The idea is that you usually don't want frame 0 going off screen. If we always zoom centered on the timeline position, that would happen every time you zoom in. There's a thread about it here:
Zooming in the dopesheet

I knew you would have an explanation for this

And you are so right

Woo! :fyeah:

Hello. I don't use Spine and don't know how the zooming worked 3 years ago but I like how opinionated @Nate is 8) Could you or someone explain how the "super awesome" Spine zoom works? Is it zooming in at the cursor position and zooming out at the center of the viewport? Do you (Nate) still stand by it after all this time or did it turn out to be a bad idea after all?

Cheers

Spine's zoom works great! You can try it out in the Spine trial:
Spine: Trial Download

I see it works great but what's it doing on zoom out? It seems to be centered on not the cursor or the center of the viewport, but a mirror image of the cursor on the opposite side of the center of the viewport. Is that correct?

Sort of:

To zoom in, place the mouse on what you'd like to see larger and scroll the mouse wheel upward.

To zoom out, place the mouse near the edge of the screen where you want to see more and scroll the mouse wheel downward.

User interface - Spine User Guide: Zooming

Maybe the details are a bit of secret sauce? Thanks for responding though. I'll go with my mirror image theory, which seems to be equivalent to zooming out at the cursor position except panning in the opposite direction to what that would normally do.

Well it comes down to math in the end. :p It's using the screen center as zooming straight out (what most software does, which sucks) and the distance from the center to the mouse to shift the view as it zooms.

The only other software I know with zoom this sophisticated it Supreme Commander. Check it out, it's pretty awesome! 8)