Spawn

The Spawn section sets where each particle is made and how it is turned at that moment. Part, Attachment and Model emitters share it. Of those three, only Part emitters have the Use shape rows. Lightning, Rocks and Rope have a Spawn section of their own, described on their pages.

What it makes possible:

Flat cards that always face the camera. Orientation FacingCamera.
Streaks that follow a falling arc. Orientation VelocityParallel with an Acceleration.
A ring of particles from two rows. Rotation Y 0, 360, Position Z 3, Pos. Mode Local.
Eight particles at equal angles. Rotation Y 0, 360 with its Even dot on, Emit 8.
A sprinkler that sweeps one full turn a second. Rotation Y 0, 360 with its Even dot on, Rot. Cycle 12, Rate 12, Direction Front, Dir. Mode Local.
The shell of an explosion. Use shape on, Shape Sphere, Hollow 1.
Rain over an area. Shape Part set to a large invisible slab, with the emitter kept somewhere else.

The rows

The section starts collapsed. Expand it to see the rows.

Row	Kind	Starts at	Unit	What it does
Orientation	List	`None`		Turns each particle every frame, toward the camera or along its travel.
Pos. Mode	List	`Local`		Chooses the axes the Position offset is measured along.
Position	Two numbers for each of X, Y, Z	`0`	Studs	Moves the place each particle is made. Each axis picks a value between its two numbers.
Pos. Cycle	Two numbers	`0`	Particles	The length of one even sweep of Position. Shown while a Position Even dot is on.
Rot Order	List	`Global`		The order in which the three angles are combined.
Rotation	Two numbers for each of X, Y, Z	`0`	Degrees	Turns each particle as it is made. Each axis picks a value between its two numbers.
Rot. Cycle	Two numbers	`0`	Particles	The length of one even sweep of Rotation. Shown while a Rotation Even dot is on.
Z-Offset	Number	`0`	Studs	Moves each particle toward the camera.
Use shape	Switch	Off		Part only. Makes particles at random points inside a shape. Shows the five rows below.
Shape	List	`Box`		Part only. The shape: `Box`, `Sphere`, `Cylinder` or `Disc`.
Direction	List	`Outward`		Part only. Whether particles leave the shape outward, inward, or both.
Hollow	Number	`0`	0 to 1	Part only. Keeps particles out of the middle of the shape.
Look at initially	Switch	Off		Part only. Turns each particle to line up with the direction from the centre of the shape.
Shape Part	Instance, picked with `*`	The emitter itself		Part only. Another part to take the shape from.

Typing a value

Row	Takes	Notes
Z-Offset, Hollow	One number
Pos. Cycle, Rot. Cycle	Two numbers, or one number for both	Two numbers typed with the larger first are put in order.
Position, Rotation	Two numbers, or one number for both	The value is written to every lit axis.

Text that is not a number flashes red, and the old value returns.

On the Position and Rotation rows, the X, Y and Z buttons choose which axes the box edits. They do not switch an axis on or off. Click one or more to light them, then enter the value.

The box shows the value when the lit axes agree. It reads ~ when they differ.
With no button lit the box is empty, and typing does nothing.
Which buttons are lit is not saved.

With X and Z lit on the Position row of an upright emitter, -2, 2 scatters particles across the ground. Their height is not changed.

The order of events

Each particle is made in this order:

It starts with the position and rotation of the emitter, or of the linked object if a link is set.
On a Part emitter with Use shape on, it is moved to a random point in the shape.
Its Rotation is picked and applied, combined by Rot Order.
Its Position is picked and applied, according to Pos. Mode.
With Dir. Mode Global, the rotation of the emitter and of the link is dropped. Only the picked Rotation is kept.
Its launch direction is chosen, and SpreadAngle is applied to it.

Position is applied after Rotation. In Pos. Mode Local the offset therefore runs along the particle’s own turned axes.

The launch direction is set in the Motion section.

Orientation

Orientation turns each particle every frame. Exercise 5 uses it for the first time.

Option	What it does
`None`	No turning.
`FacingCamera`	Points the particle’s front face straight at the camera.
`FacingCameraWorldUp`	Turns the particle toward the camera, left and right only. It never tilts up or down toward the camera.
`VelocityParallel`	Points the particle’s front along its direction of travel. Its broad side stays turned toward the camera.
`VelocityPerpendicular`	Points the particle’s up axis along its direction of travel. Its front stays level.

The particle’s own rotation is applied on top of the Orientation. That rotation is made of the emitter’s rotation, the Rotation row and Rotation Speed. With all three at zero, FacingCamera points the front face exactly at the camera.

The two velocity options read the direction of travel from how the particle moved since the last frame. On the first frame they use the launch direction. On a frame where the particle has not moved, they do nothing.

Pos. Mode

Pos. Mode chooses the axes that the Position offset is measured along.

Option	The X, Y and Z of Position run along
`Local`	The particle’s own axes, after its Rotation has been picked. With Rotation at 0 these are the axes of the emitter, or of the linked object.
`Global`	The axes of the world.
`RigidLocal`	The emitter’s axes, before the Rotation is picked. If the emitter is linked, the linked object’s axes are used.

Take an emitter that is not rotated, with Rotation Y 0, 360 and Position Z 3.

Pos. Mode	Result
`Local`	Each particle sits 3 studs along its own turned Z axis. Together the particles form a ring of radius 3 studs.
`RigidLocal`	Every particle sits at the same point, 3 studs along the emitter’s Z axis.
`Global`	Every particle sits at the same point, 3 studs along the world’s Z axis.

All three options set the place once, when the particle is made. None of them makes a particle follow the emitter afterwards. Following is done by a link.

A Position of 0 on all three axes gives no offset. Negative numbers are accepted.

An emitter can be nested in a Model emitter that has Scale Motion on. The offset is then multiplied by the Model’s scale at that moment.

Position and Rotation

Each axis picks its own random value between its two numbers, once for each particle. Two equal numbers give exactly that value.

Rotation is measured in degrees. It is applied on top of the emitter’s rotation.

Rotation changes more than the look of a particle:

With Dir. Mode Local, the particle flies the way its picked Rotation points.
With Pos. Mode Local, the Position offset runs along the turned axes.

Rot Order

Rot Order decides how the three angles are combined. It applies to the Rotation row and to the Rotation Speed graphs in the Motion section.

Option	Order
`Global`	Y, then X, then Z
`LocalXYZ`	X, then Y, then Z
`LocalXZY`	X, then Z, then Y
`LocalYXZ`	Y, then X, then Z
`LocalYZX`	Y, then Z, then X
`LocalZXY`	Z, then X, then Y
`LocalZYX`	Z, then Y, then X

Global and LocalYXZ give the same result.
The order matters only when two or more axes are not 0.
The result is applied to the emitter’s rotation, not to the world’s axes. Dir. Mode Global is the exception, because it drops the emitter’s rotation.

With Dir. Mode Local, an order can leave one Rotation axis with no effect on the launch direction. If an axis does not fan the particles out, try another order.

Even dots

Each X, Y and Z button on the Position and Rotation rows has a small dot at its top-right corner. Click the dot to switch even spacing on or off for that axis. The dot is bright when on and dark when off.

With its dot on, an axis stops picking at random. It steps through its range in equal steps.

The Pos. Cycle row shows while any Position dot is on. The Rot. Cycle row shows while any Rotation dot is on. A Cycle is a count of particles.

A burst, with the Cycle at 0

The particles of one burst share the range out in equal steps.

Setting	Each particle gets
Rotation Y `0, 360`, Even on, Emit `8`	45, 90, 135 and so on up to 360 degrees. A complete ring.
Position X `-4, 4`, Even on, Emit `4`	-2, 0, 2 and 4 studs.
Any range, Even on, Emit `1`	The middle of the range.

In a burst of two or more, the lowest value of the range is never used and the highest always is. On a full turn, 0 and 360 therefore do not land on the same place. A Position range is not centred: -4, 4 gives -2 to 4.

A stream, with the Cycle at 0

A stream, with a Cycle

With a Cycle set, each new particle carries on where the last one left off. A Cycle of 12 covers the range in 12 equal steps, then starts again. One sweep takes the Cycle divided by the Rate, in seconds.

Setting	Result
Rotation Y `0, 360`, Even on, Rot. Cycle `12`, Rate `12`	360, 30, 60 and so on up to 330 degrees, then again. One full turn a second, in steps of 30 degrees.
The same, with Rate `24`	Two full turns a second.
Rot. Cycle `-12`	The same steps in the opposite direction.
Rot. Cycle `6, 12`	Each sweep picks its own length between 6 and 12 particles, as a whole number.

Bursts, with a Cycle

With a Cycle set, each burst is shifted a little from the one before. Later bursts fill the gaps the first one left.

Take Emit 8 over 0, 360 with Rot. Cycle 4. Each burst is turned 11.25 degrees from the last. After 4 bursts, 32 directions have been used.

Rules for Even axes

Position and Rotation step separately.
All Even axes of one row step together. Two Even axes therefore trace a diagonal line, not a grid.
The sweep carries on from one burst to the next. It starts again when the emitter is stopped.
An axis linked to another takes the other’s value. Its own Even dot is not used.
In Animate mode, Even axes pick at random.

Axis linking

The * button in the label of an axis row opens a small box. Its title is Link and the name of the row. The box links axes so that they always match.

To	Do this
Link an axis to the primary	Click the axis in the box. A linked axis reads `Y ->`.
Unlink an axis	Click it again.
Make another axis the primary	Hold Shift and click it. The primary reads `X *`.
Keep the result	Press Set.
Leave without a change	Press Cancel.

On Position and Rotation, a linked axis gets the same picked number as the primary, for every particle. Link Position Z to X and the particles scatter along a diagonal line.

On a graph row, a linked axis uses the primary’s graph and the primary’s random spread. Its own graph is not used while it is linked.

The same button is on five rows:

Row	Section	Kind
Position, Rotation	Spawn	Two numbers
Displacement, Rotation Speed	Motion	Graph
Size	Appearance, on a Part emitter	Graph

With several emitters selected, only the axes changed in the box are written.

Z-Offset

Every frame, Z-Offset moves the particle along the straight line between the particle and the camera. A positive number moves it closer to the camera. A negative number moves it farther away.

The move is real: the particle changes place. It is worked out afresh each frame and does not add up.

A Z-Offset of 2 on a particle 20 studs from the camera puts it 18 studs away. It also looks about 11 percent larger.

Uses:

A glow card pushed in front of the mesh it belongs to.
A picture lifted off a surface, so the two do not flicker where they overlap.

Use shape

Use shape is on Part emitters only. Switched on, it shows five more rows at the end of the section.

	Use shape off	Use shape on
Where a particle is made	At the emitter, or at the linked object	At a random point in the shape
Launch direction	Motion ▸ Direction	The direction from the centre of the shape through that point. Motion ▸ Direction is not used.

SpreadAngle, Position and Rotation still apply with Use shape on.

With Dir. Mode Local, the shape’s direction is used for the first step only. From the second step, the particle travels the way its own rotation points.

Shape

The shape takes its measurements from the Size of the shape part. The shape part is the emitter, or the Shape Part if one is set.

Shape	Where particles are made	Launch direction
`Box`	Anywhere inside the part’s Size.	From the centre toward the point. A point exactly at the centre goes along the part’s up axis.
`Sphere`	Inside a ball whose radius is half of Size X. Size Y and Z are not used.	Straight out from the centre.
`Cylinder`	Inside a cylinder whose radius is half of Size X. Its height is Size Y, along the part’s Y axis.	Straight out from the cylinder’s axis. A point on the top or bottom face goes straight up or down that axis.
`Disc`	On a flat circle whose radius is half of Size X. The circle lies across the part’s X and Z axes.	Straight out from the centre. A point exactly at the centre goes along the part’s up axis.

Direction

Option	What it does
`Outward`	Keeps the launch direction of the shape.
`Inward`	Reverses it. Particles fly toward the centre.
`InAndOut`	Reverses it for a random half of the particles.

Hollow

Hollow takes a number from 0 to 1. The hint in the empty box reads 0=solid, 1=hollow. A number outside that range is read as 0 or 1.

Particles are made between Hollow times the radius and the full radius. At 0.7 on a Sphere of radius 10 studs, they are made between 7 and 10 studs from the centre. At 1 they are made on the outer surface only, or on the rim of a Disc.

On a Cylinder, Hollow acts on the radius. The height is not changed.

Look at initially

Switched on, it turns each particle to line up with the direction from the centre of the shape. Switched off, particles keep the emitter’s rotation.

Shape Part

Shape Part names another part to take the shape from. It accepts a Part or a MeshPart, picked with the * button in the row’s label. The picking box has no Clear button.

With a Shape Part set:

The shape takes that part’s Size, position and rotation, and follows the part as it moves.
Particles are made at the Shape Part, not at the emitter.
Each particle’s own rotation still comes from the emitter.

The row starts as the emitter itself, which counts as no Shape Part. To go back to the emitter’s own shape, pick the emitter. If the Shape Part is removed, the emitter is used again.

The setting is kept in an ObjectValue named ShapePart inside the emitter. See EmitParent, Link, AccelTarget, ShapePart.

Limits

Of Part, Attachment and Model emitters, only Part emitters have Use shape and its five rows. Lightning has a form of its own.
A Sphere, a Cylinder and a Disc take their radius from Size X alone.
Pos. Mode sets a place once. It does not make particles follow the emitter.
An Even axis needs a burst or a Cycle. In a stream with the Cycle at 0 it gives the middle of the range.
With the camera exactly above or below a particle, FacingCameraWorldUp does nothing on that frame.
Z-Offset needs the player’s camera. Fired from a server Script, it acts on the server’s camera, and no player sees the result.