Blender Git Loki

Motion blur investigation feature

This commit adds a way to debug Cycles motion blur issues which
are usually happening due to something crazy happening in between
of frames. Biggest trouble was that artists had no clue about
what's happening in subframes before they render. This is at
least inefficient workflow when dealing with motion blur shots
with complex animation.

Now there is an option in Time Line Editor which could be found
in View -> Show Subframe. This option will expose current frame
with it's subframe to the time line editor header and it'll allow
scrubbing with a subframe precision in time line editor.

Please note that none of the tools in Blender are aware of
subframe, so they'll likely be using current integer frame still.

This is something we don't consider a bug for now, the whole
purpose for now is to give a tool for investigation. Eventually
we'll likely tweak all tools to be aware of subframe.

Hopefully now we can finish the movie here in the studio..