In this lesson, you will learn how to orchestrate the physical lifecycle of particles by mastering the interplay between birth duration, initial momentum, and drag within the VFX Graph.
Controlling the Simulation Context
When you spawn a particle, its "existence" is defined by two primary factors: how long it remains active and how it interacts with the physics of your simulation space. In the VFX Graph, this is governed by the Initialize and Update blocks.
Setting Lifetime
The Lifetime node in the Initialize context acts as a countdown clock for each individual particle. By setting a Random range (e.g., between 1 and 3 seconds), you introduce natural variance into your effect, preventing the visual "pop" that occurs when all particles expire simultaneously. Once the lifetime reaches zero, the particle is culled by the simulation.
Defining Velocity and Drag
Velocity is the directional force applied at birth, while Drag acts as a resistance factor over time. To simulate realistic motion, you generally define the Velocity in the Initialize context to set the starting vector. However, to give your particles weight—making them feel like smoke, embers, or debris—you must apply Linear Drag in the Update context.
Think of it this way: Velocity is the initial "kick" the particle receives, while Drag is the atmospheric friction it fights against. Without drag, a particle maintains its initial velocity indefinitely (or until it hits a wall). By adding a drag value, you force the particle to gradually decelerate, creating a more organic, weighted movement.
// Conceptual breakdown of the graph logic:
// 1. Initialize Block: Set Lifetime [Random: 0.5, 2.0]
// 2. Initialize Block: Set Velocity [Random Direction * Speed]
// 3. Update Block: Apply Linear Drag [Value: 1.5] to simulate air resistance
If you notice your particles are flying off into infinity too aggressively, don’t just lower the initial speed—increase the Drag in the Update context. This allows you to keep a high initial impact while ensuring the effect settles gracefully before the particles vanish at the end of their lifetime.
Key Takeaway: Particle lifetime defines the duration of the cycle, while the balance between initial velocity and continuous drag determines the physical weight and final trajectory of your effect.