Extract GetExpansionFromSize method

(cherry picked from commit c1360823e78f1aea87b5c287209b8e6b0db41210)
(cherry picked from commit c2df37eac74e9739e25e67397375135a76f46511)

src/Greenshot.Editor/Drawing/DrawableContainerList.cs

@@ -982,29 +982,10 @@ namespace Greenshot.Editor.Drawing
         /// <param name="targetElement"></param>
         public void PushOut(Direction direction, ISurface surface, IDrawableContainer targetElement)
         {
-            int left = 0, right = 0, top = 0, bottom = 0;
+            var expansion = GetExpansionFromSize(direction, targetElement.Size);
-
-            switch (direction)
-            {
-                case Direction.LEFT:
-                    left = targetElement.Width;
-                    break;
-                case Direction.RIGHT:
-                    right = targetElement.Width;
-                    break;
-                case Direction.TOP:
-                    top = targetElement.Height;
-                    break;
-                case Direction.BOTTOM:
-                    bottom = targetElement.Height;
-                    break;
-                default:
-                    break;
-            }
             
-            surface.ResizeCanvas(left, right, top, bottom);
+            surface.ResizeCanvas(expansion.Left, expansion.Right, expansion.Top, expansion.Bottom);
 
-            // Move target object
             SnapToEdge(direction, surface, targetElement);
 
             if (direction == Direction.LEFT || direction == Direction.RIGHT)
@@ -1014,5 +995,36 @@ namespace Greenshot.Editor.Drawing
 
             surface.DeselectAllElements();
         }
+
+        /// <summary>
+        /// Calculate the one-directional expansion needed to accommodate an element of the given size.
+        /// </summary>
+        /// <param name="direction">The direction in which to expand.</param>
+        /// <param name="elementSize">The size of the element to accommodate.</param>
+        /// <returns></returns>
+        public static Expansion GetExpansionFromSize(Direction direction, Size elementSize)
+        {
+            var expansion = new Expansion();
+
+            switch (direction)
+            {
+                case Direction.LEFT:
+                    expansion.Left = elementSize.Width;
+                    break;
+                case Direction.RIGHT:
+                    expansion.Right = elementSize.Width;
+                    break;
+                case Direction.TOP:
+                    expansion.Top = elementSize.Height;
+                    break;
+                case Direction.BOTTOM:
+                    expansion.Bottom = elementSize.Height;
+                    break;
+                default:
+                    break;
+            }
+
+            return expansion;
+        }
     }
 }

src/Greenshot.Editor/Drawing/Expansion.cs

@@ -0,0 +1,31 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2021 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: https://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+namespace Greenshot.Editor.Drawing
+{
+    public struct Expansion
+    {
+        public int Left;
+        public int Right;
+        public int Top;
+        public int Bottom;
+    }
+}