#define STEPS 250

struct BlackHoleProperties
{
    float Mass; // Mass of the Black Hole.
    float EventHorizon; // Black Hole Radius, Mass * 2
};

// Position of Blackhole assumed to be at the Origin

bool CrossedEventHorizon(float3 RayPos, BlackHoleProperties BHP)
{
    if (length(RayPos) <= BHP.EventHorizon)
    {
        return true;
    }
    return false;

}
float Cross2(float3 A, float3 B)
{
    return pow((A.y * B.z) - (A.z * B.y), 2) +
           pow((A.z * B.x) - (A.x * B.z), 2) +
           pow((A.x * B.y) - (A.y * B.x), 2);
}

float3 GravityForce(float3 RayPos, float3 RayDir, BlackHoleProperties BHP)
{
    RayDir = normalize(RayDir);
    float DistToSingularity = length(RayPos);
    float SquareDistance = DistToSingularity * DistToSingularity + 0.0001; // Prevent Divide by Zero
    float3 SingularityToPos = normalize(RayPos);

    return (-3.0 * BHP.Mass) / SquareDistance * Cross2(SingularityToPos, RayDir) * SingularityToPos;

}

void BlackHole(inout float4 Color, inout float Mask, inout float3 Dir, float3 CameraPosition, BlackHoleProperties BHP)
{
    float3 RayPos = CameraPosition;
    float3 RayDir = Dir;
    float3 PrevPos;

    //Begin Ray Marching
    for (int i = 0; i < STEPS; i++)
    {
        if (CrossedEventHorizon(RayPos, BHP))
        {
            Mask = 0;
            break;
        }
        PrevPos = RayPos;
        RayPos += RayDir + GravityForce(RayPos, RayDir, BHP);
        RayDir = normalize(RayPos - PrevPos);
    }
    Dir = RayDir;
}