Negative Pre-roll Not Allowed on Cloth #33469

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David Brennan · 2012-12-11T01:53:58+01:00

David Brennan commented

2012-12-11 01:53:58 +01:00

%%%When a Cloth Physics trait is applied to a Mesh, there is the "Pre roll" option in its main Physics settings. This is obviously needed because, most of the time, the Physics takes 100 to 200 frames of simulation before it begins to look correct.

But with the Cloth, if one's animation begins prior to that priming period of 100 to 200 frames, then their render will begin with the cloth looking crazy. (I just did an animation of a superhero cape with a Cloth Physics property and had this problem.)

Of course, the obvious work-around is to bump all the animations and keyframes back 200 frames and allow the Cloth to look correct. However, there are three problems with this:

Some actions (such as the timing of Particles) are not Keyframed. Therefore, if one has to shift all of their animations back to accommodate the Cloth priming period, it can be very, very time consuming and frustrating. You cannot just grab the Keyframes in the Dope Sheet, as one might hope.
If there are actions in the NLA, then shifting them can also turn out improperly.
It's a funky work-around to begin with, and simply allowing Pre-roll would be superior.

As it is, the pre-roll option is visible there in the Cloth Physics tab, but it's mostly useless now. So hopefully it can be put to use.

Blender 2.64
Windows 7 64-bit%%%

%%%When a Cloth Physics trait is applied to a Mesh, there is the "Pre roll" option in its main Physics settings. This is obviously needed because, most of the time, the Physics takes 100 to 200 frames of simulation before it begins to look correct. But with the Cloth, if one's animation begins prior to that priming period of 100 to 200 frames, then their render will begin with the cloth looking crazy. (I just did an animation of a superhero cape with a Cloth Physics property and had this problem.) Of course, the obvious work-around is to bump all the animations and keyframes back 200 frames and allow the Cloth to look correct. However, there are three problems with this: 1) Some actions (such as the timing of Particles) are not Keyframed. Therefore, if one has to shift all of their animations back to accommodate the Cloth priming period, it can be very, very time consuming and frustrating. You cannot just grab the Keyframes in the Dope Sheet, as one might hope. 2) If there are actions in the NLA, then shifting them can also turn out improperly. 3) It's a funky work-around to begin with, and simply allowing Pre-roll would be superior. As it is, the pre-roll option is visible there in the Cloth Physics tab, but it's mostly useless now. So hopefully it can be put to use. Blender 2.64 Windows 7 64-bit%%%

David Brennan commented

2012-12-11 01:53:58 +01:00

Changed status to: 'Open'

David Brennan commented

2012-12-11 01:55:28 +01:00

%%%NOTE: This belongs in the Physics category. Sorry I forgot to specify that.%%%

Brecht Van Lommel commented

2012-12-18 16:47:12 +01:00

%%%The tooltip for this option was wrong, this actually specifies the number of frames to do preroll, not the start frame. I don't know if it's working correct though, if I enable Allow Negative Frames in the user preferences and go back, then it indeed seems to start the simulation earlier. But it seems a bit strange that this would be needed, though given the current physics point cache design I'm not sure how it would work otherwise.%%%

Brecht Van Lommel commented

2012-12-24 13:14:54 +01:00

%%%Thinking about this further, this is a limitation of the design that I wouldn't consider a bug. It's inconvenient having to enable negative frames but they work and mean you don't have to move any keyframes to start the simulation earlier. So will mark as todo item.%%%

Brecht Van Lommel commented

2012-12-24 13:14:56 +01:00

Changed status from 'Open' to: 'Archived'

Brecht Van Lommel closed this issue

2012-12-24 13:14:56 +01:00

David Brennan commented

2012-12-24 14:53:33 +01:00

%%%I was actually unaware of the "Allow Negative Frames" option in the User Preferences, but was sparked to find it after you posted here. (Here it is at the Wiki: http://wiki.blender.org/index.php/Doc:2.6/Manual/Preferences/Editing)

But even after enabling this, the Timeline only allows you to go back as far as frame #0. (This is Blender 2.65 for Windows 64-bit.) So as I'm now toying with it, I don't see how this solves the issue in practice.

So what is the process you would recommend? Again, suppose one has a character with a cape (via Cloth Physics), or a scene with gently blowing curtains (also with Cloth Physics), and they would like to start rendering at frame number one, rather than having to push everything back 200 frames to allow the Baking to look proper?%%%

%%%I was actually unaware of the "Allow Negative Frames" option in the User Preferences, but was sparked to find it after you posted here. (Here it is at the Wiki: http://wiki.blender.org/index.php/Doc:2.6/Manual/Preferences/Editing) But even after enabling this, the Timeline only allows you to go back as far as frame #0. (This is Blender 2.65 for Windows 64-bit.) So as I'm now toying with it, I don't see how this solves the issue in practice. So what is the process you would recommend? Again, suppose one has a character with a cape (via Cloth Physics), or a scene with gently blowing curtains (also with Cloth Physics), and they would like to start rendering at frame number one, rather than having to push everything back 200 frames to allow the Baking to look proper?%%%

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Negative Pre-roll Not Allowed on Cloth #33469