Sometimes cloth animation starts immediately, sometimes only after a first run.

I’ve been noticing this for awhile now, and I can’t figure it out.

If I start a new project with cloth animation, I can hit ALT-A to test out some cloth animation and the animation will begin right away. As long as I let the animation run all the way through, until it starts repeating from the beginning, I can then interrupt it with ESC. Subsequent animations will also start immediately upon hitting ALT-A.

But if I interrupt the animation with ESC before it gets through that initial run, something weird happens on subsequent invocations of ALT-A.

The effect is this: I’ll hit ALT-A, and the cloth won’t move until after the timeline runs all the way to the end. Then when the marker goes back to frame 1 the animation finally starts. After this effect happens once, all future invocations of ALT-A will behave the same way, running through the whole animation without the cloth moving at all, and only then doing the animation on the second run-through.

I haven’t narrowed down exactly what causes this, or what causes any variations that I’ve seen. For example, sometimes the animation will be stationary for part of the way through the timeline, and then in the middle it’ll suddenly go kablooey, as if the cloth physics caused the fabric to explode completely. Then after that run-through, as the marker returns to the first frame, the cloth animation happens normally.

I’m curious if anyone else sees this and why it takes place. But mostly I’d like to find out a way to undo it - to make the animation happen correctly and immediately when I hit ALT-A.

Be well,

I figured out how to avoid this problem. If I’m at frame 0 when I hit ALT-A then the animation plays normally. But if I’m at frame -1 when I hit ALT-A, it won’t. Bizarre.

My workaround is to make sure I’m always at frame 0. To do that I use SHIFT-LEFT_ARROW as opposed to using the mouse to click on the frame I want. The mouse method is inexact, which is why I encountered the problem in the first place. The hotkey method always gets me to the right spot.

This is not a workaround, this is how to do it :slight_smile:

The “problem” you encountered is, that blender can’t calculate the simulation if it starts midway in it - because blender don’t know what already happened to the cloth.

So just start always at the start frame of your cloth cache (usually frame 1 if you haven’t changed it)…

But frame -1 isn’t midway in the animation - it’s before it. I could understand if blender got confused if I started the animation at frame 20 or something. But starting at frame -1, I’d expect it to do nothing for one frame, and then hit frame 0 and begin the animation.