How to rotate a 4x4 matrix (C#/XNA)

Question

I've got an array of [4,4]
X is the only one I "know", the rest is calculated with a simple double for-loop.

x 0 0 0
0 0 1 0
0 1 1 0
0 1 0 0

I want a function that take this array, and rotate it 90 degrees + / - while the position of x stays the same. (It's supposed to be tetris)

x 0 0 0
1 1 0 0
0 1 1 0
0 0 0 0

I know some way to hardcode the permutations but what that wouldn't learn me anything and it's frankly quite boring.

Would appreciate the help :>

Answer 1

I'm not sure how exactly you intend to rotate a matrix by 90 degrees and yet still have the top left X in the top left of the rotated version, but to rotate something by 90 degrees, I'd just make a new array, swap rows and columns and flip horisontally.

int[][] start = new int[4][];
start[0] = new int[4] { x, 0, 0, 0 }
start[1] = new int[4] { 0, 0, 1, 0 }
start[2] = new int[4] { 0, 1, 1, 0 }
start[3] = new int[4] { 0, 1, 0, 0 }

int[][] rotate = new int[4][];
for (int i=0; i<4; i++) rotate[i] = new int[4];
for (int i=0; i<4; i++)
    for (int j=0; j<4; j++)
        rotate[i][j] = start[j][i];

Rotate finishes with:

0, 0, 0, 0,
0, 0, 1, 1,
0, 1, 1, 0,
0, 0, 0, 0,

Now this is a diagonal flip (EDIT: It just occurs to me that this will keep x in the same position: perhaps this is what you mean?), but just do a horisontal flip and it should be fine:

for (int i=0; i<4; i++)
    for (int j=0; j<4; j++)
        rotate[i][3-j] = start[j][i];

Rotate finishes with:

0, 0, 0, 0,
1, 1, 0, 0,
0, 1, 1, 0,
0, 0, 0, 0,

(To tilt other way: rotate[i][j] = start[j][3-i];)

:)