Index: src/variables.h
===================================================================
--- src/variables.h	(revision 11132)
+++ src/variables.h	(working copy)
@@ -337,6 +337,8 @@
 
 extern const TileTypeProcs * const _tile_type_procs[16];
 
+extern bool _draw_bounding_boxes;
+
 /* misc */
 VARDEF char _screenshot_name[128];
 VARDEF byte _vehicle_design_names;
Index: src/gfx.h
===================================================================
--- src/gfx.h	(revision 11132)
+++ src/gfx.h	(working copy)
@@ -268,6 +268,7 @@
 
 void GfxFillRect(int left, int top, int right, int bottom, int color);
 void GfxDrawLine(int left, int top, int right, int bottom, int color);
+void DrawBox(int x, int y, int dx1, int dy1, int dx2, int dy2, int dx3, int dy3);
 
 BoundingRect GetStringBoundingBox(const char *str);
 uint32 FormatStringLinebreaks(char *str, int maxw);
Index: src/viewport.cpp
===================================================================
--- src/viewport.cpp	(revision 11132)
+++ src/viewport.cpp	(working copy)
@@ -551,11 +551,15 @@
 	pt = RemapCoords(x, y, z);
 	ps->x = pt.x;
 	ps->y = pt.y;
+	int bb_left = RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x;
+	int bb_right = RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x;
+	int bb_top = RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y;
+	int bb_bottom = RemapCoords(x + w          , y + h          , z + bb_offset_z).y;
 	if (image == SPR_EMPTY_BOUNDING_BOX) {
-		ps->left = RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x;
-		right    = RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x;
-		ps->top  = RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y;
-		bottom   = RemapCoords(x + w          , y + h          , z + bb_offset_z).y;
+		ps->left = bb_left;
+		right    = bb_right;
+		ps->top  = bb_top;
+		bottom   = bb_bottom;
 	} else {
 		const Sprite *spr = GetSprite(image & SPRITE_MASK);
 		ps->left = (pt.x += spr->x_offs);
@@ -563,10 +567,14 @@
 		ps->top  = (pt.y += spr->y_offs);
 		bottom   = (pt.y +  spr->height);
 	}
-	if (ps->left >= vd->dpi.left + vd->dpi.width ||
-	    right    <= vd->dpi.left ||
-	    ps->top  >= vd->dpi.top + vd->dpi.height ||
-	    bottom   <= vd->dpi.top) {
+	bb_left = min(bb_left, ps->left);
+	bb_right = max(bb_right, right);
+	bb_top = min(bb_top, ps->top);
+	bb_bottom = max(bb_bottom, bottom);
+	if (bb_left   >= vd->dpi.left + vd->dpi.width ||
+	    bb_right  <= vd->dpi.left ||
+	    bb_top    >= vd->dpi.top + vd->dpi.height ||
+	    bb_bottom <= vd->dpi.top) {
 		return;
 	}
 
@@ -1231,6 +1239,22 @@
 	}
 }
 
+static void ViewportDrawBoundingBoxes(ParentSpriteToDraw *psd[])
+{
+	for (; *psd != NULL; psd++) {
+		const ParentSpriteToDraw* ps = *psd;
+		Point pt1 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmax + 1);
+		Point pt2 = RemapCoords(ps->xmin    , ps->ymax + 1, ps->zmax + 1);
+		Point pt3 = RemapCoords(ps->xmax + 1, ps->ymin    , ps->zmax + 1);
+		Point pt4 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmin    );
+
+		DrawBox(        pt1.x,         pt1.y,
+		        pt2.x - pt1.x, pt2.y - pt1.y,
+		        pt3.x - pt1.x, pt3.y - pt1.y,
+		        pt4.x - pt1.x, pt4.y - pt1.y);
+	}
+}
+
 static void ViewportDrawStrings(DrawPixelInfo *dpi, const StringSpriteToDraw *ss)
 {
 	DrawPixelInfo dp;
@@ -1354,6 +1378,7 @@
 
 	ViewportSortParentSprites(parent_list);
 	ViewportDrawParentSprites(parent_list);
+	if (_draw_bounding_boxes) ViewportDrawBoundingBoxes(parent_list);
 
 	if (vd.first_string != NULL) ViewportDrawStrings(&vd.dpi, vd.first_string);
 
Index: src/gfx.cpp
===================================================================
--- src/gfx.cpp	(revision 11132)
+++ src/gfx.cpp	(working copy)
@@ -139,7 +139,36 @@
 	blitter->DrawLine(dpi->dst_ptr, x, y, x2, y2, dpi->width, dpi->height, color);
 }
 
+/**
+ * Draws the projection of a parallelepiped.
+ * This can be used to draw boxes in world coordinates.
+ *
+ * @param x   Screen X-coordinate of top front corner.
+ * @param y   Screen Y-coordinate of top front corner.
+ * @param dx1 Screen X-length of first edge.
+ * @param dy1 Screen Y-length of first edge.
+ * @param dx2 Screen X-length of second edge.
+ * @param dy2 Screen Y-length of second edge.
+ * @param dx3 Screen X-length of third edge.
+ * @param dy3 Screen Y-length of third edge.
+ */
+void DrawBox(int x, int y, int dx1, int dy1, int dx2, int dy2, int dx3, int dy3)
+{
+	static const byte color = 255;
 
+	GfxDrawLine(x, y, x + dx1, y + dy1, color);
+	GfxDrawLine(x, y, x + dx2, y + dy2, color);
+	GfxDrawLine(x, y, x + dx3, y + dy3, color);
+
+	GfxDrawLine(x + dx1, y + dy1, x + dx1 + dx2, y + dy1 + dy2, color);
+	GfxDrawLine(x + dx1, y + dy1, x + dx1 + dx3, y + dy1 + dy3, color);
+	GfxDrawLine(x + dx2, y + dy2, x + dx2 + dx1, y + dy2 + dy1, color);
+	GfxDrawLine(x + dx2, y + dy2, x + dx2 + dx3, y + dy2 + dy3, color);
+	GfxDrawLine(x + dx3, y + dy3, x + dx3 + dx1, y + dy3 + dy1, color);
+	GfxDrawLine(x + dx3, y + dy3, x + dx3 + dx2, y + dy3 + dy2, color);
+}
+
+
 /** Truncate a given string to a maximum width if neccessary.
  * If the string is truncated, add three dots ('...') to show this.
  * @param *str string that is checked and possibly truncated
Index: src/main_gui.cpp
===================================================================
--- src/main_gui.cpp	(revision 11132)
+++ src/main_gui.cpp	(working copy)
@@ -59,7 +59,9 @@
 extern void GenerateIndustries();
 extern bool GenerateTowns();
 
+bool _draw_bounding_boxes = false;
 
+
 void CcGiveMoney(bool success, TileIndex tile, uint32 p1, uint32 p2)
 {
 #ifdef ENABLE_NETWORK
@@ -2262,6 +2264,11 @@
 				ToggleTransparency();
 				break;
 
+			case 'B' | WKC_CTRL:
+				_draw_bounding_boxes = !_draw_bounding_boxes;
+				MarkWholeScreenDirty();
+				break;
+
 #ifdef ENABLE_NETWORK
 			case WKC_RETURN: case 'T': // smart chat; send to team if any, otherwise to all
 				if (_networking) {