Skeir I notice when using actual rotation the effect feels more appealing compared to gradually changing the ScaleX from 1 to -1.
Did you just interpolate ScaleX linearly from 1 to -1, or did you use ScaleX = cos(angle)? The latter should look more convincing. Lighting (due to angles) and Z values will still be different to real rotation obviously.
Mario I'm not super familiar with spine-unity, so I'm not sure how it solves the attachment draw order problem in 3D. @Harald can you elaborate how you do sort order in 3D in the Unity runtime?
Actually in spine-unity, when adding z-spacing and rotating the skeleton 180 degrees around the Y axis, the attachment placement order would end up being be incorrect. Like depth order 123 resulting in 321 when viewed from behind. However, when not writing to the Z buffer, the draw order inside the mesh is still the same, draw order 123 still rendering in order 123. Thus unless ZWrite is enabled, the result will look good when rotated, visible attachment order is not inverted.
What users can do to compensate incorrect depth order is to programmatically change the z-spacing from the normal negative value to a positive one once the angle is greater than 90 degrees (and less than 270).
In case I misunderstood the question and it's regarding sorting order of the whole MeshRenderer skeletons inside a scene: Unity let's you change sorting from the default sorting by depth along the camera axis to along a custom user-defined axis (useful for isometric games, using the Y up-axis then). The center (not the origin unfortunately) of the MeshRenderer's Mesh will be used as position for sorting.
