#include "bindless_structs.hlsli"

/*
 The Goal is simply to convert from a (0,0,0) to (CubeSide, CubeSide, FaceCount) Invocation ID space to a
 (-1,-1,-1) to (1, 1, 1) space.

| Axis | Layer | Up |
|:----:|:-----:|:--:|
|  +x  |   0   | -y |
|  -x  |   1   | -y |
|  +y  |   2   | +z |
|  -y  |   3   | -z |
|  -z  |   4   | -y |
|  +z  |   5   | -y |
*/
float3 GetCubeDir(uint3 GlobalInvocationID, float SideLength)
{
    float2 FaceUV = float2(GlobalInvocationID.xy) / SideLength; // (0, SideLength) -> (0, 1)
    FaceUV = 2.0f * FaceUV - 1.0f; // (0, 1) -> (-1, 1)
    
    switch (GlobalInvocationID.z)
    {
        case 0:
            return normalize(float3(1.0f, -FaceUV.y, -FaceUV.x)); // Face +X; x = 1, y = -v, z = -u
        case 1:
            return normalize(float3(-1.0f, -FaceUV.y, FaceUV.x)); // Face -X; x = -1, y = -v, z = u
        case 2:
            return normalize(float3(FaceUV.x, 1.0f, FaceUV.y)); // Face +Y; x = u, y = 1, z = v
        case 3:
            return normalize(float3(FaceUV.x, -1.0f, -FaceUV.y)); // Face -Y; x=u, y=-1, z=-v
        case 4:
            return normalize(float3(FaceUV.x, -FaceUV.y, 1.0f)); // Face +Z; x=u,y=-v, z=1
        case 5:
            return normalize(float3(-FaceUV.x, -FaceUV.y, -1.0f)); // Face -Z; x=u,y=-v, z=-1
        default:
            // Never reach here.
            return 0.0f.xxx;
    }
}