Rotating a 2D array using matrix transformation

Asked Dec 14 '14 at 05:24

Active Dec 14 '14 at 05:24

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I am writing a program that needs a nxn array to be rotated about it's center. Rotations are only at 90-degree angles.

What I do is I translate the origin to the center and perform the rotation, then translate it back again.

For example,a 3x3 array:

0 0 1
0 1 1
0 1 1

when rotated 90 degrees about it's center, becomes:

1 1 1
0 1 1
0 0 0

using (1,1) as it's center, then after getting the positions relative to the center, applying the rotation transformation. The problem is when I have an even-numbered dimension, a 4x4 array for example:

What is it's center? Or rather, how do I correctly rotate the array using a transformation matrix?

Edit: assume that the arrays can contain anything, integers or maybe even objects

asked Dec 14 '14 at 05:24

userx01

If these are truly matrices, why can't you use the transpose operator? – apnorton Dec 14 '14 at 05:30
well, actually, I don't want this to be language-specific, and as efficient as possible – userx01 Dec 14 '14 at 05:51
it doesn't need to be a matrix, but what I'm trying to do is to rotate objects in a grid – userx01 Dec 14 '14 at 05:56
1

possible duplicate of [How do you rotate a two dimensional array?](http://stackoverflow.com/questions/42519/how-do-you-rotate-a-two-dimensional-array) – apnorton Dec 14 '14 at 05:57
Specifically, [this answer](http://stackoverflow.com/a/20199933/2390644) shows conceptually what's going on. – William Price Dec 14 '14 at 23:41

Rotating a 2D array using matrix transformation

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