When the value specified in Spacing is greater than half of the target path's length, irregular motion may occur in the position animation.

[misaki-eymard]

Description:
If the target path is a closed path, specifying a value for Spacing in a path constraint that is greater than half the length of the target path can cause the constrained bones to wobble and move erratically when creating a position animation that circles the path. For example, the two skeletons shown in the GIF animation below both have the same path and the same bones, but the left side has Spacing set to 78.96% and the right side has 50%:

In the skeleton on the left, the first bone (yellow bone), constrained by the path constraint, moves smoothly, but the second bone (purple bone) moves unevenly.

It does not matter what type of Spacing is specified for this problem to occur, whether Length, Fixed, Percent, or Proportional, if the value exceeds half the length of the target path, this kind of irregular movement can occur.

This problem also occurs when trying to move the Position slider on the tree view without animating it with keys:

Expected behavior:
Smooth position changes even when Spacing values exceed half the length of the target path.

Steps to reproduce:
Using a reproducible project:

1. Download the attached .zip file: path-spacing-issue.zip
2. Open the included Spine project with Spine 4.2.36 and play the animation or move the Position slider of the path constraint “circle”.

You can confirm that this problem does not occur by reducing the value of Spacing to a value lower than the length of the target path (576.5).

The versions of Spine that can reproduce this issue:
It has been confirmed that this problem can be reproduced with 4.2, 4.1, 4.0, and 3.6 (3.7 and 3.8 are unconfirmed).

This issue was reported in the following thread on the forum:
https://esotericsoftware.com/forum/d/26999-weird-behavior-regarding-paths-with-constant-speed

[misaki-eymard]

Sorry, I missed one condition: To reproduce this problem, the Constant speed option must be checked in the path attachment options. If you uncheck it, the problem will not occur.