Turning a Nested 2D Loop into 1D

In GPU programming, you might sample a 2D window with a nested. However, a nested loop might be more inefficient than 1 loop.

This post is an example of how to sample a 3x3 window of offsets in 1 loop.

Source Code

// Get required data to calculate main window data
const int WindowSize = 3;
const int WindowHalf = trunc(WindowSize / 2);

// Start from the negative so we can process a window in 1 loop
[loop] for (int i = 0; i < (WindowSize * WindowSize); i++)
{
   float2 XY = -WindowHalf + float2(i % WindowSize, trunc(i / WindowSize));
}

Note

i#		X		Y
0	-1 + (0 % 3)	-1	-1 + trunc(0 / 3)	-1
1	-1 + (1 % 3)	0	-1 + trunc(1 / 3)	-1
2	-1 + (2 % 3)	1	-1 + trunc(2 / 3)	-1
3	-1 + (3 % 3)	-1	-1 + trunc(3 / 3)	0
4	-1 + (4 % 3)	0	-1 + trunc(4 / 3)	0
5	-1 + (5 % 3)	1	-1 + trunc(5 / 3)	0
6	-1 + (6 % 3)	-1	-1 + trunc(6 / 3)	1
7	-1 + (7 % 3)	0	-1 + trunc(7 / 3)	1
8	-1 + (8 % 3)	1	-1 + trunc(8 / 3)	1