using System;
using System.Runtime.InteropServices;
using ImGuiNET;

class FontConfigWrap : IDisposable
{
    ImFontConfig[] _config;

    public delegate void EnterFunc(ref ImFontConfig config);

    public void Enter(EnterFunc callback)
    {
        callback(ref _config[0]);
    }

    GCHandle _pinnedArray;

    public IntPtr Ptr => _pinnedArray.AddrOfPinnedObject();

    public FontConfigWrap()
    {
        // from im_draw.cpp: ImFontConfig::ImFontConfig
        _config = new ImFontConfig[]
        {
                new ImFontConfig{
                    FontDataOwnedByAtlas = 1,
                    OversampleH = 3, // FIXME: 2 may be a better default?
                    OversampleV = 1,
                    GlyphMaxAdvanceX = float.MaxValue,
                    RasterizerMultiply = 1.0f,
                    EllipsisChar = ushort.MaxValue,
                }
        };
        // 要素数１のArrayを利用して struct の IntPtr を得る
        _pinnedArray = GCHandle.Alloc(_config, GCHandleType.Pinned);
    }

    public void Dispose()
    {
        if (_pinnedArray.IsAllocated)
        {
            _pinnedArray.Free();
        }
    }
}

using UnityEngine;
using ImGuiNET;


public class MSGothic : MonoBehaviour
{

    // Start is called before the first frame update
    public void LoadMSGothic()
    {
        Debug.Log("LoadMSGothic");
        var io = ImGui.GetIO();

#if false
        io.Fonts.AddFontDefault();
        io.Fonts.Build();
#else
        io.Fonts.AddFontDefault();

        using (var config = new FontConfigWrap())
        {
            config.Enter((ref ImFontConfig config) =>
            {
                config.MergeMode = 1;
            });

            io.Fonts.AddFontFromFileTTF("C:/Windows/Fonts/MSGothic.ttc", 24, config.Ptr, io.Fonts.GetGlyphRangesJapanese());
            io.Fonts.Build();
        }
#endif
    }

    private void OnEnable()
    {
        UImGui.UImGuiUtility.Layout += OnLayout;
    }

    private void OnDisable()
    {
        UImGui.UImGuiUtility.Layout -= OnLayout;
    }

    private void OnLayout(UImGui.UImGui uImGui)
    {
        if (ImGui.Begin("日本語"))
        {
            ImGui.TextUnformatted("テキスト");
        }
        ImGui.End();
    }
}