Since I am majorly late to respond to that particular post and my contribution would likely be entirely unhelpful at this point, I thought I'd just draw one and post it in a separate post.
To be as fully unhelpful to the BYOND community as I can, I have done it in a western comic art style, although that's partly to also make it easier for people to see where the shadows are, so maybe I win back some helpfulness points for that.
I am using a total of 6 colours (including the background) and the image size is 32x32.
4x zoom version so you can see what the sitch is.
Main shadow areas are;
On the arms where they are facing toward the floor (before bending upward at the elbow joint).
I was originally going to make it all shadow but then later decided to do a 2x2 block of the next darkest blue to indicate biceps, this breaks the style a bit but I think it's passable.
Under the neck between his collar bone and his bulging trap muscles.
In a situation where 2 objects are close together and cause a crevice/pit where light runs out of bounces to reach is referred to as an Occlusion shadow, these are like cast shadows that require a bit more teamwork to exist.
I also put the occlusion in between the top of his pecks since his head's cast shadow has darkened the area already. This also frames the face quite well from a composition stand point, so it's always nice when things conveniently pull together to improve the focal point.
Under his ribs and his vortex whirlpool legs.
Normal legs aren't so bad since its usually the lower you get, the darker the general tone is and it gives that impression of downward depth (although the tops of the feet would need to be lighter since they would be more parallel to the light source).
However, with a vortex it isn't just getting lower, it's also gaining surface area the lower you get, meaning more parts of it will be getting hit by light.
For this you just have to try and fill in a twirl shape with dark occlusion shadow since it will fold inward at the parts where the water overlaps.
Lit up areas will be right beneath the occlusion shadows since that would be the waters highest and therefore flattest area (as it is the transition point where it goes from one steep drop to the other).
Well, I hope this helps people in some way and thank you for reading.
