You must mean: what are tu and tv? _Asin is going to return an angle. The t of tu and tv my guess is: t is for translate because we are getting a point off the rectangular image and projecting it onto the sphere/circle in 2d. (Line 57 for me is x = x + 1 and I know you don't mean that!)
Translations are done like converting x, y coordinates to polar you need and angle and a distance from an origin.
I suspect tu and tv are getting the angles for the translation. Looking at pc using tv and tu we might be doing the reverse, translating polar to x, y coordinates?
Take the above as possible clues not gospel.
I believe this is first time I've ever seen _Asin practically used but I don't live the life of Pete
Update: Oh we are getting (x, y) points off the sphere/circle/disk and looking at the Point color on the Image for the color. Notice how the code is like our circle fill routines with x,y about cx, cy.
BTW we could use this for really fancy gradients unfortunately it would be pretty slow.
Translations are done like converting x, y coordinates to polar you need and angle and a distance from an origin.
I suspect tu and tv are getting the angles for the translation. Looking at pc using tv and tu we might be doing the reverse, translating polar to x, y coordinates?
Take the above as possible clues not gospel.
I believe this is first time I've ever seen _Asin practically used but I don't live the life of Pete
Update: Oh we are getting (x, y) points off the sphere/circle/disk and looking at the Point color on the Image for the color. Notice how the code is like our circle fill routines with x,y about cx, cy.
BTW we could use this for really fancy gradients unfortunately it would be pretty slow.
b = b + ...