UnityEditor.TextureUtil.GetGPUWidth C# (CSharp) Method

        public static extern int GetGPUWidth(Texture t);
        [MethodImpl(MethodImplOptions.InternalCall)]

        public override void OnInspectorGUI()
        {
            if (this.m_Images == null)
            {
                this.InitTexturesFromCubemap();
            }
            EditorGUIUtility.labelWidth = 50f;
            Cubemap cubemap = this.target as Cubemap;

            if (cubemap == null)
            {
                return;
            }
            GUILayout.BeginVertical(new GUILayoutOption[0]);
            GUILayout.BeginHorizontal(new GUILayoutOption[0]);
            this.ShowFace("Right\n(+X)", CubemapFace.PositiveX);
            this.ShowFace("Left\n(-X)", CubemapFace.NegativeX);
            GUILayout.EndHorizontal();
            GUILayout.BeginHorizontal(new GUILayoutOption[0]);
            this.ShowFace("Top\n(+Y)", CubemapFace.PositiveY);
            this.ShowFace("Bottom\n(-Y)", CubemapFace.NegativeY);
            GUILayout.EndHorizontal();
            GUILayout.BeginHorizontal(new GUILayoutOption[0]);
            this.ShowFace("Front\n(+Z)", CubemapFace.PositiveZ);
            this.ShowFace("Back\n(-Z)", CubemapFace.NegativeZ);
            GUILayout.EndHorizontal();
            GUILayout.EndVertical();
            EditorGUIUtility.labelWidth = 0f;
            EditorGUILayout.Space();
            EditorGUI.BeginChangeCheck();
            EditorGUILayout.HelpBox("Lowering face size is a destructive operation, you might need to re-assign the textures later to fix resolution issues. It's preferable to use Cubemap texture import type instead of Legacy Cubemap assets.", MessageType.Warning);
            int num = TextureUtil.GetGPUWidth(cubemap);

            num = EditorGUILayout.IntPopup("Face size", num, CubemapInspector.kSizes, CubemapInspector.kSizesValues, new GUILayoutOption[0]);
            int  mipmapCount = TextureUtil.GetMipmapCount(cubemap);
            bool useMipmap   = EditorGUILayout.Toggle("MipMaps", mipmapCount > 1, new GUILayoutOption[0]);
            bool flag        = TextureUtil.GetLinearSampled(cubemap);

            flag = EditorGUILayout.Toggle("Linear", flag, new GUILayoutOption[0]);
            bool flag2 = TextureUtil.IsCubemapReadable(cubemap);

            flag2 = EditorGUILayout.Toggle("Readable", flag2, new GUILayoutOption[0]);
            if (EditorGUI.EndChangeCheck())
            {
                if (TextureUtil.ReformatCubemap(ref cubemap, num, num, cubemap.format, useMipmap, flag))
                {
                    this.InitTexturesFromCubemap();
                }
                TextureUtil.MarkCubemapReadable(cubemap, flag2);
                cubemap.Apply();
            }
        }