Reposted by Shantanu
One of my most requested articles is something on inverse kinematics and foot sliding. I finally found the time to write up the little recipes that have served me well through the years, including an offline method I used recently that works surprisingly nicely.
theorangeduck.com/page/inverse...
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# What's a PRNG
Most random number generators that you see on computers are pseudorandom number generators.
These are algorithms that output random-looking numbers based on one or other form of initial seed or state. Same input means same outputs!
Typically each iteration the generator will modify its internal state and return a value.
For example, a tiny, pitiful implementation of Lehmer random number generator might look something like this:
newState = (oldState * 7) % 11;
Given an initial state/seed of 3, this would output
[...]](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:u3hek6kpzqeee3xa6f65otna/bafkreiafqnvmiytybquifjrskuxxzbb3qute7mdkeqq5pltuamgrjm2wb4)
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# "Save scumming"
[image: A person with a sword and a shield stands on an isometric tile and innocently looks at a "17%" label above them]
If your game involves chance actions and allows to save/load the game before performing such actions, players will inevitably figure out that they can save and re-load the game to re-try the roll until they get what they want.
GameMaker does not currently allow to save/load state of the built-in random generator (and likely won't in the near future), but with a custom generator, you could save its state along with the game and load it back so that performing the same action after loading the game will always yield the same result.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:u3hek6kpzqeee3xa6f65otna/bafkreic4qctlqnihdw5tbhuwzepdkkqcgkfgwyuq65lscczhwgigvd5lru)
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# WELL512
This is the PRNG that GameMaker itself uses!
Standing for Well Equidistributed Long-period Linear, it's a RNG with state consisting of an index and 16 unsigned 32-bit numbers. Allegedly it's all-around pretty good.
This is another one where the code almost works if you copy-pasted it:
[...]](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:u3hek6kpzqeee3xa6f65otna/bafkreiecn2gkz7nbp23i7txygfc2znind3voccl5xhp5vru5iusot57nvy)
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# MINSTD
This generator is much simpler so it manages to beat some of the extension calls even on VM:
[graphs]
And on YYC, a global version almost beats the C++ raw pointer version!
[graphs]
You can squeeze a little more performance out of it by turning the generator into a set of macros:
[graphs]
Here I'm also testing a script that modifies a self.state variable with a forceinline tag, but that is not as efficient as doing this during a GML build with a macro.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:u3hek6kpzqeee3xa6f65otna/bafkreidyvaooylvppfdahfvjnl23sjb5yzrgbzqidrwyjb75czn2kmb42i)
