I hope I'm not oversimplifying what a bone is, but using GMS terms wouldn't it be the equivalent of a fixed point with lengthdir_x/y being applied?
It's certainly possible to recreate what spriter does in GMS code, the only problem when using Studio itself is that it is very poor at sprite rotation - whether it's a textured primitive or a sprite it will have a lot of pixel distortion. Spriter is a lot more efficient in this regard!
To my mind (as an inexperienced programmer) you'd need to have an object with an x/y point to "build" your skeleton from: say you're doing an arm, then the object would be the "shoulder", and the arm would be -
shoulder.x + lengthdir_x (length,angle);
repeat for lengthdir_y etc.
That's if you're using using textured primitives, and are rotating the end around the "shoulder": if you were rotating a sprite then it's even simpler - set the x/y of the sprite to the x/y of "shoulder" and it will rotate around that point, that's your upper arm - the lower arm would be a point defined from the shoulder with lengthdir etc. 'Length' would simply be sprite_get_height (current sprite)
I know that this is possible as I have made my own equivalent in GML code, but as I said the end result isn't worth pursuing because GMS seems rubbish when using it's own sprite transformation code (or other) - you get an ugly pixelated mess!
