Knife tool

Cut a shape in two along a line, or trim a line back to where it crosses another.

The Knife (Shift+K) cuts artwork in two, vector and pixel alike. You drag a cut line across the canvas and nothing happens until you let go: the line you see while dragging is only a preview, so you can start again by dragging somewhere else. It is drawn red, and turns green the moment it lies where it would actually cut something.

Two pills in the options bar decide what the cut does and how you draw it.

Split and Trim#

Splitting a shape#

Select the shape first: Split works on the selection. Drag your cut and release: the shape becomes two or more pieces, all selected afterwards so you can move them apart straight away. Each piece keeps the original name, fill, stroke, opacity and blend mode, and each is an ordinary shape you can go on editing with the Node tool. Their outlines are refitted as bezier curves, so a curved edge that was not touched by the cut comes back as curves rather than as a run of hard nodes.

An open path is cut too, and it is cut differently. There is no interior to divide, so instead the curve is subdivided exactly where your cut crosses it and each run of points is handed to its own shape. The geometry is exact: the two halves of a split curve reproduce the original, so a line cut in the middle of a bend does not straighten there.

A straight Split cuts along the whole infinite line, not just the segment you drew, which is why the preview shows a faint red extension running off both ends. You only need to drag across the part of the shape you care about. If the line misses the shape entirely, that shape is left alone.

Trimming a line#

Trim is for cleaning up rough line work, and it needs nothing selected: it looks at every visible, editable shape on the canvas. Cross a line with the knife and the piece between the nearest crossings on either side is deleted. An open end that comes close to another stroke counts as a crossing too, so an overshooting tail can be trimmed against the line it overshoots.

A trimmed line comes back open and unfilled: a line is still a line afterwards. A filled shape keeps its fill and stays closed, because the trim took a bite out of it rather than turning it into a stroke; it used to come back empty, which read as the knife having deleted it. If nothing bounds the place you cut, the stroke is divided in two instead of losing a piece. The first piece stays on the original layer; the second becomes a new layer.

Cutting a pixel drawing#

On a Raster or Pixel layer the same drag cuts the drawing in two along the line, and it works on any brush, scattered and textured ones included. The two halves land as separate layers the way a split shape does, so you can move one away from the other straight afterwards.

What happens to fills and strokes#

• Split on a closed shape: both halves stay closed and keep the original fill and stroke.
• Split on an open path: each run of points becomes its own open path, and every piece keeps the original name, fill, stroke, opacity and blend mode. Holes and boolean pieces are not carried over, since a piece of a line has no interior to hold them.
• Trim on a line: the surviving arms are open and unfilled; their stroke style is kept.
• Trim on a filled shape: the remainder stays closed and keeps its fill.
• Either mode: the pieces keep the keyframes, effects, dash pattern and clipping that belonged to the shape they came from.

Limits#

• Split works only on what is selected.
• A Split that would leave one side empty is skipped, so grazing an edge does nothing.
• A freehand Split is applied only when it actually produces two or more pieces.
• The knife has no modifier keys and does not snap. A cut that hits nothing simply ends with no message, and Escape cancels a drag in progress.