import bindless;
import ibl_common;

float2 SampleSphericalMap(float3 v)
{
    const float2 InvTan = float2(0.1591f, 0.3183f);     // (1/2PI, 1/PI)
    float2 UV = float2(atan2(-v.x, v.z), asin(-v.y));   // (-PI, -PI/2) to (PI, PI/2)
    UV *= InvTan;                                       // (-1/2, -1/2) to (1/2, 1/2)
    UV += 0.5f.xx;                                      // (0, 0) to (1, 1)
    return UV;
}

struct Block {
    Sampler2D<float4>.Handle hdrEnv;
    RWTexture2DArray<float4>.Handle outputTexture;
    uint cubeSide;
};

[shader("compute")]
[numthreads(16, 16, 1)]
void main(
    uint3 GlobalInvocationID: SV_DispatchThreadID,
    uniform Block pcb
)
{
    float3 LocalDir = GetCubeDir(GlobalInvocationID, pcb.cubeSide);
    
    float2 UV = SampleSphericalMap(LocalDir);

    pcb.outputTexture[GlobalInvocationID.xyz] = pcb.hdrEnv.SampleLevel(UV, 0);
}