BakeCubemap.cs

using UnityEngine;
using UnityEditor;
using System.IO;

public class BakeCubemap : ScriptableWizard
{
    public Transform CapturePosition;

    public int Antialiasing = 4;
    public int CubemapResolution = 128;

    public const string OutputDirectory = "Resources\\Generated\\Cubemaps";

    public void OnWizardCreate()
    {
        if (CapturePosition == null)
        {
            Debug.LogWarning("Setup render position");
            return;
        }

        var obj = new GameObject("BakeCubema_Camera");
        var cam = obj.AddComponent<Camera>();

        cam.gameObject.transform.position = CapturePosition.position;

        cam.backgroundColor = Color.black;
        cam.clearFlags      = CameraClearFlags.Skybox;
        cam.fieldOfView     = 90.0f;
        cam.aspect          = 1.0f;

        var FullPath = Path.Combine(Application.dataPath, OutputDirectory);

        if (Directory.Exists(FullPath) == false)
        {
            Directory.CreateDirectory(FullPath);
        }
        var tex = new Texture2D(CubemapResolution, 6 * CubemapResolution, TextureFormat.ARGB32, false);
        var rct = new Rect(0, 0, CubemapResolution, CubemapResolution);

        cam.targetTexture = RenderTexture.GetTemporary(CubemapResolution, CubemapResolution, 24, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Default, 1);
        var prevRT = RenderTexture.active;
        RenderTexture.active = cam.targetTexture;

        cam.gameObject.transform.rotation = Quaternion.Euler(0.0f, -90.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 0 * CubemapResolution, false);

        cam.gameObject.transform.rotation = Quaternion.Euler(0.0f, +90.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 1 * CubemapResolution, false);

        cam.gameObject.transform.rotation = Quaternion.Euler(+90.0f, +90.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 2 * CubemapResolution, false);

        cam.gameObject.transform.rotation = Quaternion.Euler(-90.0f, +90.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 3 * CubemapResolution, false);

        cam.gameObject.transform.rotation = Quaternion.Euler(0.0f, 0.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 4 * CubemapResolution, false);

        cam.gameObject.transform.rotation = Quaternion.Euler(0.0f, 180.0f, 0.0f);
        cam.Render();
        tex.ReadPixels(rct, 0, 5 * CubemapResolution, false);

        RenderTexture.ReleaseTemporary(cam.targetTexture);
        RenderTexture.active = prevRT;

        byte[] texData = tex.EncodeToPNG();

        var SavePath = Path.Combine(Path.Combine("Assets", OutputDirectory), CapturePosition.gameObject.name + ".png");

        File.WriteAllBytes(SavePath, texData);

        AssetDatabase.ImportAsset(SavePath, ImportAssetOptions.ForceUpdate);
        AssetDatabase.Refresh();

        DestroyImmediate(obj);
    }

    public void OnWizardOtherButton()
    {

    }

    public void OnWizardUpdate()
    {

    }

    [MenuItem ("Texture Generator/Bake Cubemap")]
    static void CreateWizard ()
    {
        ScriptableWizard.DisplayWizard<BakeCubemap>("Bake Cubemap", "Create", "Apply");
    }
}