Liquid Simulation

Each frame the node encodes a complete fluid step in compute and render passes on the GPU, before any generator render pass:

1. Splat injection — emitters inject velocity (always) and dye (gated by Emit) as additive Gaussian splats of Radius.
2. Mask ingest — if an image is connected, its luminance becomes a sim-resolution mask; a normal-flow estimate (v ≈ -(∂m/∂t)·∇m / |∇m|²) converts mask motion into velocity, and the silhouette outline emits a soft dye band.
3. Advection — velocity and dye are advected through the velocity field, dissipating at Drag and Fade per second.
4. Vorticity confinement — curl is measured and re-injected at Swirl strength, restoring the small eddies numerical diffusion eats.
5. Projection — divergence, a pressure decay (Pressure), and Iterations Jacobi passes make the field incompressible, then the pressure gradient is subtracted.
6. Display — a fullscreen pass renders the chosen field into the node's texture, compositing the background underneath.

Emitter sources combine freely. The Points input takes any point structure (up to 1024 splats) — each point's velocity is derived from its frame-to-frame motion (index-matched, clamped at 20 units/s). When no cable is attached to Points, the X / Y ports act as a single emitter; a connected but empty cloud stays empty. Wander is strictly opt-in idle motion: near-stationary points (moving under 0.05 units/s) get a gentle golden-angle-decorrelated drift so a parked emitter still stirs the fluid — at 0 the simulation never animates by itself.

Mask Mode decides what a connected Image does:

Display picks what the output texture shows:

Quality sets the field resolutions (short viewport edge):

Changing Quality or the viewport aspect recreates all field textures and resets the simulation (a resize invalidates the field contents anyway). Reset clears everything on demand.

Background composites under the liquid inside the display pass: a solid color (alpha 0 = transparent, the default) or, when a Gradient node is cabled in, a multi-stop linear gradient at Gradient Angle degrees (clockwise-positive, per the Grafit rotation convention). Emitter color can animate: Hue Cycle rotates the hue in turns per second and Hue Spread spreads an extra hue offset across the points of a cloud.

The simulation covers the full viewport: Width and Height report the viewport fit size in Grafit units (origin at center, shorter edge mapping to [-1, 1]), so a Canvas node covers exactly the visible frame. Output is premultiplied alpha, and Enable = false clears the texture.

The velocity field also stays CPU-readable (shared-storage textures, snapshot refreshed at up to ~240 Hz with bilinear sampling), which is what lets a Liquid Flow node sample this simulation to push particles, points or any other geometry along the same currents.

Emitters

Mask

Solver

Display

Interactions worth knowing: Swirl fights Drag — high Swirl with low Drag gives long-lived turbulence, while high Drag flattens everything into slow drift. Fade governs how long dye persists independently of how long motion persists. Iterations mostly changes how "tight" and non-smearing the flow looks; Radius and Force together decide whether an emitter paints or blasts.

• Ink drop follows the mouse: Mouse position → X / Y, Radius 0.15, Emit on — classic ink-in-water trails
• Person stirs the liquid: a Vision segmentation mask → Image with Mask Mode Both and Mask Force 1.5 — the silhouette emits from its outline, blocks the flow, and pushes it as it moves
• Audio-reactive dye: Audio FFT → Remap → Force, and a beat signal → Emit, so the fluid only paints on hits; Hue Cycle 0.15 keeps the palette rolling
• Particles riding the current: Liquid Simulation → Liquid Flow → a particle or point system, so geometry moves along exactly the same field the visuals show
• Multi-point stirring: Geometry to Points (circle) → Point Animation (orbit) → Points, so a ring of emitters churns the frame; add Hue Spread 1.0 for a rainbow vortex
• Flow-field art: Display Velocity over a black Background gives a hue-mapped flow map that composites beautifully in Additive blend on a Canvas

• Like all generators, the output only reaches the screen through a Canvas node — and the simulation is viewport-sized, so a Canvas at Width/Height covers it exactly
• Quality is the main performance lever; High (384/1536) is significantly heavier than Medium. Iterations is the second lever
• Changing Quality or resizing the render window resets the fields — set up your output resolution before dialing in a look
• Nothing self-animates: with no motion on the emitters and Wander at 0, the fluid settles and stops. Wander is the deliberate opt-in for a "living" idle state
• A connected but empty Points cloud emits nothing — that is intentional, so a vision/particle source that momentarily has no points doesn't fall back to a stray center splat
• The background gradient only activates with a real Gradient cable; otherwise the solid Background color (transparent by default) is used
• Set Speed to 0 to freeze the field for a still frame without clearing it; use Reset when you want an actually empty tank