Suminagashi Studio

A fluid simulation can keep changing the drawing after the brush lifts. Suminagashi gives that movement a defined stopping point.

The app runs its full fluid solver for a short settling period after each stroke, then clears the velocity and pressure while preserving the pigment. Wetness and Settle determine how long the movement continues; Taper controls how gradually it stops. These brush settings expose a deliberate compromise between fluid behavior and control over the finished drawing. With automatic flow off, moving the pointer over a settled painting leaves it undisturbed.

The pigment has its own model of color. A brush color is converted into absorption values, which describe how much light the ink removes from the paper beneath it. Where pigment accumulates, more light is absorbed. This gives overlapping strokes a denser appearance and lets the fluid carry mixtures of ink through the drawing.

Paper is handled in the final display pass. Fine grain, directional fibers, and broader mottling modulate the paper color underneath the pigment. They remain separate from the fluid's velocity and pressure, so changing the paper texture does not require running the painting through another simulation. A settled drawing can keep its contours while the surface beneath it changes.