What does preroll do in cloth simulations?

I’m familiar with the general concept from Poser 5. There it runs the simulation for a specified number of frames prior to the beginning of the actual animation. But when I noticed it and tried it in Blender it didn’t do anything.

I did a google search and it led me to an archived post explaining how to use it. I followed the instructions (negative start frame for the cache, set current frame to cache start - 1, and baked) and it did exactly what I needed it to.

However, I realized that preroll was still at 0 since I forgot to change it. I set it to 100 frames, baked again, and there was absolutely no difference. The cloth acted the same way, which I expected, but it still had 172 frames in memory so I don’t think it’s a memory saving feature.

Is it just not hooked up to anything at the moment or is there something I’m missing?

The idea is –
suppose your character starts walking at frame 1 to frame 100. that is the settings for the cloth on his pants. But you may want the pants to start at with realistic wrinkles , so you preroll the cloth for a few frames to give a realistic starting point, before the animation begins.

Did you put in positive or negative frames for the preroll?

I’m familiar with the concept of preroll. I just can’t tell what it does in Blender. Setting the start frame to a negative value for the cache works the same with and without preroll and preroll itself doesn’t seem to do anything.

I had to put a positive value for the preroll. It won’t accept anything less than 0.