Well it really depends on what you think the gist is. The question can be interpreted in 2 ways.
- What is the syntax of expressions and how to expression nodes work?- How do you know whet the expression is for a given problem?Well it turns out that the first one is easy to answer, it takes less than a page to learn. Off course if the reader can NOT provide the second questions answer themselves then knowing the former is of no use. Because the first question is relatively easy that's all people usually answer. Same problem arises with scripting.
The real problem is the second question and this is what I define as the 'gist of it' as you so succinctly phrase the question. Well this is a very broad subject of discussion, no single book will be able to tackle this problem. Its the rot of thing thst comes form ALL your other education, you know this is where you use all those things in school you were so adamant you'd never need. So this part encompasses everything you know but mainly i have found following useful:
- Math, to name a few subjects among math that i find highly useful: Geometry, trigonometry, vector math, linear algebra, calculus, numeric methods (Rudge-Kutta and Newton iteration, Monte Carlo method!), interpolations
- Physics (as the primary form of applied math) mostly i find that engineering dynamics is of high value because they discuss on how the functions get derived, optics, acoustics and kinematics
- Computer science for understanding algorithmic complexity
- Computer engineering is slightly useful for adapting this knowledge into a easily computable form
- Signal theory, especially control systems and feedback loops
- Simulation Modeling
- Engineering Philosophy, especially parts on dealing with how to find solutions to problems you don't know how to solve
- Animation theory
- Music
- Photography
- Informatics
- Storytelling
- Choreography and timing
- ...
So basically everything I know. So the 'gist of it' is that expressions really are some kind of glue between what you know and happen to want to use and rest of maya. The real deal is if we would know all the expressions you would need we would do them for you, but seeing as we can not enumerate them all then the onus on solving the problem falls on you. So if you learn this form a book then your doing it wrong, because its not about reading a book but using everything you ever read. So no i dont see any book that could teach it all. But i can recommend about 100,000 pages worth of reading tough.
But broadly speaking there's 3 categories of problems:
- simple ones you already know how to solve
- ones thet you need to make a function for
- and ones that have functions that are affected their own control state (these are hard since we don't know how to solve them). The rotate wheel problem falls into this category, and they are usually not solvable without some sacrafices to the way you work.
problems in 1 are hard to quantify because i dont know what you know. But presumably you can solve problems like midpoint of line, how many cars there is on a lot with 32 wehicles and 98 wheels, if the distance between 2 measurements is 10 meters and the paralax is 2 degrees how afer away is a object, you drop a ball from 10 meters height how long before it hits the ground etc. the kind of stuff you were taught in primary school.
Problems number 2 are usually just searches in the lore of science, if not they will involve either some fitting, intuition, measurement or integration. Example of problem like this is, shoot an arrow where does it land and how does it fly, how would a ball bounce on flat floor given a initial velocity, the function of a spring finding equilibrium, how much does a object grow in other dimensions when squeezed in one and so on.
problems number 3 are most interesting, they and problems in 2 also (but not recommended) can usually be solved by discretisizing the problem up into small linear pieces, or into iterations/montecarlo methods. Good ones are how to simulate momentum in a antenna of a alien, how does a flag wave, how to simulate a rope tying up and so on.
Now i dont currently have a maya in front of me to write examples of each category (because they need testing to make sure my expressions work).
but they're all small examples.
Thats because thets all you would use really.