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Nice, I was just reading how to solve the same problem using geometric algebra: https://www.jeremyong.com/klein/case_studies/ga_skeletal_animation/ https://www.

by wrnr 6y ago

Nice, I was just reading how to solve the same problem using geometric algebra: https://www.jeremyong.com/klein/case_studies/ga_skeletal_animation/ https://www.jeremyong.com/klein/case_studies/ga_skeletal_ani...

lasagnaphil 6y ago
Although it says that it's solving the problem using geometric algebra, I really can't see how GA makes the problem easier (in terms of both conceptual simplicity or implementation). You can replace the term 'motor' in the article with 'dual quaternions' and the whole thing doesn't get any more simple or complex.
gfxgirl 6y ago
unfortunately, IIUC, GA doesn't handle scaling. It's ironic the picture of a T-POSE in that article is a cartoon like character. Cartoon animation is full of "squash and stretch" which means lots of animation of scale.
- AnthonBerg 6y ago
  I’m still only circling geometric algebra – could you give me some leads on GA not handling scaling? I’ve understood it such that it did, but I’d love to dig into it however it is :) Thanks!
  - amelius 6y ago
    You probably want projective geometric algebra. http://projectivegeometricalgebra.org/ http://projectivegeometricalgebra.org/
    - AnthonBerg 6y ago
      Perfect! Thank you so much!
  - DonHopkins 6y ago
    You should try triangulating geometric algebra too! ;)
    - AnthonBerg 6y ago
      :kiss: MWAH :heart:
- bsenftner 6y ago
  Squash and stretch is not implemented with scaling. In fact, for any rational animation system (meaning one that a non-engineer digital artist can actually use) the use of scaling is simply not available in the system. Scaling in a hierarchical animation system is a guaranteed method to fuck up an untold large number of additional systems such as the physics/dynamics associated with the scaled character as well as any geometry attached to the character, as well as any sub-systems which use the now-scaled character for decision triggers. There are simply too many inter-dependent systems that rely on aspects of the environment, such as the scale of objects, to remain consistent for the entire illusion of a consistent world to be maintained. Speaking from experience: I've written dozens of 3D animation systems for games and film VFX. I've been writing 3D animation systems since the 80's.
  - gfxgirl 6y ago
    So have I. I can assure you there is scaling in every game and VFX I've worked on since the late 90s
    - bsenftner 6y ago
      You may have scaling in your tools, but under the hood the transformation pipeline treats the result as a translation. Scales cause physics and dynamics issues, which are linked to too many related systems. That's why tools that scale have a "bake" operation afterwards, that baking is transforming scales into translations so runtime and scene logic can use a uniform coordinate space.
      - gfxgirl 6y ago
        Not my experience. Have shipped several AAA games with scaling, no baking.

by wrnr 6y ago

lasagnaphil 6y ago

Although it says that it's solving the problem using geometric algebra, I really can't see how GA makes the problem easier (in terms of both conceptual simplicity or implementation). You can replace the term 'motor' in the article with 'dual quaternions' and the whole thing doesn't get any more simple or complex.

gfxgirl 6y ago

unfortunately, IIUC, GA doesn't handle scaling. It's ironic the picture of a T-POSE in that article is a cartoon like character. Cartoon animation is full of "squash and stretch" which means lots of animation of scale.

AnthonBerg 6y ago
I’m still only circling geometric algebra – could you give me some leads on GA not handling scaling? I’ve understood it such that it did, but I’d love to dig into it however it is :) Thanks!
- amelius 6y ago
  You probably want projective geometric algebra. http://projectivegeometricalgebra.org/ http://projectivegeometricalgebra.org/
  - AnthonBerg 6y ago
    Perfect! Thank you so much!
- DonHopkins 6y ago
  You should try triangulating geometric algebra too! ;)
  - AnthonBerg 6y ago
    :kiss: MWAH :heart:
bsenftner 6y ago
Squash and stretch is not implemented with scaling. In fact, for any rational animation system (meaning one that a non-engineer digital artist can actually use) the use of scaling is simply not available in the system. Scaling in a hierarchical animation system is a guaranteed method to fuck up an untold large number of additional systems such as the physics/dynamics associated with the scaled character as well as any geometry attached to the character, as well as any sub-systems which use the now-scaled character for decision triggers. There are simply too many inter-dependent systems that rely on aspects of the environment, such as the scale of objects, to remain consistent for the entire illusion of a consistent world to be maintained. Speaking from experience: I've written dozens of 3D animation systems for games and film VFX. I've been writing 3D animation systems since the 80's.
- gfxgirl 6y ago
  So have I. I can assure you there is scaling in every game and VFX I've worked on since the late 90s
  - bsenftner 6y ago
    You may have scaling in your tools, but under the hood the transformation pipeline treats the result as a translation. Scales cause physics and dynamics issues, which are linked to too many related systems. That's why tools that scale have a "bake" operation afterwards, that baking is transforming scales into translations so runtime and scene logic can use a uniform coordinate space.
    - gfxgirl 6y ago
      Not my experience. Have shipped several AAA games with scaling, no baking.