mcc, 1 month ago

I thiiiiink it's going to be equivalent to rotating by some multiple of 45 degrees and then scaling by a factor of sqrt(2)… I think. Doing the math as we speak.

WAHa_06x36, 1 month ago

@mcc That sounds correct. Possibly a mirror in there as well.

emilvolk, 1 month ago

@mcc maybe I’ve misunderstood the notational convention, but this looks like a transformation into the null vector?

mcc, 1 month ago

@emilvolk Sorry, it's uh, literally Rust. so in python it would be like saying

x2 = x + y
y2 = x - y

emilvolk, 1 month ago

@mcc ironically enough I know rust better than python. In any case, y = 0, and 2y = x, so you still get a null vector. This makes sense because the vectors are linearly dependent.

mcc, 1 month ago

@emilvolk The assignments happen simultaneously; all values on the right side are equal to the values before the assignment.

exa, 1 month ago

@mcc tbh I always draw a big "1" and transform the 3 points just to be sure.

mcc, 1 month ago

@exa That is a good idea. I am currently for similar reasons transforming the square where [0,1] on the x axis corresponds to [0,1] on the red channel and [0,1] on the y axis corresponds to [0,1] on the green channel, but that's clearer.

exa, 1 month ago

@mcc yap might work too. But linear algebra on colors confuses me too much. :D

Wikisteff, 1 month ago

@mcc That's a weird one. Do you mean (x', y') = (x - y, x + y), rotation by 45°, followed by a scale by sqrt(2)?

[x'] = [1 -1] [x]
[y'] [1 1] [y]

That is rotate by 90°, followed by a mirror about the line y = x, and a scale by sqrt(2), unless I got it wrong somehow.

not2b, 1 month ago

@mcc It is a 2 by 2 matrix. You can express that matrix as a combination of a translation, a scaling, and a rotation.

mcc, 1 month ago

@not2b This is an accurate description of a 2D affine transformation but does not get me closer to knowing which 2D affine transformation this is (I think I figured it out tho)