"Follow path" constraint subframes calculated incorrectly #29113

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Miika Hamalainen · 2011-10-31T18:42:39+01:00

Miika Hamalainen commented

2011-10-31 18:42:39 +01:00

%%%Subframes calculated for "Follow Path" constraint's "Offset" property are calculated incorrectly, making object appear ahead it's real position. Same thing probably happens with other Blender components as well, but at least with this one. :)

How to reproduce:

Open the "curve_subframe_bug.blend". (Attachment)
Render the image. It looks something like this: http://www.miikah.org/blender/curve_subframe_bug.png

Red cubes are position markers showing where object should be each frame.
Blue cube's location is animated by keyframes. It's interpolated correctly.
Green cube is animated by the follow path constraint. It's drawn more ahead for every subframe.

However, if you render whole frames or preview it through the timeline, it's shown correctly.

That scene is rendered with full sample motion blur of 6 samples and shutter time of 3 frames. So from the code point of view, the last "blur sample" is rendered at full frame (scene->r.cfra) of 1, and subframe (scene->r.subframe) of 3.0.

(This isn't isn't a bug in full sample motion blur calculation but in animation system. I originally run into this while testing Dynamic Paint subframes. :)%%%

%%%Subframes calculated for "Follow Path" constraint's "Offset" property are calculated incorrectly, making object appear ahead it's real position. Same thing probably happens with other Blender components as well, but at least with this one. :) How to reproduce: * Open the "curve_subframe_bug.blend". (Attachment) * Render the image. It looks something like this: http://www.miikah.org/blender/curve_subframe_bug.png - > Red cubes are position markers showing where object *should* be each frame. - > Blue cube's location is animated by keyframes. It's interpolated correctly. - > Green cube is animated by the follow path constraint. It's drawn more ahead for every subframe. However, if you render whole frames or preview it through the timeline, it's shown correctly. That scene is rendered with full sample motion blur of 6 samples and shutter time of 3 frames. So from the code point of view, the last "blur sample" is rendered at full frame (scene->r.cfra) of 1, and subframe (scene->r.subframe) of 3.0. (This isn't isn't a bug in full sample motion blur calculation but in animation system. I originally run into this while testing Dynamic Paint subframes. :)%%%

Miika Hamalainen commented

2011-10-31 18:42:39 +01:00

Changed status to: 'Open'

Sergey Sharybin commented

2011-11-01 13:03:49 +01:00

%%%Joshua: old style motion blur is using subframe steps. Can you check if the new animation system correctly uses it?
Thanks!%%%

%%%Joshua: old style motion blur is using subframe steps. Can you check if the new animation system correctly uses it? Thanks!%%%

Joshua Leung commented

2011-11-03 12:14:44 +01:00

%%%For starters, this file is going about things in the wrong way.

If you're going to animate the constrained object moving along the path by animating it through the constraint, you should change it to "fixed position" and then animate the "offset factor" slider (0-1 value).
Otherwise, the object moving along the path should be done by animating the path's "evaluation time" property.

The "offset" value you've animated here actually acts like a user-controlled "time lag" on top of the curve evaluation time (+ subframe offset) if "fixed position" is disabled. %%%

%%%For starters, this file is going about things in the wrong way. - If you're going to animate the constrained object moving along the path by animating it through the constraint, you should change it to "fixed position" and then animate the "offset factor" slider (0-1 value). - Otherwise, the object moving along the path should be done by animating the path's "evaluation time" property. The "offset" value you've animated here actually acts like a user-controlled "time lag" on top of the curve evaluation time (+ subframe offset) if "fixed position" is disabled. %%%

Joshua Leung commented

2011-11-03 12:20:22 +01:00

%%%EDIT:
However, checking more carefully (i.e. even in case with animating "evaltime" directly), it seems that the problem here was actually applying the subframe offsets, instead of forgetting to apply them. This is because by the time the constraint gets the time, it has already had time offsets applied, but applying manually just compounded the problem!

So, fixed in svn!
%%%

%%%EDIT: However, checking more carefully (i.e. even in case with animating "evaltime" directly), it seems that the problem here was actually applying the subframe offsets, instead of forgetting to apply them. This is because by the time the constraint gets the time, it has already had time offsets applied, but applying manually just compounded the problem! So, fixed in svn! %%%

Joshua Leung commented

2011-11-03 12:20:22 +01:00

Changed status from 'Open' to: 'Resolved'

Joshua Leung closed this issue

2011-11-03 12:20:22 +01:00

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"Follow path" constraint subframes calculated incorrectly #29113