FS_Ground`, `SC_FS_Metal`, `SC_FS_Water`, `SC_FS_Wood`

Read those three lists carefully, because they are not a clean grid and the names lie a little. NS_Impact_Concrete and MI_Decal_Impact_Dirt have no surface of the same name. Glass has a decal but no Niagara system of its own. AN_FootstepSound wires five of the six sound cues, leaving SC_FS_Grass out, while BP_WeaponManager wires a different five and leaves SC_FS_Ground out. The file names are not the wiring. The switch inside those two assets is, so open one and follow your surface through it before you assume anything.

Bullet impacts and footsteps share the same sound cues. Changing SC_FS_Metal changes both.

The six decal instances are all children of M_Decal_Impact and share two 4 by 4 atlas textures, T_Decal_Impact_MRA_4x4 and T_Decal_Impact_N_4x4. They differ mostly by Atlas Row, which picks the cell, and by Surface Tint, Opacity Mul and Rough Damaged. The six Niagara systems are built on four shared emitters, NE_Debris, NE_Dust, NE_Flash and NE_Spark, and expose User.ImpactStrength, User.DustTint, User.DebrisTint and User.FreshBreak.

Footsteps also make noise the AI hears¶

AN_FootstepSound does two jobs on the same beat. It plays the cue for the surface, and it reports a noise event to the AI perception system. The audible range is read from two fields on the notify, Walk Noise Range and Run Noise Range, and the current gait decides where between them the step lands. A sprinting player is heard from much further than a walking one.

What you place on an animation is never AN_FootstepSound itself. It is one of its two children, AN_FootstepSound_L and AN_FootstepSound_R, which do nothing but say which foot it was through their Set Left Foot Up field. All the work, and both range fields, live on the parent. Change them there and the player, the NPCs and the infected all follow, because they share the same animation sequences.

To place the notifies on your own animation, run the AM_FootstepSounds animation modifier on the sequence. It adds the left and right notifies for you. See Use your own animations.

For what the AI does with that noise, see [Noise and distractions](..

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