Allow planting trees on diagonal areas

src/tree_cmd.cpp

@@ -538,7 +538,9 @@ void GenerateTrees()
  * Plant a tree.
  * @param tile end tile of area-drag
  * @param flags type of operation
- * @param p1 tree type, TREE_INVALID means random.
+ * @param p1 various bitstuffed data.
+ * - p1 = (bit 0 -  7) - tree type, TREE_INVALID means random.
+ * - p1 = (bit      8) - whether to use the Orthogonal (0) or Diagonal (1) iterator.
  * @param p2 start tile of area-drag of tree plantation
  * @param text unused
  * @return the cost of this operation or an error
@@ -556,8 +558,9 @@ CommandCost CmdPlantTree(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 	Company *c = (_game_mode != GM_EDITOR) ? Company::GetIfValid(_current_company) : nullptr;
 	int limit = (c == nullptr ? INT32_MAX : GB(c->tree_limit, 16, 16));
 
-	TileArea ta(tile, p2);
-	for (TileIndex tile : ta) {
+	OrthogonalOrDiagonalTileIterator iter(tile, p2, HasBit(p1, 8));
+	for (; *iter != INVALID_TILE; ++iter) {
+		TileIndex tile = *iter;
 		switch (GetTileType(tile)) {
 			case MP_TREES: {
 				bool grow_existing_tree_instead = false;

src/tree_gui.cpp

@@ -90,7 +90,7 @@ class BuildTreesWindow : public Window
 		if (this->tree_to_plant >= 0) {
 			/* Activate placement */
 			if (_settings_client.sound.confirm) SndPlayFx(SND_15_BEEP);
-			SetObjectToPlace(SPR_CURSOR_TREE, PAL_NONE, HT_RECT, this->window_class, this->window_number);
+			SetObjectToPlace(SPR_CURSOR_TREE, PAL_NONE, HT_RECT | HT_DIAGONAL, this->window_class, this->window_number);
 			this->tree_to_plant = current_tree; // SetObjectToPlace may call ResetObjectToPlace which may reset tree_to_plant to -1
 		} else {
 			/* Deactivate placement */
@@ -234,7 +234,7 @@ public:
 	void OnPlaceMouseUp(ViewportPlaceMethod select_method, ViewportDragDropSelectionProcess select_proc, Point pt, TileIndex start_tile, TileIndex end_tile) override
 	{
 		if (_game_mode != GM_EDITOR && this->mode == PM_NORMAL && pt.x != -1 && select_proc == DDSP_PLANT_TREES) {
-			DoCommandP(end_tile, this->tree_to_plant, start_tile, CMD_PLANT_TREE | CMD_MSG(STR_ERROR_CAN_T_PLANT_TREE_HERE));
+			DoCommandP(end_tile, this->tree_to_plant | ((_ctrl_pressed ? 1 : 0) << 8), start_tile, CMD_PLANT_TREE | CMD_MSG(STR_ERROR_CAN_T_PLANT_TREE_HERE));
 		}
 	}