namespace MrGameEng.Graphics;

/// <summary>
/// Builds the 64-bit sort key the batcher orders sprites by:
/// layer (8 bits) → depth (32 bits) → texture (24 bits).
/// Texture bits only group equal textures for batching; collisions are harmless.
/// </summary>
public static class SpriteSortKey
{
    /// <summary>Composes a sort key from layer, depth and texture grouping key.</summary>
    public static ulong Make(byte layer, float depth, int textureKey) =>
        ((ulong)layer << 56)
        | ((ulong)DepthToSortableBits(depth) << 24)
        | ((uint)textureKey & 0xFF_FFFF);

    /// <summary>
    /// Maps a float to bits whose unsigned order matches the float order
    /// (negative depths sort before positive ones).
    /// </summary>
    public static uint DepthToSortableBits(float depth)
    {
        var bits = BitConverter.SingleToUInt32Bits(depth);
        return (bits & 0x8000_0000) != 0 ? ~bits : bits | 0x8000_0000;
    }
}