The Arnold and OSL matrix is a 4x4 matrix.
You read it like a book, from left to right.
You can interpritate it as 4 vec4 structs.
RGBA
RGBA
RGBA
RGBA
Although they are infact just floats all together sitting on a string.
If you read downwards its
X
Y
Z
W
So typical rotation would look something like...
matrix ( cos(a), sin(a), 0, 0,
-sin(a), cos(a), 0 ,0,
0,0,0,0,
0,0,0,0);
So you just fill in the 2 first slots in the first to lines so to speak.
And you use the 2 math nodes cos and sin for the float value you are going to use as the driver for spinning it around on the U and V space. Dont forget to add a negative node for the second sin function.
With cos and sin you level out the fact that we sample a point on a circle which has exponential factors attached to it as we get closer to either 0 or 1 on both axis. And so the result will then be that if you pipe a linear increasing float value through "a" the rotation will be steady and linear.
Now you can spin it around any axis you want.
