UnityEditor.ContainerWindow.SetAlpha C# (CSharp) Method

        public extern void SetAlpha(float alpha);
        [MethodImpl(MethodImplOptions.InternalCall)]

        protected override void OldOnGUI()
        {
            if (Event.current.type != EventType.Repaint)
            {
                return;
            }

            const float dragTabOffsetX = 2f;
            const float dragTabOffsetY = 2f;
            const float dragTabHeight  = 18f;

            float minWidth, expectedWidth;

            Styles.dragtab.CalcMinMaxWidth(m_Content, out minWidth, out expectedWidth);
            float tabWidth        = Mathf.Max(Mathf.Min(expectedWidth, Styles.tabMaxWidth), Styles.tabMinWidth) + Styles.tabWidthPadding;
            Rect  windowRect      = new Rect(0, 0, position.width, position.height);
            Rect  tabPositionRect = new Rect(dragTabOffsetX, dragTabOffsetY, tabWidth, dragTabHeight);
            float roundedPosX     = Mathf.Round(tabPositionRect.x);
            float roundedWidth    = Mathf.Round(tabPositionRect.x + tabPositionRect.width) - roundedPosX;
            Rect  tabContentRect  = new Rect(roundedPosX, tabPositionRect.y, roundedWidth, tabPositionRect.height);
            Rect  viewRect        = new Rect(dragTabOffsetX, tabContentRect.yMax - 2f,
                                             position.width - dragTabOffsetX * 2, position.height - tabContentRect.yMax - dragTabOffsetY + 2f);

            Styles.background.Draw(windowRect, GUIContent.none, false, false, true, true);
            Styles.dragtab.Draw(tabContentRect, false, true, false, false);
            Styles.view.Draw(viewRect, GUIContent.none, false, false, true, true);
            GUI.Label(tabPositionRect, m_Content, Styles.tabLabel);

            // We currently only support this on macOS
            m_Window.SetAlpha(m_TargetAlpha);
        }