[SOLVED] How rotate mesh vertices?

[boruok]

Anyone here is familiar with behind quad rotation math? Trying to rotate specific quad in mesh, but can’t understand math behind it.

--[[
	       0-1-2  0-2-3
	3---2      2  3---2
	|2 /|     /|  |2 /
	|/ 1|    /1|  |/
	0---1  0---1  0
--]]

-- first
stream[offset + 01], stream[offset + 02], stream[offset + 03] = x,   y,   z
stream[offset + 04], stream[offset + 05], stream[offset + 06] = x+w, y,   z
stream[offset + 07], stream[offset + 08], stream[offset + 09] = x+w, y+h, z
-- second
stream[offset + 10], stream[offset + 11], stream[offset + 12] = x,   y,   z
stream[offset + 13], stream[offset + 14], stream[offset + 15] = x+w, y+h, z
stream[offset + 16], stream[offset + 17], stream[offset + 18] = x,   y+h, z

If you look image some quads are rotated toward right side…

because atlas generator decided to rotate image within atlas…

[horifiedbyeverything]

what rotation are you trying to accomplish exactly

[boruok]

what rotation are you trying to accomplish exactly

unrotate

[horifiedbyeverything]

so, the atlas somehow rotated the sprite a right quarter turn…

why can’t you rotate the sprite in the atlas?

[boruok]

why can’t you rotate the sprite in the atlas?

do you know how rotate image in atlas?

[boruok]

*TES: Oblivion music plays in background

[boruok]

I just bruteforced values…

if is_rotated then
	stream[offset + 01], stream[offset + 02], stream[offset + 03] = x+w, y,   z
	stream[offset + 04], stream[offset + 05], stream[offset + 06] = x+w, y+h, z
	stream[offset + 07], stream[offset + 08], stream[offset + 09] = x,   y+h, z
	---
	stream[offset + 10], stream[offset + 11], stream[offset + 12] = x+w, y,   z
	stream[offset + 13], stream[offset + 14], stream[offset + 15] = x,   y+h, z
	stream[offset + 16], stream[offset + 17], stream[offset + 18] = x,   y,   z
else
	stream[offset + 01], stream[offset + 02], stream[offset + 03] = x,   y,   z
	stream[offset + 04], stream[offset + 05], stream[offset + 06] = x+w, y,   z
	stream[offset + 07], stream[offset + 08], stream[offset + 09] = x+w, y+h, z
	--
	stream[offset + 10], stream[offset + 11], stream[offset + 12] = x,   y,   z
	stream[offset + 13], stream[offset + 14], stream[offset + 15] = x+w, y+h, z
	stream[offset + 16], stream[offset + 17], stream[offset + 18] = x,   y+h, z
end

[Mathias_Westerdahl]

That is valid way of doing it.

Another would be to use a decomposed 2D matrix as the restrictions make it quite simple:
E.g. like so (x, y) -> (y, -x)
Here’s our code for that defold/engine/gamesys/src/gamesys/components/comp_sprite.cpp at dev · defold/defold · GitHub