UnityEngine.Rect.ScaleSizeBy(UnityEngine.Vector2, UnityEngine.Vector2)

public static Rect ScaleSizeBy(this Rect rect, float scale)
        {
            return rect.ScaleSizeBy(scale, rect.center);
        }

public static Rect ScaleSizeBy(this Rect rect, Vector2 scale)
        {
            return rect.ScaleSizeBy(scale, rect.center);
        }

public static Rect Begin(float zoomScale, Rect screenCoordsArea)
        {
            GUI.EndGroup();        // End the group Unity begins automatically for an EditorWindow to clip out the window tab. This allows us to draw outside of the size of the EditorWindow.
            
            Rect clippedArea = screenCoordsArea.ScaleSizeBy(1.0f / zoomScale, screenCoordsArea.TopLeft());
            clippedArea.position += offset;
            GUI.BeginGroup(clippedArea);
            
            _prevGuiMatrix = GUI.matrix;

            Matrix4x4 translation = Matrix4x4.TRS(clippedArea.TopLeft(), Quaternion.idenreplacedy, Vector3.one);
            Matrix4x4 scale = Matrix4x4.Scale(new Vector3(zoomScale, zoomScale, 1.0f));
            GUI.matrix = translation * scale * translation.inverse * GUI.matrix;
            

            return clippedArea;
        }