acdream/src/AcDream.App/Rendering/BindlessTexturePair.cs

namespace AcDream.App.Rendering;

/// <summary>
/// Owns the two independent residency edges used by TerrainAtlas. Acquisition
/// and release publish each successful edge immediately, so a partial failure
/// retries only work that is still pending.
/// </summary>
internal sealed class BindlessTexturePair(
    uint firstTexture,
    uint secondTexture,
    Func<uint, ulong> acquire,
    Action<ulong> release)
{
    private ulong _firstHandle;
    private ulong _secondHandle;
    private bool _firstResident;
    private bool _secondResident;

    public bool IsFullyResident => _firstResident && _secondResident;
    public bool HasAnyResident => _firstResident || _secondResident;

    public (ulong First, ulong Second) Acquire()
    {
        if (!_firstResident)
        {
            _firstHandle = acquire(firstTexture);
            _firstResident = true;
        }

        if (!_secondResident)
        {
            try
            {
                _secondHandle = acquire(secondTexture);
                _secondResident = true;
            }
            catch (Exception acquisitionFailure)
            {
                try
                {
                    Release();
                }
                catch (Exception cleanupFailure)
                {
                    throw new AggregateException(
                        "Second bindless texture acquisition failed and the resident prefix did not cleanly roll back.",
                        acquisitionFailure,
                        cleanupFailure);
                }

                throw;
            }
        }

        return (_firstHandle, _secondHandle);
    }

    public void Release()
    {
        List<Exception>? failures = null;
        if (_firstResident)
        {
            try
            {
                release(_firstHandle);
                _firstResident = false;
                _firstHandle = 0;
            }
            catch (Exception failure)
            {
                (failures ??= []).Add(failure);
            }
        }

        if (_secondResident)
        {
            try
            {
                release(_secondHandle);
                _secondResident = false;
                _secondHandle = 0;
            }
            catch (Exception failure)
            {
                (failures ??= []).Add(failure);
            }
        }

        if (failures is not null)
            throw new AggregateException(
                "One or more bindless texture handles could not be made non-resident.",
                failures);
    }
}