VfxTrailDefinitionData

Class Documentation

The settings of a trail ribbon, held by its mTrail.

The ribbon is built by walking its points from one end to the other, and mSmoothingMode picks the direction. The walk decides two things other properties depend on: where the texture's u = 0 lies, and which end mCutoff removes.

Properties

mBirthTilingSize

Embed<ValueVector3> = { "constantValue": [0, 0, 0], "dynamics": null }

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Texture tiling, evaluated once per particle when it spawns and kept for its life, so its dynamics can give each point a different value. Only x and y are used.

x is the length of one texture repeat along the ribbon, in world units: u = distance / x. 0 or a negative value makes u = 0 everywhere, so the whole ribbon samples one column of the texture.
y sets how much of the texture spans the ribbon's width, centered on v = 0.5:

`y`	`v` span across the ribbon
`0`	the full texture, `0` to `1`
positive	`halfWidth / y`, so the span follows the ribbon's width in world units
negative	the constant `-y`

mCutoff

F32 = 0

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Maximum length of the ribbon, in world units, measured along the ribbon from the point where the walk starts. Points past that length are not drawn. 0 or a negative value draws the whole ribbon, and the first point is never cut.

It truncates by total length. It does not break the ribbon where two particles are far apart. Modes 0 and 1 of mSmoothingMode cut the oldest end, mode 2 cuts the newest end.

mMaxAddedPerFrame

I32 = 0

Documentation Edit documentation

Maximum number of particles the emitter spawns in one update. Since every particle is a ribbon point, it caps how many points the ribbon gains per frame. 0 or a negative value sets no cap.

mMode

U8 = 0

Documentation Edit documentation

How the texture's u coordinate is assigned along the ribbon.

Value	Behavior
`0`	`u` is the distance along the current ribbon from the start of the walk, measured again every frame. The texture slides along the ribbon whenever a point is added at the head or removed at the tail.
non-zero	Wake mode. Each point keeps the `u` it was born with: the total distance the emitter's spawn point had travelled when that particle spawned. The texture stays pinned to the world path, and points appearing, dying or being cut off do not move it.

In both modes the distance is divided by mBirthTilingSize.x.

mSmoothingMode

U8 = 0

Documentation Edit documentation

Smoothing, and the direction the ribbon is walked in.

Value	Smoothing	Walk
`0`	none	newest to oldest (head to tail)
`1`	on	newest to oldest (head to tail)
`2`	on, and width limited on sharp turns	oldest to newest (tail to head)

Smoothing does two things, and neither adds points:

Each point's position is replaced by the average of the particles up to k places before and after it, where k (0 to 3) comes from a global engine setting rather than from the emitter.
At each joint the width direction is turned halfway between the directions of the two segments that meet there, so the ribbon keeps its width through a bend instead of kinking.

Mode 2 also narrows the ribbon after sharp turns. When a joint turns further than a threshold angle, the limit on the half-width drops by up to half the segment length, more for sharper turns. Each gentle joint after that raises the limit by half a segment length again, never beyond twice the authored half-width. Along the walk, no point is wider than the current limit. The threshold angle is not yet identified.

The walk direction is not cosmetic. It moves u = 0 to the other end of the ribbon and makes mCutoff remove the other end.

Referenced by 1 class · 1 property

VfxPrimitiveTrailBase mTrail Embed<VfxTrailDefinitionData>