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I always wanted to know how physics and kinematics came together and could be worked on with code. Your blog post was enlightening. Thanks.
Such beautiful animations. Too much detail is missing from this post and its related post on "two-joint inverse kinematics" (that is actually three joint inverse kinematics) - what are the joint types? which inverse kinematics problem is being solved (position, orientation, or both?). This could be a great post if the author spends some more time polishing it.
I was recently wondering why foot sliding is still a common problem in fighting games. Surely with Inverse Kinematics it should be possible to fix this problem by now. I have the suspicion that people who are accustomed to fighting games are so used to it that they don't notice it anymore, or view it as correct behavior.
Is it really a problem? Game mechanics and physics are not always meant or desired to be realistic.
It's a graphical problem. Inverse kinematics is purely a graphical technique. It has no effect on gameplay. That doesn't mean it's irrelevant.
I imagine, that unsolved foot sliding is considered as a genuine part of the genre, but personally I really enjoy fixed feet in gameplay very much.
I would rate anything that is a sufficiently immersion-challenging distraction to be a problem.

Would the game be more fun if we just chop off all the character's legs and make them float like apparitions instead? That needn't actually change the nuts and bolts game mechanics, but it would be less realistic and/or require big story changes like "it turns out all these characters are ghosts" or something. Same with having every character float through walls instead of walk to a door to enter/exit so that we can save on pathfinding logic.

People are very accustomed to seeing other footed beings have their feet "locked" to the ground by the weight of their body as they stand, walk, or run. Having every character constantly look as though they are suspended by the waist with legs just dangling arbitrarily is something a lot of people are going to find immersion-breaking: and it's one of those issues where the more realistic detail you have in other areas the bigger this remaining issue stands out. Minecraft/Roblox/stick figure characters can probably get away with a lot less care on this detail than TF2-or-above realistic characters can.

This is a really great presentation
This is one of the best references on this topic I've seen - run cycles and foot locking are annoyingly lacking in documentation outside a few papers.
I'm currently spending all my hobby project tokens getting astro to help with this problem... but with skis on. Mind blowingly abysmal results so far! Thanks for showing your work.
Wow, after a lot of code, the animations at the bottom of the article are really mind-blowing. Super well done.
I really want to read this article but the videos keep hijacking the screen (on mobile web)

FYI in case the author sees this

Are you using Firefox on ios? It’s a long-running bug with that browser that affects most pages with multiple videos and drives me mad.
Auto tagging the foot contact points is kinda fun. I usually just see it hand marked in the source anim.