Spooky Scary Skeletons

Well if you haven't yet figured out the topic of today's blog then then you should get your brainbox checked. The topic of today's blog is skeletons! And by skeletons I mean the kind that you form inside of a 3D model in order to dictate the manipulation of the mesh and not the kind that keeps your body from looking like a pile of squishy, saggy, meat-flesh.

This is what happens when Frankenstein has too much fun with silly putty

Skeletal animation is currently the most popular technique used in animating movable objects in a game, at least when it comes to organic objects such as people, animals, and other creatures. Skeletal animation consists of 2 main components: the mesh, and the skeleton.

The mesh or model is a connected conglomeration of polygons that that make up the shape or body of the object to be animated. So if the object to be animated is a horse then the mesh would be in the shape of a horse.

The skeleton is a series of joints ordered in a hierarchy, positioned in the places where the object is supposed to bend or deform.

why is it that videogame babies usually look creepy instead of cute?

Even though there are shapes, called bones, connecting joints; these bones do not effect the animation of the character.Only the joints are taken into account when animating, bones are simply there to help the animator see the shape and hierarchy of the skeleton.

When the skeleton and the mesh are created and put in their proper positions, in other words the skeleton is placed correctly inside the mesh. The mesh is "skinned" to the skeleton. This means that the vertices of the mesh are bound to the joints of the skeleton so that when the orientation and position of the joints changes, it effects the position of the vertices. The amount of effect a joint has on a vertex, more commonly known as weight, can be changed so as to give the mesh a more desirable deformation as the skeleton is manipulated. It is very easy to have skin weights that create bad deformations so be vigilant.

That looks like it hurts

As mentioned before, only the vertices of the mesh are manipulated by the skeleton. Ultimately this is done to reduce the amount of date needed to make these animations happen. Now in an ideal world where we are able to do anything, at any time,  anywhere, the most perfect animation system would essentially be your body. Your body is made up of cells which in tern are made up of molecules, which can be broken down into atoms, which can be broken in subatomic particles which can be broken down into strings? or is it waves? I have no idea. The point I am trying to get at is that when you move you body each of those cells, molecules, atoms, etc. moves too. This can be though of as the ideal animation system, where we have objects made up of hundreds of thousands of points which make up the object and each of them being manipulated. Can you imagine the sheer MAGNITUDE of the amount of data required to do anything of that scale? UGH This is why the only the vertices are used, to save data.

Save data

If you were to use morph targets as well the amount of data used is even less because you are now restricting the degrees of movement to a discrete set of movements as oppose to allowing the object to be able to move all over the place.

Sources

Gregory, Jason.Game Engine Architecture. Boca Raton: CRC Press, 2009.

Soriano, Marc. "Skeletal Animation". Bourns College of Engineering. Retrieved November 2013.

Owen, Scott (march 1999). "A Practical Approach to Motion Capture: Acclaim's optical motion capture system: Skeletal Animation". Siggraph. Retrieval November 2013.

http://www.youtube.com/watch?v=K2rwxs1gH9w

http://files.coloribus.com/files/adsarchive/part_1400/14009805/biovision-blob-fish-600-69817.jpg

http://upload.wikimedia.org/wikipedia/commons/a/ab/Skeletal_animation_using_Blender_software.png

http://wiki.blender.org/uploads/thumb/e/e6/RST.65.png/600px-RST.65.png

http://images2.fanpop.com/image/photos/9400000/Lt-Commander-Data-star-trek-the-next-generation-9406565-1694-2560.jpg

https://www.youtube.com/watch?v=iRZ2Sh5-XuM