No, I have never provided extensive documentation. MCUFRIEND_kbv only does the hardware e.g. read_ID(), pushColors(), vertScroll(), ...
All the graphics come from Adafruit_GFX.h e.g. circles, lines, ...
All the text printing come from Print.h
You read the appropriate GFX docs and tutorials. Quite honestly, circles, triangles, ... are pretty intuitive from GFX. Things like setTextColor() or printing float expressions with different number of decimal places are not so obvious.
My approach is always to run all the examples from a library first. It gives me some idea about the capabilities. I can then adapt the example code to implement an individual sketch.
You don't have to read any library CPP code at all. Just the example INO sketches.
But mostly it is just running and observing the examples.
Yes, I tend to read the H files rather than tutorials when I want to see overloaded method arguments.
This Forum works quite well. You can quote library examples. You can explain what you want to do.
Several library authors give very good answers and suggestions e.g. olikraus for U8g2lib, bperrybap for hd44780, bodmer for TFT_eSPI, ...
Incidentally, your suggested animation requires software intervention with most TFT hardware.
Some OLED hardware can do it all by itself !
David.