using AcDream.Core.Terrain;

namespace AcDream.Core.Meshing;

/// <summary>
/// One sub-mesh of a GfxObj: a vertex+index buffer that uses a single Surface.
/// A GfxObj with multiple surfaces produces multiple sub-meshes.
/// </summary>
public sealed record GfxObjSubMesh(
    uint SurfaceId,
    Vertex[] Vertices,
    uint[] Indices)
{
    /// <summary>
    /// How this sub-mesh should be composited into the frame.
    /// Populated from Surface.Type flags at upload time.
    /// </summary>
    public TranslucencyKind Translucency { get; init; } = TranslucencyKind.Opaque;

    /// <summary>
    /// Surface.Luminosity. Retail uses this as material emissive.
    /// </summary>
    public float Luminosity { get; init; } = 0f;

    /// <summary>
    /// Surface.Diffuse. Retail sky keyframes route SkyObjectReplace.MaxBright
    /// through CPhysicsObj::SetDiffusion (0x005119e0), which lands in
    /// CMaterial::SetDiffuseSimple (0x00539750).
    /// </summary>
    public float Diffuse { get; init; } = 1f;

    /// <summary>
    /// True when at least one vertex UV component lies outside [0, 1], so
    /// the mesh expects texture repeat instead of clamp.
    /// </summary>
    public bool NeedsUvRepeat { get; init; } = false;

    /// <summary>
    /// Final opacity multiplier derived from Surface.Translucency. Retail
    /// translucency is transparency: 0.0 is opaque and 1.0 is invisible.
    /// CMaterial::SetTranslucencySimple at 0x005396f0 writes material alpha
    /// as 1 - translucency.
    /// </summary>
    public float SurfOpacity { get; init; } = 1f;

    /// <summary>
    /// True when the raw Surface.Type has the Additive bit. Retail disables
    /// fixed-function fog alpha for this raw bit even if the final blend mode
    /// is forced to AlphaBlend by the Translucent+ClipMap branch.
    /// </summary>
    public bool DisableFog { get; init; } = false;
}