Spine Two-Bone IK Will Not Stretch? Check Softness First

The target moves beyond the arm reach and Stretch is enabled, yet the hand stays behind. Display the bones and target in a project copy. Record the bone tip separately from the hand artwork. A correct bone tip with displaced art calls for an attachment check after the solver result is preserved.

Record the applicable conditions

The official reference documents two cases in which two-bone IK stretch is not applied: positive softness and nonuniform local scale on the parent bone. Log the constrained parent and child names, Stretch, Softness, Mix and the parent local X/Y scales. Read the values used by the active constraint. Keep this investigation scoped to two-bone IK and verify the behavior for the version in use.

Run three controlled passes

Build a baseline with nonzero bone lengths, positive uniform parent local scale, zero softness and full IK mix. Move the target gradually beyond maximum reach and record the bone tip. In a second copy, restore only the original softness. Return to baseline for a third pass and restore only the original nonuniform parent local scale. Observe when stretching stops. Changing the artwork or bone lengths at the same time would obscure this comparison.

Retain the motion checks

After the distant-target test, move inward and outward and restore the normal animation. For an elbow bending the wrong way, use the related diagnostic guide for Positive rather than treating stretch as a bend-direction control. Hand off editor and runtime versions, constraint settings and captured poses. Review compatible asset appearance in the Spine Workbench, then validate constraint solving inside the receiving project.