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

using System;
using System.Collections.Generic;
using System.Linq;
using Silk.NET.Windowing;

namespace AcDream.App.Rendering;

/// <summary>
/// #391 (user-directed, 2026-08-13): the ONE source of the resolutions the
/// client offers. Production enumerates the display's real mode list
/// (<see cref="IMonitor.GetAllVideoModes"/>) and curates it to modern
/// widescreen formats that fit the desktop; the Config dropdown, and later
/// the fullscreen mode-switch validation (#376/#388), read the same catalog
/// so an offered mode is by construction a supported one.
///
/// <para>Retail deviation, register-rowed with #391: retail listed the
/// adapter's complete enumeration including 4:3 legacy modes and authored
/// <c>800x600</c> as the Config default
/// (<c>gmConfigUI::InitOptions SetDefaultValue(0x03200258)</c>). We curate
/// deliberately — modern formats only — and the Defaults value becomes the
/// desktop's own mode (always present in the curated list).</para>
///
/// <para>Write-once static owner: the catalog is immutable hardware truth
/// captured at startup on the windowing thread (the same shape as the
/// platform facts <c>GraphicalHostPlatformServices</c> owns). Fixture,
/// UI-Studio, and headless callers never install one and fall back to
/// <c>DisplaySettings.AvailableResolutions</c> at the consuming seam.</para>
/// </summary>
internal static class DisplayModeCatalog
{
    private static IReadOnlyList<string>? _resolutions;
    private static string? _desktopResolution;

    /// <summary>The curated list, or null when no catalog was installed
    /// (fixture/headless callers — consumers fall back to the static
    /// preset ladder).</summary>
    public static IReadOnlyList<string>? Resolutions => _resolutions;

    /// <summary>The desktop's current mode as a "WxH" string — the Config
    /// Resolution row's Defaults value in production (see the class doc for
    /// why this replaces retail's authored 800x600). Null when no catalog
    /// was installed.</summary>
    public static string? DesktopResolution => _desktopResolution;

    /// <summary>Captures the catalog from the window's monitor at startup.
    /// A null monitor or an empty curated result leaves the catalog
    /// uninstalled (consumers keep the static fallback). Safe to call once
    /// per process launch; a repeat call overwrites with equally-fresh
    /// hardware truth.</summary>
    public static void InstallFromWindow(IWindow window)
    {
        ArgumentNullException.ThrowIfNull(window);
        IMonitor? monitor = window.Monitor;
        if (monitor is null)
            return;

        VideoMode current = monitor.VideoMode;
        if (current.Resolution is not { } desktop || desktop.X <= 0 || desktop.Y <= 0)
            return;

        IEnumerable<(int W, int H)> modes = monitor
            .GetAllVideoModes()
            .Select(m => m.Resolution)
            .Where(r => r.HasValue)
            .Select(r => (r!.Value.X, r.Value.Y));

        IReadOnlyList<string> curated = Curate(modes, (desktop.X, desktop.Y));
        if (curated.Count == 0)
            return;

        _resolutions = curated;
        _desktopResolution = $"{desktop.X}x{desktop.Y}";
    }

    /// <summary>Test seam: clears the installed catalog.</summary>
    internal static void ResetForTests()
    {
        _resolutions = null;
        _desktopResolution = null;
    }

    /// <summary>
    /// The pure curation rule (#391): keep a mode iff
    ///  - it is a modern widescreen format (16:9, 16:10, or ultrawide 21:9 /
    ///    32:9, matched with a small tolerance so 1366x768 and friends pass),
    ///  - it is at least 1280 wide (no legacy-era sizes), and
    ///  - it fits the desktop (a windowed pick larger than the desktop can
    ///    only silently clamp — if it cannot exist, it is not offered).
    /// The desktop mode itself is always included even if its aspect is
    /// unusual (it is by definition displayable), refresh-rate duplicates
    /// collapse to one WxH entry, and the list sorts ascending by width then
    /// height so the dropdown reads naturally.
    /// </summary>
    internal static IReadOnlyList<string> Curate(
        IEnumerable<(int W, int H)> modes,
        (int W, int H) desktop)
    {
        // The modern aspect families, as width/height ratios.
        ReadOnlySpan<float> modernAspects =
        [
            16f / 9f,
            16f / 10f,
            21f / 9f,
            32f / 9f,
        ];

        var keep = new SortedSet<(int W, int H)>(
            Comparer<(int W, int H)>.Create(static (a, b) =>
                a.W != b.W ? a.W.CompareTo(b.W) : a.H.CompareTo(b.H)));

        foreach ((int w, int h) in modes)
        {
            if (w <= 0 || h <= 0)
                continue;
            if (w > desktop.W || h > desktop.H)
                continue;
            if ((w, h) == desktop)
            {
                keep.Add((w, h));
                continue;
            }
            if (w < 1280)
                continue;

            float aspect = w / (float)h;
            bool modern = false;
            foreach (float family in modernAspects)
            {
                // ±2.5% covers the near-miss members of a family (1366x768 is
                // 1.7786 vs 16:9's 1.7778; 3440x1440 is 2.3889 vs 21:9's
                // 2.3333, a 2.4% miss — while a real 4:3 (1.3333) or 5:4
                // (1.25) stays an order of magnitude outside every family).
                if (MathF.Abs(aspect - family) <= family * 0.025f)
                {
                    modern = true;
                    break;
                }
            }
            if (modern)
                keep.Add((w, h));
        }

        return keep.Select(static m => $"{m.W}x{m.H}").ToArray();
    }
}