impact

What a round does where it lands. A flash goes off at the point of impact and a burst is thrown back along the surface normal — and what that burst is comes from the surface it hit, not from a colour parameter.

local hit = physics.raycast(muzzle.position, aim, 200)
if hit then
    effects.play("@builtin::systems.effects.combat.impact", {
        position = hit.point,
        params = { normal = hit.normal, surface = "metal" },
    })
end

normal takes exactly what a cast reports: every physics.raycast / raycastAll / raycastScreen / sphereCast hit carries { entityId, point, normal, distance, startedInside }, so the point goes to position and the normal goes to normal.

The surface it hit

surface is the parameter that makes this an impact rather than a burst. It is an enum, so it takes one of a closed list of names and a name outside that list raises and reports the ones that are in it.

Each row sets spark count, dust count, colour, speed, drag, gravity, particle size, how long the burst lasts and how bright the flash is. count, speed, spread and lifetime then scale the row the surface chose, so a big soft strike on dirt and a small hard strike on metal are the same asset.

Parameters

Cost

The size is what the effect's own backends report they hold at a representative instant — handle:stats().bytes — read identically on every engine, in every scene and on every repeat. The emitter vertex buffers an effect draws from come out of a pool shared across the process that grows in chunks, so a renderer.gpuMemory() delta taken around one play is that pool's growth as much as the effect's; what those buffers cost at the declared slot counts is below. The span is the median of five interleaved idle/loaded windows of the frame's measured GPU pass sum, which read 0.000 ms with a spread of about 0.008 ms: the effect costs less GPU time than that instrument resolves, and 0.01 is the bound the reading supports.

Measured on metal at the declared defaults: 31,524 bytes of emitter simulation state, plus 27,360 bytes of emitter vertex geometry — the spark emitter's 36 quantised slots at 760 bytes each. Slot counts are quantised in twelves so a spread of count values lands in a handful of pool buckets rather than one per value, and a surface that also throws dust leases a second emitter and spends its own slots on top.

What it draws with

The sparks and the dust are particles rather than geometry, so the only thing the shared material draws here is the flash itself.

See also

• @builtin::systems.effects.combat.tracer — the round that lands here.
• @builtin::systems.effects.combat.shockwaveRing — the front a larger blast pushes out from the same point.
• guides { path: "topics/physics" } — the casts that report a hit's normal.