BVH8 Structure

/// <summary>
/// 8-ary Bounding Volume Hierarchy node
///
/// The storage is deon in a way where base point (origin) of the local grid is used and bounds
/// for all 8 children are stored in quantized form. With 8 bits per plane. The scale of grid
/// is defined using exponent for each axis.
/// </summary>
struct ALIGN(16) BVH8Node
{
    /// <summary>
    /// Origin point of the local grid
    /// </summary>
    Engine::float3 mPoint;

    /// <summary>
    /// Exponent for each axis (8-bit)
    /// </summary>
    unsigned char mExponent[3];

    /// <summary>
    /// Mask to determine which child is leaf and which is interior node
    /// </summary>
    unsigned char mMask;

    /// <summary>
    /// Index to first referenced child node
    /// </summary>
    unsigned int mBaseChild;

    /// <summary>
    /// Index to first referenced triangle
    /// </summary>
    unsigned int mBaseTriangle;

    /// <summary>
    /// Per-child meta information encoding the indexing information required to find corresponding
    /// triangle range or node in the corresponding array
    ///
    /// Empty child slot - encoded as 00000000
    /// Internal node - encoded as high 3-bits 001 and low 5-bits store child slot index plus 24
    /// Leaf node - encoded as high 3-bitss storing number of triangles using unary encoding and
    ///             low 5 bits store inde of first triangle relative to triangle base index
    /// </summary>
    unsigned char mMeta[8];

    /// <summary>
    /// Quantized bounding box min on X axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMinX[8];

    /// <summary>
    /// Quantized bounding box max on X axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMaxX[8];

    /// <summary>
    /// Quantized bounding box min on Y axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMinY[8];

    /// <summary>
    /// Quantized bounding box max on Y axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMaxY[8];

    /// <summary>
    /// Quantized bounding box min on Z axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMinZ[8];

    /// <summary>
    /// Quantized bounding box max on Z axis for all 8 children
    /// </summary>
    unsigned char mQuantizedMaxZ[8];

    /// <summary>
    /// Is child node a leaf?
    /// </summary>
    /// <param name="childIndex">Nth child node</param>
    /// <returns>True when leaf, false otherwise</returns>
    inline bool IsLeaf(int childIndex)
    {
        return (mMeta[childIndex] & 0b00011111) << 24;
    }
};