UnityEditor上で、Camera.Renderを使用するパターンでの、マルチディスプレイ対応スクリプト

EditorMultiDisplayDrawer.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using UnityEngine;

public class EditorMultiDisplayDrawer
{
#if UNITY_EDITOR
    Type type;
    FieldInfo targetTextureField;
    FieldInfo targetDisplayField;

    List<UnityEditor.EditorWindow> gameWindows;

    public EditorMultiDisplayDrawer()
    {
        gameWindows = new List<UnityEditor.EditorWindow>();
        // 表示中のウィンドウ一覧を取得するので、GameViewのウィンドウを抽出する
        gameWindows.AddRange(Resources.FindObjectsOfTypeAll<UnityEditor.EditorWindow>()
            .Where(x => x.titleContent.text == "Game"));

        type = type ?? typeof(UnityEditor.EditorWindow).Assembly.GetType("UnityEditor.GameView");
        // TargetDisplayの番号と、画面表示用のRenderTextureを取得
#if UNITY_2019_3_OR_NEWER
        targetTextureField = type.GetField("m_RenderTexture", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
#else
        targetTextureField = type.GetField("m_TargetTexture", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
#endif
        targetDisplayField = type.GetField("m_TargetDisplay", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
    }

    public void Draw(Camera camera, int targetDisplay)
    {
        // 同一TargetDisplayのウィンドウを探す
        var gameWindow = gameWindows.FirstOrDefault(x => targetDisplay == (int)targetDisplayField.GetValue(x));
        if (!gameWindow)
            return;

        // GameView描画用のRenderTextureを取得
        var gameviewRenderTexture = (RenderTexture)targetTextureField.GetValue(gameWindow);
        if (!gameviewRenderTexture)
            return;

        // 画面左下が基準の場合はひっくり返す
        if (SystemInfo.graphicsUVStartsAtTop)
        {
            camera.projectionMatrix = camera.projectionMatrix * Matrix4x4.Scale(new Vector3(1, -1, 1));
        }

        camera.targetTexture = gameviewRenderTexture;
        camera.Render();
        camera.ResetProjectionMatrix();
    }
#else
    public void Draw(Camera camera, int targetDisplay){}
#endif
}