diff -r 896250d050e9 src/window.cpp
--- a/src/window.cpp	Thu Mar 05 20:45:54 2009 +0100
+++ b/src/window.cpp	Thu Mar 05 20:48:05 2009 +0100
@@ -27,6 +27,7 @@
 #include "table/sprites.h"
 
 static Point _drag_delta; ///< delta between mouse cursor and upper left corner of dragged window
+static bool _resize_left_edge; ///< Left edge of the window is being resized.
 static Window *_mouseover_last_w = NULL; ///< Window of the last MOUSEOVER event
 
 /** List of windows opened at the screen sorted from the front. */
@@ -211,7 +212,7 @@
 }
 
 static void StartWindowDrag(Window *w);
-static void StartWindowSizing(Window *w);
+static void StartWindowSizing(Window *w, bool leftedge);
 
 /**
  * Dispatch left mouse-button (possibly double) click in window.
@@ -305,7 +306,7 @@
 		}
 
 		if (w->desc_flags & WDF_RESIZABLE && wi->type == WWT_RESIZEBOX) {
-			StartWindowSizing(w);
+			StartWindowSizing(w, (wi->left < 10)); // less than 10 -> resize-box is connected to left-edge
 			w->InvalidateWidget(widget);
 			return;
 		}
@@ -1497,7 +1498,14 @@
 				break;
 			}
 
-			x = _cursor.pos.x - _drag_delta.x;
+			/* Compute difference in pixels between cursor position and reference point in the window.
+			 * If resizing the left edge of the window, moving to the left makes the window bigger not smaller.
+			 */
+			if (_resize_left_edge) {
+				x = _drag_delta.x - _cursor.pos.x;
+			} else {
+				x = _cursor.pos.x - _drag_delta.x;
+			}
 			y = _cursor.pos.y - _drag_delta.y;
 
 			/* X and Y has to go by step.. calculate it.
@@ -1518,9 +1526,18 @@
 
 			/* Now find the new cursor pos.. this is NOT _cursor, because
 			    we move in steps. */
-			_drag_delta.x += x;
+			if (_resize_left_edge) {
+				_drag_delta.x -= x; // x>0 -> window gets longer -> left-edge moves to left -> subtract x to get new position.
+			} else {
+				_drag_delta.x += x;
+			}
 			_drag_delta.y += y;
 
+			if (_resize_left_edge && x != 0) {
+				w->SetDirty();
+				w->left -= x;  // If dragging left edge, move left window edge in opposite direction by the same amount.
+				/* ResizeWindow() below ensures marking new position as dirty. */
+			}
 			/* ResizeWindow sets both pre- and after-size to dirty for redrawal */
 			ResizeWindow(w, x, y);
 
@@ -1556,16 +1573,18 @@
 }
 
 /**
- * Start resizing a window
- * @param w Window to start resizing
+ * Start resizing a window.
+ * @param w        Window to start resizing.
+ * @param leftedge Left edge of the window is being dragged.
  */
-static void StartWindowSizing(Window *w)
+static void StartWindowSizing(Window *w, bool leftedge)
 {
 	w->flags4 |= WF_SIZING;
 	_dragging_window = true;
 
 	_drag_delta.x = _cursor.pos.x;
 	_drag_delta.y = _cursor.pos.y;
+	_resize_left_edge = leftedge;
 
 	BringWindowToFront(w);
 	DeleteWindowById(WC_DROPDOWN_MENU, 0);