Hmm, it could be a spine-lua bug. badlogic can check it out as soon as he can (he's probably recovering from New Year's Eve :drunk🙂. You don't have to do anything for mixing other than specify the mix duration.
Note AnimationState setAnimationByName
takes only 3 arguments. AnimationState addAnimationByName
takes 4.
Is love.keypressed
called every frame? If so, you don't want to set the new animation every frame.
You can try:
local entry = playerSkeleton.state:setAnimationByName(0, "walk", true)
print(entry.mixDuration)
If you don't see the right mix duration, something is bugged with how it gets set or configured. You can also try:
local entry = playerSkeleton.state:setAnimationByName(0, "walk", true)
entry.mixDuration = 0.25