[Bf-blender-npr] Feature/improvement idea for Freestyle

[Tamito KAJIYAMA]

Hi Terry,

I have seen many cases too where lines suddenly showing up and
disappearing are distracting, so I see the point of your post.

Concerning crease lines, they are independent of the view point (that
is, they are detected regardless of the camera setting). If objects are
not deformed, then crease lines are stable (i.e., they are always
there). If this kind of stable crease lines undergo sudden vanishing or
appearance, that is likely a bug (please, report it).

Changing the thickness of a crease line depending on the angle between
the two faces on both sides of the line is technically possible. I just
did a proof-of-concept implementation using the Python Scripting mode of
Freestyle in Blender. See https://vimeo.com/91306354 for a quick test
result. Implementing this crease angle dependent line thickness in the
Parameter Editor mode needs further coding (that could be a short term
goal).

Contours, on the other hand, are view dependent lines. Varying contour
line thickness along with camera movement is technically challenging,
because we need to track contour lines from frame to frame. Maintaining
inter-frame properties of lines (such as stability and gradually varying
thickness) is a problem called temporal coherence. Freestyle does not
address it at all. Stéphane Grabli, the primary author of the original
Freestyle program, said in an interview (*) that "this is a difficult
problem which might be best avoided". For now it is unlikely that the
temporal coherence problem is solved in Freestyle for Blender.

* 
http://libregraphicsworld.org/blog/entry/freestyle-jot-and-the-future-of-non-photorealistic-rendering

Best regards,

-- 
KAJIYAMA, Tamito <rd6t-kjym at asahi-net.or.jp>


On 07/04/2014 14:36, Terry Hancock wrote:
> Hi all,
>
> I was just looking at a Freestyle animation which had a problem I've
> encountered myself. Sometimes you need to have a crease or contour line, but
> as the camera angle changes, it will just disappear.
>
> Apart from whether it looks better with or without the line, the sudden
> vanishing or appearance creates a distraction in the animation flow. It'd be
> nice to have a way to make such changes more gradual.
>
> One way would be to fuzzify the rules for the edge classification -- with the
> "crease" line, I suppose this means turning the "crease angle" value into a
> range.
>
> But, as the 'suggestive contour' is supposed to be "close" to a contour line,
> it would make sense if one could specify "how close", and again have that be
> "fuzzy".
>
> The fuzziness could then be input for a line style modifier --- and then you
> could use it to allow an alpha-fadeout or a thinning of the line, rather than
> having it suddenly disappear.
>
> Cheers,
> Terry