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Brush behaviours

Behavior, in Brush Studio ▸ General, decides which of six engines a preset paints with: Paint, Watercolor, Eraser, Smudge, Deform or Fill.

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Every brush preset is built on one of six behaviours. Most of Brush Studio (Size, Spacing, the nozzles, the dynamics) works the same way whichever one you pick, and the handful of settings that belong to a single behaviour appear in General underneath Anti-alias, as a small block that changes with the dropdown above it.

Paint

The default behaviour: dabs of the brush colour build up along the stroke. On its own it is fast and smooth, because the whole stroke composites in one pass, which is what lets Accumulation act as a true ceiling however many times you cross the same spot.

Switching on Pigment, Impasto or Mix, or picking a Blend Mode other than Normal, moves the brush onto the slower path that reads the canvas under every dab. That is what unlocks those effects, and it also means tone can build past the single-pass look where a stroke overlaps itself.

Its own rows are Impasto, Pigment, Pigment Strength and Mix.

Mix is the dirty brush: how much of the colour already under the tip the stroke picks up and carries along with it. Raise it and painting a light colour across a dark one drags some of the dark along instead of covering it cleanly, which is most of what makes traditional media read as traditional. It is the same parameter the Smudge behaviour uses below, where it does a different job. At 0 it is off and costs nothing.

Watercolor

The six shipped WC presets do NOT use this behaviour. They are Paint with Wet Edges, the General row that darkens the rim from the stroke's own coverage: cheap, and it cannot stall mid-stroke. Pick Watercolor here when you want the fluid solver itself.

A wet-media simulation: pigment spreads, thins and pools instead of stamping cleanly. Accumulation feeds how much pigment is loaded rather than capping a flat colour, and the wash keeps settling for a moment after you lift the pen.

Its own rows are Spread, Granulation and Rim Boost. Spread is how far the wet paint diffuses, and a higher spread also thins the wash so less pigment lands per dab; Granulation is how much pigment settles into the paper's texture as it dries; Rim Boost is the strength of the darker edge that forms where a wash pools.

Eraser

Paints with the same dab, spacing and dynamics model as Paint, but removes colour from the layer instead of depositing it. It has no rows of its own.

Smudge

Drags the colour already on the canvas along the stroke, the way a finger would smear wet paint, rather than adding new colour.

Its own rows are Smudge, how much of the colour under the tip is carried forward, and Mix, which opens the pick-up from a backward line into a ring so a high value disperses colour in a cloud instead of dragging it along the path. The nozzle, Size, Spacing, Hardness and the dynamics shape the smear exactly as they shape a painted stroke.

The Smudge tool on the toolbar runs this behaviour on whatever preset is active, so any brush in the library works as a finger and its tip and texture are what make one smear differ from another. That is also why nothing ships as a Smudge family any more: forcing the behaviour is what makes a brush a smudge, not a tag on it. The tool keeps its own preset slot, remembered between sessions.

Deform

Warps the pixels already on the canvas inside the tip's footprint, without adding or removing colour: a liquify tool built as a brush.

Its own rows are Type, which is Pinch, Push, Twirl or Bulb, and Strength. Push drags pixels along the stroke's direction; the other three distort around the tip's centre. Colour and Blend Mode play no part, since nothing new is being painted.

Fill

Skips dabs entirely: as you drag, Fill records the outline you draw, and on release it fills the area that outline encloses with the active colour, closer to the Fill tool than to a brush stroke.

Its own rows are Fill Pattern, which is Solid, Screentone, Hatch, Cross-hatch or Grunge, and Scale, from 0.25x to 4x. The five shipped Fill presets are one per pattern. Most of the nozzle and dynamics controls that matter to Paint have no effect here, since no dabs are stamped.