Fill
The bucket tool — its three boundary scopes, the gap and expand controls, fold filling across planes, and the replace rule.
Reference
- Tool
- Fill
- Panel
- Tool Options
- Section
- Fill
The Fill tool floods an enclosed region with a solid colour. Tap inside an outline and the region bounded by the surrounding ink is filled.
The flood is geometry-based, not colour-based. Boundaries are not sampled from the rendered pixels; each bounding stroke's centreline is rasterized as a solid thick line, so a textured, grainy or soft-edged brush still forms a watertight wall. A rough charcoal outline closes a region exactly as a hard inking line does.
There is no tolerance control
Because the boundary comes from stroke geometry rather than from colour similarity, a tolerance would have nothing to act on. The flood's threshold is a fixed internal constant and is not exposed anywhere in the interface. Region closure is controlled with Close gap, not with a tolerance.
Controls
The colour laid into the region. This is the shared brush colour, so it is the same swatch the QuickStrip and the paint tools use.
Chooses which layers' ink acts as a wall. See below.
Bridges small breaks in an outline. See the mechanism below.
Grows the finished fill past the line, or shrinks it back. Positive values dilate the coverage, negative values erode it.
Boundary scopes
The scope picks which ink closes the region. It does not change where the paint goes: the fill always lands on the active draw target regardless of the scope.
Only the active target's own ink bounds the fill.
The active main layer, all of its sub-layers, and its mask all act as walls. An outline drawn on the main layer therefore closes a fill made from a paint sub-layer.
Every visible layer, plus their sub-layers and masks, acts as a wall. Hidden layers do not close regions.
Within the chosen scope the flood only counts ink that could plausibly bound the tapped wall: volumetric strokes, existing fills and empty strokes are ignored, and ink on planes that are not close to parallel with the tapped one is excluded. Closing a region across angled planes is the job of the fold fill described below.
Close gap and Expand
The two sliders act at different stages of the flood, and the order matters.
Thicken the walls
A Close gap above zero dilates the boundary coverage by that many pixels, fattening every
wall until small breaks are bridged. If the tapped seed point now falls on a thickened wall,
it is nudged to the nearest open pixel within gap + 3.
Flood
The region is flooded from the seed.
Abort on a leak
If the flood reaches the outer border of the ink's own extent, the fill is abandoned — an unclosed loop produces no fill rather than a flooded canvas. Sides clamped by the window are exempt from this test.
Grow back
The coverage is grown back by gap + 2, undoing the inward thickening and tucking the fill
two pixels under the line's antialiased edge so no pale seam is left.
Apply Expand
Only now is Expand applied: positive values dilate the coverage, negative values erode it.
If the flood leaks at the current Close gap, it is retried once at a fixed fallback of 12 px. A genuinely open shape leaks at both settings and stays unfilled.
Dilation is square, not circular
Both Close gap and Expand grow and shrink the coverage on a square (Chebyshev) footprint. Corners therefore extend slightly farther than a circular offset of the same radius would.
A fill becomes paint
A fill is raster ink. Whatever the shape of the region it landed on, the bucket produces an ordinary painted fill, not a piece of geometry: you can erase it, blend it, put a blend mode on it, and it reloads as paint.
That matters most in three dimensions. A fill that stayed as a mesh behaved unlike everything else on the layer — the eraser would not bite it and it carried geometry nothing else needed.
How the region is laid down depends on its shape, and the bucket works through the cases in this order:
| The region is | What is laid down |
|---|---|
| On a bent drawing surface — a cylinder, a sphere, a curved grid | One raster fill in that surface's own space, so it follows the curve exactly from every angle. |
| Flat | One raster fill on its plane. |
| A fold — a handful of substantial flat walls meeting at angles | One raster fill per wall. The pieces overlap very slightly along each crease so no hairline of background shows through. |
| A smooth or irregular surface that would shatter into slivers if it were cut up | A conforming three-dimensional fill whose triangles are the surface, so it hugs the form from every angle. |
The last case is the exception rather than the rule, and it is what a paint surface built over freeform ink usually produces.
The fill follows the ink, not the grid
A fill lands on the surface the outline was drawn on, not on the layer's current drawing grid. Strokes record the surface they were made on and keep it, so a fill inside a shape you drew on a cylinder is laid on that cylinder even if the grid has since been flattened — the same rule that governs strokes themselves.
Filling a fold
Fold filling is attempted from the tap ray rather than from a raycast seed point, so it works from viewing angles that make the drawing grid edge-on — a fill tapped from directly above still lands. Its boundary chain is seeded by screen distance to the tap.
Build paint surface
Ink drawn across several planes — a contour drawing, an outline built by orbiting between strokes — describes a surface no one flat plane represents, and the bucket has to guess at it. The Fill panel therefore carries the same Build paint surface control the Select panel does: work the surface out once, explicitly, and the bucket fills on it instead of guessing.
Select the strokes that describe the shape and tap Build paint surface; the surface is invisible and is never drawn. 3D shots only.
The replace rule
Re-filling a region replaces the existing fill; it does not stack a second one on top.
When a new fill is inserted, any existing fill that is coplanar with the new surface and whose bounds overlap by at least 90% of the smaller area is removed first — that is, a second bucket over essentially the same region of the same wall takes the place of the first. Without this, two coincident fills would both render and the older one would show through.
A 3D fill mesh occupying the same loop is likewise removed, unless that mesh has been sculpted, in which case the sculpted work is preserved.
A new fill is inserted behind the layer's ink, so outlines stay on top of the colour.
What a tap resolves to
The tap resolves its surface enclosure-first: the front-most surface that encloses the tap point wins, then the surface of the stroke under the pointer, then the active drawing surface. The attempts run in order — a flood confined to the tapped wall, then a fold fill, then a flood across the tapped orientation's parallel planes, then a screen-space loop fill. If none of these apply, the fill coats the model under the tap, or failing that the whole 2D frame, inserted behind the ink.
Gestures
Fills the region under the pointer. The fill is deferred to touch-up and only runs if the touch travelled less than 12 points.
Fills every enclosed region the pen crosses. The drag needs at least 12 points of travel to begin, then probes every 10 points. Each region fills exactly once per drag.
Both are suppressed while a second finger is down, so a two-finger orbit never drops a fill.
QuickStrip and Sub Tool
The QuickStrip carries no sliders for Fill — only the colour well. The gap-close and expand controls are shaped nothing like a size rail and live in Tool Options. Fill has no sub-tools.