Brush tool

Paint with pressure-sensitive brushes on pixel layers, or lay down crisp filled vector strokes on a Shape layer.

The Brush tool paints on whichever layer is selected, and what it produces depends on the type of that layer. On a Raster Cells or Pixel layer you get pixels; on a Shape or Vector Cells layer you get real vector geometry with a crisp outline you can still edit afterwards.

Press B to reach the Brush. Colour comes from the Color panel: the brush uses the active colour slot at the moment the stroke starts, so switching colours mid-stroke has no effect until the next one.

Which layer the brush paints on#

• Raster Cells or Pixel layer: paints pixels into the layer's cell for the current frame.
• Shape or Vector Cells layer: paints vector blobs (see below).
• Any other layer, or nothing selected: paints pixels, or vector, depending on the New Layer option; on the first stroke it creates the layer you chose.
• A locked or hidden paintable layer: nothing is painted. The canvas shows the banner "No paintable layer active. Select or add a Raster/Vector layer." for two seconds.
• The GPU brush engine cannot run, or the layer is too large for it on your graphics card: a banner on the canvas says which. Painting and erasing brushes then paint with a plain round tip, and smudge, deform and watercolor brushes cannot paint at all. When the engine cannot run, update your graphics driver and restart Celas Studio.

The options bar#

The bar opens with the tip swatch, the preset combo and the Brush Studio button, then the fill and stroke colours, then the numbers you reach for while painting. Size, Opacity and Flow belong to the preset and are saved with it, so changing them edits the brush you have selected rather than a temporary tool setting. Streamline and Smooth are global: they stay the same whichever brush you pick.

The two colour swatches are the colours the next stroke takes. With a Shape layer selected they are that shape's fill and stroke, gradients included, and its stroke Width sits beside them, so you can restyle it without leaving the brush. Where the brush paints pixels, on a Raster Cells or Pixel layer, they are the Color panel's Color 1 and Color 2 as plain colours, with no None and no gradient to pick.

While Streamline is above zero you can see the string as you draw: a line runs from the pen to the brush, taut while it is pulling and slack while it is not. The brush follows the curve your hand actually made, so fast strokes keep their shape instead of turning into straight facets.

The chevron at the end opens the settings you set once and then leave: Symmetry, Draw Into and New Layer. A dot on the chevron means something inside it is off its default, so a symmetry you turned on last week cannot silently change every stroke.

With Symmetry on, a magenta axis line and a round centre handle appear on the canvas. Drag the handle to move the mirror point anywhere, even off the canvas centre; double-click it to put it back in the middle. The mirrored half follows the pen's tilt as well as its position, so it leans the right way.

The bar also has a Blend Mode list for the Brush tool. It is the same setting Brush Studio edits, so the two always agree. The list holds 29 modes: Normal, Dissolve, Behind, Clear, Darken, Multiply, Color Burn, Linear Burn, Darker Color, Lighten, Screen, Color Dodge, Linear Dodge (Add), Lighter Color, Overlay, Soft Light, Hard Light, Vivid Light, Linear Light, Pin Light, Hard Mix, Difference, Exclusion, Subtract, Divide, Hue, Saturation, Color and Luminosity. All of them are computed on the graphics card, in Pixel Mode and for watercolor too.

The cursor#

The tip is drawn as its own silhouette, so a chisel, spatter or foliage nib is recognisable before you lay down a single dab. Holes and separate islands in the tip come through as well, and the outline is squashed and turned by the preset's own Roundness and Angle. A preset with no bitmap tip, the procedural soft disc, stays a plain circle, which is exactly what it paints.

Around it, a second circle shows the full footprint including scatter and size jitter. That one stays a circle by definition: it is the reach of the jitter, not the shape of the nib, and it only appears when it is meaningfully bigger than the tip. Both are grey normally and red whenever Eraser is on.

Pressure and tilt#

A graphics tablet feeds pressure and tilt into every point of the stroke, and barrel rotation too on pens that report it. The preset decides what they drive: size, opacity or any other dynamic. Pressure is read for every sample the pen reports, not once per screen frame, so it changes smoothly and a pen lift tapers naturally. With a mouse, or with Pen Pressure off, the preset draws its own taper instead.

If you never reach full size, or have to press very hard to get there, calibrate your pen in Preferences ▸ Pen. It sets how firm a press counts as full pressure and how soft or firm the pen feels, for every tool at once.

Tilt reaches most of the library. Lean the pen over and a round brush opens onto its side: the mark widens and flattens, and the same paint spreads over more paper. Pencils, charcoal, chalk and crayon shade with the side of the lead, and the mark points the way the pen points.

Painting on a Shape or Vector Cells layer#

On these layers the brush is a vector blob brush: the blue preview you drag is the exact region that will be added, mirrored copies included. It answers to pen pressure too, following the preset's Size dynamic point by point, and a mouse stroke tapers in and out. On release the region is merged into the target shape as one compound shape, so overlapping strokes become a single clean silhouette rather than a stack of outlines.

On a Shape layer the target is simply the shape you have selected, however it was drawn. Painting on a rectangle, or on a path you made with the Pen, welds the stroke into that same path: what you get is one outline around the combined silhouette, not the stroke sitting on top of the old edge. The layer keeps its transform, its keyframes and its effects, so an animated shape carries on animating. Only when nothing usable is selected does a stroke create a shape of its own.

A stroke that lands away from the shape cannot be welded to it, so it stays a separate closed outline inside the same layer, and a stroke that loops around empty space leaves that space as a hole. Both are what the merge should do; painting across the gap afterwards joins them into one outline.

The merge is a true boolean union in exact integer arithmetic: it never moves a point of your outline, it only adds the intersections. Its fill rule is switched to non-zero so crossing strokes add up instead of cutting holes, and a shape that has no fill does not take the stroke: the stroke becomes a shape of its own, unless the shape is empty. Keep a copy of a shape you still want to edit by its original handles.

The union writes polygon rings, so the result is refitted as bezier curves before you ever see it. Nodes land only where the neighbouring handles can carry the curve, genuine corners are found and pinned Sharp, and a painted stroke comes back as a handful of curves rather than the thousand-odd anchors the raw union would have left. The error budget is derived from the brush radius and clamped well under a pixel, and the fit refuses to run at all once it would cost a shape more than a fraction of its own diagonal, so a hairline stroke is never eaten by its own smoothing. Press Simplify on the Node tool when you want fewer points still.

The tip shapes the stroke#

A preset with a real bitmap tip stamps that tip's outline along the path and unions the stamps, so a chisel or a flat nib leaves a vector stroke with the same silhouette the cursor showed and the raster brush would have painted. A preset with no tip is the procedural soft disc, which is a round offset by definition, so those keep the faster round-offset path and come out identical either way.

What the vector side stamps is the tip's envelope, not its every speckle: islands and specks are dropped and the outline is held to a couple of dozen points. Per-bristle grain is a raster property, and a rough nib's true silhouette is a fractal edge that no editable path can carry. The envelope keeps what vector can express, a chisel, an oval, a flat or a blob, and leaves the texture to the pixel side.

Colour is the one thing that still starts a new shape: a path can hold exactly one fill, so paint merges only into a shape whose fill already matches your active colour. Paint a different colour and you get a new shape instead of having the old one repainted.

With Eraser on, the same region is subtracted instead. Erasing a shape away completely removes it.

On a Vector Cells layer the brush works per cell and has to find its own target, so there it merges only into shapes an earlier brush stroke made, and only when their fill colour matches your active colour. Line art you drew on the cell with the Pen or the Pencil is never absorbed, and picking a different colour starts a new shape, which is what keeps line and fill separable on the same cell. On either kind of layer, a shape whose points are keyed never takes a stroke, because the next frame would write its keyed outline back over it: the stroke becomes a shape of its own beside it.

Presets and Brush Studio#

The combo at the left of the options bar picks the active preset and previews each one as a stroke thumbnail. The full preset library, with categories and the right-click New, Duplicate and Delete commands, lives in the Brushes panel; every parameter of the active preset is edited in Brush Studio, which the icon button beside the combo opens. Both have their own pages.

The tip swatch sits beside that pair and opens the tip popup: the tip shape grid, Tip Angle, Angle Jitter, Scatter and Direction Follow. It edits the active preset rather than holding tool-local values, so what you set here is what the preset paints with everywhere. The Pencil, Eraser and Smudge bars carry the same popup.

The Brush keeps its own preset, separate from the ones the Pencil, Eraser and Smudge remember, and it survives closing the app. Coming back to the Brush restores its card and jumps the Brushes panel to the matching family. The Brush draws from the whole library, so no category is off limits to it.

Working with selections and snapping#

When a pixel selection is live, the stroke is clipped to it, and clipped live: paint stops at the marching ants while you draw rather than spilling over and snapping back when you lift the pen. This holds on both sides of the tool, the raster stroke and the vector blob, so painting inside a selection behaves the same whatever kind of layer you are on. With snapping on, Snap to Grid enabled and the grid visible, brush input is snapped to the grid as you draw.