[Bf-cycles] Motion Blur Implementation

[Brecht Van Lommel]

We should support exporting at the exact shutter time. At the time I
implemented motion blur evaluation at subframes was actually broken
for shape keys and physics systems so I didn't use it, but that has
been fixed since.

However, exporting motion from the frame positions may be useful to
keep as it may give more predictable results in some cases. When
you're editing animations that's the only thing you actually see in
animation playback, so the motion between those frames may contain
some unexpected things that you don't want to render.

I don't know how common that is, did not look at .blend files yet to
see how different the results are, if it is an issue we should
probably have an option (off by default) to only export motion from
integer frame numbers and no subframes.

On Sat, Jun 8, 2013 at 7:36 PM, Gavin Howard <gavin.d.howard at gmail.com> wrote:
>      Hello all,
>
>      I have a question about implementation. I have been told by
> Brecht that currently, the Cycles addon exports three steps for motion
> blur to the renderer: one at the previous frame, one at the current
> frame, and one at the next frame.
>
>      Now, my memory may not be serving me well here, so I may have
> gotten the details wrong. But if not, shouldn't the addon actually use
> the shutter time to determine the first and third steps? For example,
> shouldn't the addon export a step at the start of the shutter time,
> one at the current frame, and one at the end of the shutter time?
> Also, I think this type of reasoning should apply even when multi-step
> (more than 3) motion blur is added. (Multi-step blur is needed for my
> Deformation Motion Blur GSoC project, so I will add it over the
> summer.)
>
>      In short, I think that the shutter time should be the goto for
> exporting motion blur steps. If it is, then just ignore this. But if
> it's not, should we change it? Anyway, that's my two cents.
>
>      God Bless,
>      Gavin Howard
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