Retera Model Studio is bugged in this case and I did not expend the software development time to fix it.
If we animate movement from {X1, Y1, Z1} to {X2, Y2, Z2} on a computer, such as from {0, 0, 0} to {100, 100, 100}, we store those as two points to travel to and then if we have a 2.0 second animation the computer generates the movement between these. So if you are 0.5 seconds into the animation, the object can be located at {25, 25, 25}. If you are 1.5 seconds into the animation, the object can be located at {75, 75, 75}.
If we do the math this is linear interpolation. Any position can be computed by multiplying the difference between the two points against time.
But Warcraft III was built to have prettier animations than this. Instead of linear motion from here to there, a more complex curve equation is used. If you want to look this up online, actually, every model can choose either Linear, Hermite, or Bezier as their curve equation. But if the model is Hermite or Bezier, in order for the math to work, we must embed the outward tangent from the starting point, and the inward tangent from the ending point.
If we make the MDX model file using the War3ArtTools from Blizzard, which are a 3DS Max 4.9 plugin from the year 2003, the tools back then were smart enough to automatically create inward and outward tangent data, to make very smooth motion.
If we make the MDX model using the Reforged art tools that were accidentally published (since Reforged doesn't directly support custom models in the same way Warcraft III did), we can see that they generally make all animations Linear so that their devs in a hurry don't have to deal with this problem.
But if we make an MDX model in Retera Model Studio, at the moment if a bone is in Hermite or Bezier mode, when we make new animations my code injects in the outward tangent and inward tangent by copying the actual start and end value which is mathematically incorrect.
If you use Edit > Optimize > Linearize Animations then all animations of all bones change to Linear, and we erase all inward and outward tangent data. Once you do that, the data is erased and you can't bring it back, but then you wouldn't have the Hermite/Bezier curve math issues in the Retera Model Studio code.
NOTE: The only "wrong" tangents are the ones in newly created Hermite/Bezier animations in Retera Model Studio where you author new keyframes that did not previously exist. Prior existing animations have their inward/outward tangents preserved by Retera Model Studio. Meanwhile, this "Linearize" function erases all tangents, regardless of whether they were created in Retera Model Studio or from the original model.
