[Bf-cycles] Motion Blur Implementation

Matthew Heimlich matt.heimlich at gmail.com
Mon Jun 10 20:39:40 CEST 2013


Gavin,

You may also want to poke around in the Appleseed Render source code, as if
I recall correctly they have a pretty modern approach to deformation blur,
and a very similar architecture to Cycles as a whole.


On Mon, Jun 10, 2013 at 2:33 PM, Gavin Howard <gavin.d.howard at gmail.com>wrote:

>      Hello all,
>
>      Brecht, thank you. I will get going on that patch. Stuart, if you
> don't think that's a good idea, let me know. Otherwise, I'll use that to
> focus my code exploration.
>
>      Nate, because of the nature of deformation motion blur, it will
> include curved blur. It has to. The reason is because most deformation is
> done by rotation. My current plan is to simply add multi-step export to the
> Cycles addon. (All you smart devs should yell at me if that's a bad idea.)
> I am also going to browse LuxRender's source code to see how they did it.
> Regardless, at the end of this summer, not only will Cycles have
> deformation motion blur, it will get multi-step export (steps will be
> specified by the user) and curved motion blur by side effect.
>
>      God Bless,
>      Gavin Howard
> On Jun 10, 2013 9:39 AM, "Nate Wiebe" <natewiebe13 at gmail.com> wrote:
>
>> Not entirely related, but will the scope of this GSOC cover curved motion
>> blur?
>>
>> -NateW
>>
>>
>> On Mon, Jun 10, 2013 at 11:29 AM, Brecht Van Lommel <
>> brechtvanlommel at pandora.be> wrote:
>>
>>> Yes Blender supports this, it does scene.frame_set(frame, 0.0) now,
>>> the second value is a subframe value between 0.0 and 1.0.
>>>
>>> On Mon, Jun 10, 2013 at 4:58 PM, Gavin Howard <gavin.d.howard at gmail.com>
>>> wrote:
>>> >      Hello,
>>> >
>>> >      Does Blender allow exporting at arbitrary subframes? If not, that
>>> might
>>> > be a problem. If so, then Stuart has me exploring the code, and I
>>> think that
>>> > I could write the patch while doing so. Does that sound okay?
>>> >
>>> >      God Bless,
>>> >      Gavin Howard
>>> >
>>> > On Jun 9, 2013 6:34 AM, "Brecht Van Lommel" <
>>> brechtvanlommel at pandora.be>
>>> > wrote:
>>> >>
>>> >> 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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