Stuff from the animation chapter.
12:00 - He's going to show braids, long hair, and how to make things not clip into each other.
13:30 - Not doing anything to the braid, it's stiff like wax were applied to it. Pretty easy to see.
14:20 - From top: Make the model and skin it [translator: I guess this means texture it]. Move the joints placed in the hair. (Green) Position before [translator: at -1 frame]. (Blue) Speed, gravity, forces which cause the joints to move back to their original position, etc. (Green) Position after [translator: current frame]. All this just means: every joint in Yayoi's braid here has some amount of tendency to go back to its original position, and is acted on by various forces like their current momentum and gravity (the returning forces mentioned before is actually one of these). Combine all these forces, and you've got your new position for one of these joints. These joints also have other properties to them, like facing (for twisting the hair), but these are ignored for now.
15:50 - (Top) Speed times some resistance (attenuation) factor. (Top green) The joints move by inertia, but speed eventually slows down naturally [literally: speed decays]. (Bottom green) Apply some resistance factor to speed when calculating joint position. Naturally, there must be some constraints to this, since if a joint moves on its own, it might move further away from the next (or previous) joint in the braid, then the braid becomes longer.
16:50 - (Top) The length between joints cannot change, and the base of the braid cannot move. (Bottom) The entire braid is pulled by the movement of the base.
17:50 ~ 20:10 - So, just applying speed and its decay... well, you get it. They put gravity and wind in, and... the feeling of volume is missing. So, they put in some more joints. These joints pull on the braid, though they don't actually fall on the braid (in fact, they're just points in space), and pull it back to its original position. With everything in place, Yayoi's twin tails animate quite well.
21:30 - Just a review of all the points above. (Top) Speed and speed abatement, gravity and wind, braids returning to their original shape. After all these are done, the length between joints is always adjusted to its original length. (Bottom) The important variables are: Speed decay factor, gravity, and the force factor for returning the hair to its original shape. (Bottom right) Tails all done!
22:00 ~ 24:20 - Moving on to long hair! First, hair has many lines of joints. The first movie shown has less than the second, I think. They put have spring forces between joints, to keep them from flying apart from each other. Essentially, you can think of them as a spring: if the connected points get too far apart (here, look at the red lines), they pull each other together, and if they get to close, they push each other apart.
26:10 - (Green) Long hair's done! (Bottom) Even if we're calling it done just by how it moves...
26:30 - Collision with swaying objects. (Top) Hair and skirts bump against the body and legs. (Middle left) Swaying objects use spheres. (Middle right) The body uses cylinders and spheres. For collision detection, a triangle-by-triangle test is incredibly ineffective, so usually they logically bound (encase) sections of the body with a combination of near-form-fitting primitives... simple things like spheres, cylinders, or boxes. These are the objects used for collision, not the actual triangles on the model, which makes it much faster. Note Mami's neck: there's a sphere here containing empty air, but regardless, if something hits the edge of that air, then it's considered to have hit Mami, in which case it bounces off or Mami goes flying.
27:20 - A list of all the types of objects used in collision detection. (Top) A plane, for floors and such. (Middle) Donut ring, for skirt edges and such. (Bottom) Tubes, for tail-like hair and such. Notice each of these is a bunch of objects roughly in the aforementioned shape (a tube can be a combination of spheres and cylinders).
27:40 - From top: How are spheres and cylinders used for collision. Cylinders are used for the body, arms, and legs. Spheres are used for joints. Swaying objects are usually just spheres. He shows these bounding volumes starting from the cylinders, going to the joints, then adding in all the swaying stuff.
29:10 - They couldn't show Iori for some reason, so we get Haruka and Takane. Notice the big cylinder behind Takane: this is there to keep her hair back.
Final slides.
31:20 - (Top) More fluid behavior (in animation).
31:25 - (Top) Additions and removals in flexibility. (Middle) Accessories didn't move around in L4U! (Bottom) Accessories sway around properly in Im@s2.
31:45 - Faster.
32:20 - From top: How swaying objects are processed in Im@s2. Simple movements, simple collisions, still with some great visual expression.
... And that's it. That took quite a bit. Personal opinions to come.
And the programmer, Maezawa Keiichi, would like everyone to remember Sensitive Tooning.
