4.3.16-beta is up now and it has sliders! 🎆 A slider is a type of constraint that applies an animation. This is useful for all kinds of things. For example, you can use an animation with a bunch of attachment keys, then use the slider to choose which to use. You could also use a slider to apply poses or facial expressions -- anything you can key. Also, since you can animate the slider position, you can interpolate between adjacent poses.
hwadock Using sliders you can change colors and attachment visibility (and anything else!). Next we'll add the ability to map a bone transform property to change the slider value. Then you'll be able to use sliders for all kinds of rigging. For example, you could animate muscles bulging and have that happen automatically when an arm bends. It's very powerful and there are a TON of applications.
Note that sliders aren't intended to replace AnimationState or be used like an animation mixer. You can key sliders such that it simulates animation playback, but it's less powerful and less flexible compared to playing animations on multiple tracks with AnimationState.
Also 4.3.16-beta is more efficient, in some cases having 20-30% higher frame rates for very large projects, both in the editor and at runtime.
ALSO in 4.3.16-beta we've improved physics when the rendering rate is higher than the physics rate. You can see the problem in 4.2 by setting the speed to 10% on the Playback view -- it makes the physics motion choppy. Now in 4.3 it's super smooth! This allows you to reduce the physics FPS so physics uses even less CPU. For example, the celestial-circus example project still looks good even with all the physics FPS changed from 60 to just 10, plus it is still smooth at 10% playback speed.
Among a number of smaller changes, we've added 8 example projects to the Examples
tab on the welcome screen, and each has a corresponding Animating with Spine
video covering various animation theory topics.