Birth
Make new particles: a stream every frame, a burst all at once, one on each vertex or piece of a mesh, or a liquid filling one.
Make new particles: some every frame, all at once, one on each vertex of an object's mesh (for cloth and ropes: bind them with Bind, Mesh Edges), one on each piece of it (to smash: glue them with Bind, Pieces), or the event's Liquid filling it.
- Add it
- EventAdd OperatorBirthBirth
- Sends on
- Nothing: it has no wire.
- Influence
- No: a value can’t weigh it.
When to use it
Every flow needs at least one Birth: it's where particles come from. Pick its Mode by what you're making:
| Mode | For |
|---|---|
| Every Frame | A stream: sparks, dust, rain, a fountain, smoke and fire |
| All at Once | A burst: an explosion, a pop of confetti, a handful of rocks |
| On Vertices | Cloth and ropes, with Bind Mesh Edges; or particles that start as a mesh's shape |
| On Pieces | Something to break, with Rigid Body and Bind Pieces |
| Fill | A liquid filling a closed mesh, or pouring in from one, with Liquid |
| In the Gas | Sparks and embers thrown off where the flow's fire burns |
Where they're born
- Every Frame and All at Once make particles at the world's origin. Put a Position below the Birth to place them: in an object's box, on its surface, inside it or along a curve.
- On Vertices and On Pieces make them where the object's vertices, or its pieces, are on the Start frame.
- Fill makes the event's liquid inside the object's mesh, which should be closed.
- In the Gas makes them where the flow's fire burns, as the last frame left it.
Set it up
In the flow editor, select an event (or add one: ShiftA ▸ Event) and add Add OperatorBirthBirth.
Pick the Mode, and set how many: Per Frame for a stream, Count for a burst.
For a stream or a burst, add Add OperatorBirthPosition below it and name the emitter in its Object. Add a Speed to send them off.
Settings
As the flow editor’s sidebar shows them. Changing any of them marks the bake old; those marked Keyframable can also change through a bake.
How new particles are made.
- Every Frame: Some new particles every frame.
- All at Once: All of them on one frame.
- On Vertices: One on each vertex of an object's mesh, all on one frame.
- On Pieces: One on each piece of an object's mesh (its loose parts, as Fracture cuts them), all on one frame. With a Rigid Body each is its own piece's shape; glue them with Bind, Pieces.
- Soft Body: A lattice of particles filling an object's mesh (closed), all on one frame, held together as one soft body by a Soft Body operator; the mesh rides on them, bending and squashing as they do.
- Fill: The event's Liquid filling an object's mesh (closed), on one frame; or, with Stop, kept full until then: an inflow, its liquid going at Velocity while inside.
- In the Gas: Some every frame where the flow's fire burns (a Smoke Source makes it), more where it burns brighter, going with the gas: sparks and embers.
The object this operator works with.
Shown when Mode is On Vertices, On Pieces, Soft Body or Fill.
How far apart the soft body's particles are: smaller follows the mesh closer and bends finer, but is slower.
Shown when Mode is Soft Body.
New particles made every frame.
Shown when Mode is Every Frame or In the Gas.
How many in all, or for spawn, how many from each particle as it arrives.
Shown when Mode is All at Once.
How fast the liquid filling the object goes as it starts, or for an inflow, while inside it.
Shown when Mode is Fill.
Born only where the gas goes faster than this, in metres a second: where it rushes, not where it smoulders. 0 anywhere it burns.
Shown when Mode is In the Gas.
Per Frame and Count
Per Frame is spread evenly through each frame, so a stream is smooth however fast it goes, and a frame always has its full share. Keyframe it to ramp a stream up and down: the bake makes as many as the curve's area.
Count is how many in all, born on the Start frame.
With Draft on, a Birth in an event with a Liquid makes an eighth as many, so the coarser liquid fills as much.
Start, Stop and End
Start is the first frame with births. Turn Stop on to end them after End, the last frame with births. Without Stop, a stream goes on to the end of the bake.
Fill and inflows
Fill makes the event's Liquid inside the Object's mesh on the Start frame: a column of water to fall, a glass to fill. The mesh should be closed. Turn off its rendering, as the Liquid starters do, or it shows in renders.
With Stop on, it's an inflow instead: the mesh is kept full of liquid from Start to End, and the liquid inside it goes at Velocity: a tap, a hose, a wave pouring in.
On Vertices and On Pieces
On Vertices makes one particle on each vertex of the Object's mesh, with its modifiers, all on the Start frame. Bind Mesh Edges then holds them together along the mesh's edges, as cloth or a rope, and Group Test can send some on by a vertex group (to Pin a cloth's corners).
On Pieces makes one particle on each loose part of the mesh, as Fracture cuts them. With a Rigid Body, each one is its own piece's shape; glue them with Bind Pieces to make something that breaks.
In the Gas
In the Gas makes Per Frame particles in the flow's gas, which a Smoke Source in this event or another gives off. They're born where the flame is brighter than Flame Above, more where it burns brighter, and only where the gas goes faster than Speed Above (metres a second), so sparks fly from where the fire rushes rather than where it smoulders. Each starts with Inherit of the gas's velocity there. While nothing burns that brightly, none are born.
Give them a Smoke Force to ride the gas after, and a Delete so they die out. It reads VecFlow's own gas: with NVIDIA Flow none are born.
Works with
- Position places a stream or a burst.
- Speed sets them going.
- A Birth can be in any event, and an event can have more than one: two streams at once, or a burst and a stream.
Problems you may see
Nothing is born: add a Birth operator to an event
A flow needs at least one Birth to make particles.
event: operator ends before it starts
Its end frame is before its start frame.
event: operator fills with the event's liquid: add a Liquid
event: operator: 'object' has no mesh to fill
event: operator: 'object' has no vertices
event: operator: a soft body is held by a Soft Body operator in this event: add one
Errors stop a bake; warnings don’t. Every message is on the Messages page.
Related
- The Particles starter, and the Emission panel it uses without a flow
- Liquids, Cloth, ropes and soft bodies, Destruction