Index: src/toolbar_gui.cpp
===================================================================
--- src/toolbar_gui.cpp	(revision 12872)
+++ src/toolbar_gui.cpp	(working copy)
@@ -50,6 +50,8 @@
 RailType _last_built_railtype;
 RoadType _last_built_roadtype;
 
+bool _switched_bar;
+
 static void SelectSignTool()
 {
 	if (_cursor.sprite == SPR_CURSOR_SIGN) {
@@ -516,6 +518,16 @@
 	}
 }
 
+/* --- Switch toolbar button --- */
+
+static void ToolbarSwitchClick(Window *w)
+{
+	_switched_bar ^= true;
+	CallWindowEventNP(w, WE_RESIZE);
+	SetWindowDirty(w);
+	SndPlayFx(SND_15_BEEP);
+}
+
 /* --- Scenario editor specific handlers. */
 
 static void ToolbarScenDateBackward(Window *w)
@@ -614,7 +626,89 @@
 {
 }
 
+/* --- Resizing the toolbar */
 
+void ResizeToolbar(Window *w)
+{
+	/* There are 27 buttons plus some spacings if the space allows it */
+	uint button_width;
+	uint spacing;
+	if (w->width >= 27 * 22) {
+		button_width = 22;
+		spacing = w->width - (27 * button_width);
+	} else {
+		button_width = w->width / 27;
+		spacing = 0;
+	}
+	uint extra_spacing_at[] = { 4, 8, 13, 17, 19, 24, 0 };
+
+	for (uint i = 0, x = 0, j = 0; i < 27; i++) {
+		if (extra_spacing_at[j] == i) {
+			j++;
+			uint add = spacing / (lengthof(extra_spacing_at) - j);
+			spacing -= add;
+			x += add;
+		}
+
+		w->widget[i].type = WWT_IMGBTN;
+		w->widget[i].left = x;
+		x += (spacing != 0) ? button_width : (w->width - x) / (27 - i);
+		w->widget[i].right = x - 1;
+	}
+
+	w->widget[27].type = WWT_EMPTY;
+}
+
+/* --- Split the toolbar */
+
+/* The order in which the buttons should be checked. This will determine the order they'll appear on screen. */
+uint split_order[] =    { 0, 1,  2,  3, 6, 13, 14, 15, 16, 19, 20,   21, 22, 23,  5,  7,  8, 9, 10, 12, 24, 25, 26,  4, 17, 18, 27, 11 };
+/* The priority determines on which toolbar the button will appear. The lowest number will (if possible) appear on both bars. Higher numbers only on the second bar. */
+uint split_priority[] = { 1, 2, 16, 26, 5, 17, 6, 18, 19, 20, 21, 0xFF, 22, 7, 8, 9, 10, 3, 4, 11, 13, 14, 15, 12, 23, 24, 25, 0 };
+
+void SplitToolbar(Window *w)
+{
+	uint icon_size = 22;
+	uint button_width = icon_size;
+	uint max_icons = w->width / icon_size;
+
+	if (max_icons < 14) {
+		button_width = w->width / 14;
+		max_icons = 14;
+	}
+
+	w->width = (max_icons - 1) * button_width + icon_size;
+
+	uint show_on_both = 2 * max_icons - 28; // 28 is total number of icons
+
+	for (uint i = 0, x = 0; i < 28; i++) {
+		uint icon = split_order[i];
+		uint priority = split_priority[icon];
+		bool show = false;
+
+		if (!_switched_bar)
+			show = (priority < max_icons);
+		else
+			show = (priority >= max_icons && priority != 0xFF); // special case for the Company League button. Menu will be merged with Graphs menu
+
+		if (priority <= show_on_both)
+			show = true;
+
+		if ( show ) {
+			w->widget[icon].type = WWT_IMGBTN;
+			w->widget[icon].left = x;
+			x += button_width;
+			w->widget[icon].right = w->widget[icon].left + icon_size - 1;
+		} else {
+			w->widget[icon].type = WWT_EMPTY;
+		}
+	}
+
+	w->widget[27].data = _switched_bar?SPR_IMG_TERRAFORM_UP:SPR_IMG_TERRAFORM_DOWN;
+	w->widget[27].type = WWT_PUSHIMGBTN;
+	w->widget[27].color = 15;
+}
+
 /* --- Toolbar handling for the 'normal' case */
 
 typedef void ToolbarButtonProc(Window *w);
@@ -647,6 +741,7 @@
 	ToolbarMusicClick,
 	ToolbarNewspaperClick,
 	ToolbarHelpClick,
+	ToolbarSwitchClick,
 };
 
 static void MainToolbarWndProc(Window *w, WindowEvent *e)
@@ -740,30 +835,10 @@
 			break;
 
 		case WE_RESIZE: {
-			/* There are 27 buttons plus some spacings if the space allows it */
-			uint button_width;
-			uint spacing;
-			if (w->width >= 27 * 22) {
-				button_width = 22;
-				spacing = w->width - (27 * button_width);
-			} else {
-				button_width = w->width / 27;
-				spacing = 0;
-			}
-			uint extra_spacing_at[] = { 4, 8, 13, 17, 19, 24, 0 };
-
-			for (uint i = 0, x = 0, j = 0; i < 27; i++) {
-				if (extra_spacing_at[j] == i) {
-					j++;
-					uint add = spacing / (lengthof(extra_spacing_at) - j);
-					spacing -= add;
-					x += add;
-				}
-
-				w->widget[i].left = x;
-				x += (spacing != 0) ? button_width : (w->width - x) / (27 - i);
-				w->widget[i].right = x - 1;
-			}
+			if (w->width <= 20 * 22)
+				SplitToolbar(w);
+			else
+				ResizeToolbar(w);
 		} break;
 
 		case WE_TIMEOUT:
@@ -815,6 +890,7 @@
 {     WWT_IMGBTN,   RESIZE_NONE,    14,     0,     0,     0,    21, SPR_IMG_MUSIC,           STR_01D4_SHOW_SOUND_MUSIC_WINDOW},
 {     WWT_IMGBTN,   RESIZE_NONE,    14,     0,     0,     0,    21, SPR_IMG_MESSAGES,        STR_0203_SHOW_LAST_MESSAGE_NEWS},
 {     WWT_IMGBTN,   RESIZE_NONE,    14,     0,     0,     0,    21, SPR_IMG_QUERY,           STR_0186_LAND_BLOCK_INFORMATION},
+{     WWT_EMPTY,    RESIZE_NONE,    14,     0,     0,     0,    21, SPR_IMG_TERRAFORM_UP,    STR_EMPTY}, // switch toolbar button. only active when toolbar has been split
 {   WIDGETS_END},
 };