Editing Edges and Flaps

Editing Edges & Flaps

After you unfold, the 2D canvas lets you refine exactly where the pattern is cut and where glue tabs (flaps) go. This page is the full reference.

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Edge types

Every mesh edge becomes one of three kinds in the pattern:

Type	Meaning	On paper
Fold	Interior seam kept attached — the two faces stay in one piece	Dashed fold line
Cut	Seam separated — the faces belong to different pieces (or the same piece via a tab)	Solid cut outline
Border	A mesh boundary with no adjacent face	Solid outline; can carry a tab

Click an edge on the canvas to toggle it between fold and cut. Cutting more edges splits the pattern into more, smaller pieces; folding edges merges pieces back together.

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Joining and disjoining pieces

• Join — reattach a piece to a neighbour along a shared edge. A preview arrow shows where and how the piece will fold in before you commit.
• Disjoin — detach along an edge, turning a fold into a cut.

Use this to control how the model breaks apart — e.g. keep a face group together so it folds as one flap, or split a piece that overlaps itself.

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Glue tabs (flaps)

Tabs are the extra paper you fold under and glue. Two things control them: the shape (global) and the per-edge mode (override).

Tab shapes

Choose globally: Trapezoid (default, most forgiving), Rectangle, or Triangle. There's also an alternate-flap mode that automatically staggers tabs from one face to the other along a seam so two tabs never stack on the same edge.

Per-edge flap modes

Right-click / open the flap editor on an edge to override the global behaviour. The mode set depends on whether the edge is an inner (shared) edge or a border edge.

Inner edge (cut edge shared between two faces):

Mode	Effect
Default	Follow the global alternate-flaps logic
SwitchPosition	Swap which of the two faces carries the tab
OnOn_ThisSide	Tab on the face you designated as "this side" when clicking
OffOn_OtherSide	Tab on the partner face only (suppress this side)
OffOff_NoFlap	No tab on either side of this edge
OnOn_BothSides	Tabs on both faces of the edge

Border edge (mesh boundary, no partner face):

Mode	Effect
Border_MountainFold	Add a tab annotated as a mountain fold
Border_ValleyFold	Add a tab annotated as a valley fold
Border_NoFold	Add a tab with no fold annotation
Border_NoFlap	Explicitly no tab

The "this side" / partner distinction (used by OnOn_ThisSide, OffOn_OtherSide, SwitchPosition) is set by which face you click when choosing the override.

Flap overrides are saved inside the .4hu project bundle, so your customizations survive a reload — and are cross-platform between Windows and macOS.

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Moving, rotating, grouping pieces

• Drag a piece to reposition it on the page.
• Rotate handle on a selected piece spins it (useful for packing).
• Lasso-select multiple pieces with a rubber-band drag; hold Shift to add to the selection.
• Group / Ungroup — grouped pieces move and rotate as one unit; groups persist in the .4hu.
• Right-drag pans the canvas; scroll zooms.

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Undo / Redo

Edge toggles and flap overrides are captured as lightweight snapshots, so Undo / Redo step through your edits safely.