Simulation
One physics world drives everything — particles, cloth, hair, soft and rigid bodies, even fluid and smoke — all from the same solver.
DNA simulates motion with a single, shared physics world. Instead of a separate engine per effect, every kind of simulation lives in the same world and is solved together. That means a cloth flag, a pile of rigid blocks, a hair groom, and a puff of smoke can all interact in one scene without you stitching different systems together.
One solver, many behaviours
Under the hood there is just one solver running on your GPU. What makes a piece of geometry behave like cloth versus a rigid body versus hair isn't a different engine — it's which rules (the forces and connections) are applied to it.
You pick a behaviour by choosing a node:
simulation.particle — points that fly, fall, or pile up (sparks, dust, sand, snow).
simulation.cloth — flags, banners, capes on a mesh.
simulation.hair — strands and grooms.
simulation.soft_body — squishy, jiggly meshes that hold their volume.
simulation.rigid_body — solid objects that collide and stack.
simulation.fluid and simulation.smoke — liquids and gas.
These all feed into a Physics World, the coordinator node that gathers your bodies, colliders, forces, and joints and runs the simulation. You can even wire raw geometry (say, a sop.scatter) straight into Physics World — with no other setup it's treated as a rigid body, so it "just works."
Because everything shares one world, different sim types collide with and push on each other for free. Drop rigid bodies onto a cloth sheet and they interact — no special bridge node required.
Simulations need PLAY to advance
A simulation moves forward in time only while playback is running. This is different from most nodes, which recompute instantly whenever you change something.
Play — time advances and the solver steps forward, frame by frame. This is the only way a sim builds up motion.
Pause — the simulation freezes exactly where it is. You can still inspect the frame, tweak nodes, and look around, but the bodies hold their pose and don't settle, fall, or drift.
So if your cloth is hanging stiff and nothing is moving, the first thing to check is whether you're actually playing.
Bursts and one-shot events still depend on playback to evolve. A pile won't keep settling and a fountain won't keep spraying while paused — pausing holds the whole world still.
Resetting a simulation
A sim builds its state up over time, so to start fresh you rewind. Scrubbing the timeline back to the start re-runs the simulation from the beginning, so frame 1 always looks the same way it did the first time. This makes it easy to dial in a look: change a parameter, jump back to the start, and watch it play out again.
Because the world re-simulates from the start when you scrub backwards, the result is repeatable — the same settings give you the same motion every time.
Scrubbing backwards into the middle of a sim re-runs everything from the start to get there, which can take a moment on heavy scenes. For long or expensive simulations, let it play forward rather than scrubbing around.
Forces, colliders, and constraints
A simulation gets interesting once things push and bump into each other:
Forces — gravity, wind, attractors, vortices, turbulence, and drag. See simulation.force_field and Forces & collisions.
Colliders — static shapes (and Distance Fields) that your sim can't pass through. A Volume wired in as a collider becomes a solid boundary.
Joints and constraints — pin bodies together, hinge them, or weld them. See Joints & constraints.
You can also ask questions about the world — raycasts, overlaps, triggers — with Queries (sim-free).