Bend: tails, ropes and soft parts that flex

What a bendable part is

A stiff part rides on one bone and turns as a plate. A bendable part (a weighted mesh in Spine terms) is carried by several bones at once: turn one of them, and the art bends smoothly between it and its neighbours.

It is the right choice for anything long or soft: a tail, a long neck, a tentacle, a ribbon, a rope, hair, a soft body that wobbles.

Asking for it

• Two bones are enough for a rope that folds in one place, a tail takes 3–5, a long tentacle 5–6.
• A bend has a limit: at a joint the art narrows as the angle sharpens — to 0.87 of its width at 60 degrees. For a tight curl ask for more bones rather than a sharper fold.
• Eyes, a mouth or a pattern on a soft body must be glued to the same bones. Say “glue the eyes to the body”; left on a bone of their own they slide off as soon as the body bends.

Other ways a part changes shape

• A turn: a flat picture turns as if it had depth, up to 45 degrees — a head turn, a nod.
• A wave: a flag, a ribbon, hair or water ripples while one edge stays put.
• A shape by points: name a point on the picture and where it goes — a blink, a smile, a breath.

A part has one such shape motion per animation: asking for a wave replaces an earlier turn.

The Bend mode and the brush

Once the rig has a bendable part, the switch under the player gets a third position, Bend. Select a bone, and the canvas shows how much it influences each bendable part — brighter means more.

• Drag across the part to add the selected bone’s influence there; ⌥ + drag takes it away.
• 25 · 50 · 100 % set how strong the brush is, S · M · L how wide.
• The chat stays the main way: the model sets the influence for you, and the brush is for the last touches. On a phone the mode shows the influence but does not change it.

Export

A bendable part is standard Spine 4.2 data. Runtimes play it as they play any other, and the Spine editor opens it if an animator wants to refine the influence there.