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Activator
01-10-2008, 12:40 AM
Hey all-

I just lost a project because I was unable to get one part of an effect that the director wanted. I'm curious as to how I might have achieved this elusive effect...

So, I had to do a VFX shot where a "Vampiress" was pulling back from the neck of another woman, and "sucking" blood from the "wound" (which was created with makeup in the live shot) as she pulled back (about 6 inches). There needed to be a steady, moving "stream" of blood going from the wound to the mouth of the Vampiress.

I was able to get an AWESOME stream of blood going from the wound to the mouth using TP and Metaballs. The blood also matched and filled in the makeup wound. The director was thrilled with this part of the effect, but he wanted more.

The part I could not get was the addition of "strings" of blood "pulling" at the wound and also attached to the lips of the Vampiress. These "strings" would need to break and spray blood as she pulled back from the wound.

I tried using splines to direct thin streams of particles, splines with sweepnurbs, and cloth effects (not something I'm too familiar with). No luck.

The biggest problem was that I needed to follow both the "wound", AND the mouth of the Vampiress. I hand keyframed the 2 movements, but I couldn't figure out a way to use the hand-tracked keyframes to control BOTH ends of a 2 point bezier spline! Cutting/pasting the keyframes didn't put the points in the correct places.

How can you paste 3D keyframes onto SINGLE point-animated spline points? And what would be the best way to create a "stringy bubblegum that you stepped on and it stuck to your shoe" effect?

Maybe a C4D Challenge is necessary? :-)
Per-Anders
01-10-2008, 02:47 AM
Try using the splines in the metaballs object directly, another optino would be to use cloth with tering and use a stringy like texture on the surface (perhaps with some noise mixed using the "Levr" overlay mode and driven by a vertexmap using the tension tag.
Activator
01-10-2008, 12:17 PM
Thanks Per. I didn't realize I can use a spline directly in a Metaball. That's cool!

I think the bigger issue, for me, was how to copy the tracking data (X,Y,Z axis) that I hand-tracked to a Null, onto ONE point of a spline, using Point Level Animation.

I could obviously have RE-tracked each spline point by hand, but the shot was 272 frames, and there would need to be a 1/2 dozen+ "strings", each tracked to a different part of the wound/mouth. If I could transfer the data from the tracked Nulls, and offset the spline points, it would save 2 days of hand tracking.
Sammer
01-10-2008, 12:45 PM
Hi Activator,

Assuming I understand the set-up correctly, you could pin a point of a spline to the tracking null with expresso. Or, if you have hair, you could have fixed either end to the mouth/wound and used spline dynamics.
ChrisCousins
01-10-2008, 01:07 PM
Or maybe IK-splines would be worth a look, you could constrain each end to your meshes and maybe use one handle mid-way to control the movement as the threads start to stretch, there would still be some hand key-framing in there but you have good control with a clean setup.
Creature
01-10-2008, 01:10 PM
Using XPresso really is the way to go here. Bring in your Null, add the position output to it and link that to the PointPosition input of a point node. That's it really. You just need to feed your spline to the point node and in the point nodes setting set the index of the first (or last) point of your spline.
JoelOtron
01-10-2008, 03:24 PM
I'm imagining the sort of growing tendril effect in Spiderman 3 (venom)?

Theres a free plugin called "spline on spline" which you can apply to your metaballed spline paths. The splines themselves can grow (draw your spline path, then spline on spline allows you to keyframe the length of the spline from o to 100).
Creature
01-10-2008, 03:33 PM
SplineOnSpline is available from www.aixsponza.com
JoelOtron
01-10-2008, 03:57 PM
Yeah thats it creature--thx.

Heres a QUICK test using spline on spline, 3 splines in a metaball. Theres issues with the "ball surface" along the length of the paths. Might be able to be hidden through displacement.

MOVIE (http://www.betatronstudios.com/joel/tendril.mov)
Sammer
01-10-2008, 09:30 PM
Failed to mention earlier that constraints (if you have them) would work pretty slick too.
ernia
01-10-2008, 10:17 PM
This would have been a fun little challenge.

Is this sort of what you were needing? Done in cloth and very basic, but the effect is there.

http://www.mplusxdesign.com/c4d/stringyblood.mov

ernia
Activator
01-10-2008, 10:31 PM
Wow- Some great ideas/solutions here! If I had had more time, I could have probably solved the issue... oh well. The director was the type who would probably NEVER be 100 satisfied, so I probably saved a few grey hairs!

Thanks for the Spline on Spline plugin link! The test JoelD did is great! The strings would need to be about 10 percent as thick, but I'm going to play around with Spline on Spline.

I should have guessed that I could use Xpresso to link the point to the tracked Null! Just showing my newbie-ness. C4D is so deep, I don't think I'll ever learn all the little tricks!

What about having the strings "break" as they stretch? I thought ClothFX would be the way to go, but I have zero experience with Cloth, and it seems that any effect needs pre-frames to "relax" before it'll work correctly.

Could a Cloth object be linked to a Spline that has it's Points locked (or have it's own points locked) to the 2 separate Nulls via Xpresso? AND still "tear"? Now THAT would get very close to the right effect if it were combined with some Particle streams, blobs and spray...
Activator
01-10-2008, 10:34 PM
ernia-

Hey, that's pretty good! It would need to be "stringy-er", and the tear would have to happen during a smooth separation of the two ends, but that's a great start!

Going to go play now!
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