Add: Set the tree line directly in Scenario Editor

src/lang/english.txt

@@ -2979,11 +2979,12 @@ STR_OBJECT_BUILD_SIZE                                           :{BLACK}Size: {G
 STR_OBJECT_CLASS_LTHS                                           :Lighthouses
 STR_OBJECT_CLASS_TRNS                                           :Transmitters
 
-# Tree planting window (last eight for SE only)
+# Tree planting window (in-game and Scenario Editor)
 STR_PLANT_TREE_CAPTION                                          :{WHITE}Trees
 STR_PLANT_TREE_TOOLTIP                                          :{BLACK}Select tree type to plant. If the tile already has a tree, this will add more trees of mixed types independent of the selected type
 STR_TREES_RANDOM_TYPE                                           :{BLACK}Trees of random type
 STR_TREES_RANDOM_TYPE_TOOLTIP                                   :{BLACK}Place trees of random type. Ctrl+Click+Drag to select the area diagonally. Also press Shift to show cost estimate only
+# Tree planting window (Scenario Editor only)
 STR_TREES_RANDOM_TREES_BUTTON                                   :{BLACK}Random Trees
 STR_TREES_RANDOM_TREES_TOOLTIP                                  :{BLACK}Plant trees randomly throughout the landscape
 STR_TREES_MODE_NORMAL_BUTTON                                    :{BLACK}Normal
@@ -2992,6 +2993,10 @@ STR_TREES_MODE_FOREST_SM_BUTTON                                 :{BLACK}Grove
 STR_TREES_MODE_FOREST_SM_TOOLTIP                                :{BLACK}Plant small forests by dragging over the landscape
 STR_TREES_MODE_FOREST_LG_BUTTON                                 :{BLACK}Forest
 STR_TREES_MODE_FOREST_LG_TOOLTIP                                :{BLACK}Plant large forests by dragging over the landscape
+STR_BUILD_TREES_TREELINE_LABEL                                  :{BLACK}Tree line height:
+STR_BUILD_TREES_TREELINE_TOOLTIP                                :{BLACK}Choose the tree line height. Above this level, trees will not grow
+STR_BUILD_TREES_TREELINE_DECREASE_TOOLTIP                       :{BLACK}Decrease the tree line height
+STR_BUILD_TREES_TREELINE_INCREASE_TOOLTIP                       :{BLACK}Increase the tree line height
 
 # Land generation window (SE)
 STR_TERRAFORM_TOOLBAR_LAND_GENERATION_CAPTION                   :{WHITE}Land Generation

src/tree_gui.cpp

@@ -149,6 +149,12 @@ public:
 		if (_game_mode != GM_EDITOR) {
 			this->GetWidget<NWidgetStacked>(WID_BT_SE_PANE)->SetDisplayedPlane(SZSP_HORIZONTAL);
 		}
+
+		/* Only show tree line in subarctic climate. */
+		if (_settings_game.game_creation.landscape != LT_ARCTIC) {
+			this->GetWidget<NWidgetStacked>(WID_BT_TREELINE_PANE)->SetDisplayedPlane(SZSP_HORIZONTAL);
+		}
+
 		this->FinishInitNested(window_number);
 	}
 
@@ -162,6 +168,15 @@ public:
 		}
 	}
 
+	void SetStringParameters(WidgetID widget) const override
+	{
+		switch (widget) {
+			case WID_BT_TREELINE_VALUE:
+				SetDParam(0, _settings_game.game_creation.tree_line_height);
+				break;
+		}
+	}
+
 	void DrawWidget(const Rect &r, WidgetID widget) const override
 	{
 		if (widget >= WID_BT_TYPE_BUTTON_FIRST) {
@@ -202,6 +217,18 @@ public:
 				this->UpdateMode();
 				break;
 
+			case WID_BT_TREELINE_DECREASE:
+				assert(_game_mode == GM_EDITOR);
+				_settings_game.game_creation.tree_line_height = Clamp(_settings_game.game_creation.tree_line_height - 1, 0, 100);
+				this->InvalidateData();
+				break;
+
+			case WID_BT_TREELINE_INCREASE:
+				assert(_game_mode == GM_EDITOR);
+				_settings_game.game_creation.tree_line_height = Clamp(_settings_game.game_creation.tree_line_height + 1, 0, 100);
+				this->InvalidateData();
+				break;
+
 			default:
 				if (widget >= WID_BT_TYPE_BUTTON_FIRST) {
 					const int index = widget - WID_BT_TYPE_BUTTON_FIRST;
@@ -304,6 +331,16 @@ static constexpr NWidgetPart _nested_build_trees_widgets[] = {
 						NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_BT_MODE_FOREST_LG), SetFill(1, 0), SetDataTip(STR_TREES_MODE_FOREST_LG_BUTTON, STR_TREES_MODE_FOREST_LG_TOOLTIP),
 					EndContainer(),
 					NWidget(WWT_PUSHTXTBTN, COLOUR_GREY, WID_BT_MANY_RANDOM), SetDataTip(STR_TREES_RANDOM_TREES_BUTTON, STR_TREES_RANDOM_TREES_TOOLTIP),
+					NWidget(NWID_SELECTION, INVALID_COLOUR, WID_BT_TREELINE_PANE),
+						NWidget(NWID_HORIZONTAL), SetPadding(2), SetPIP(0, 1, 0),
+							NWidget(WWT_LABEL, COLOUR_DARK_GREEN, WID_BT_TREELINE_LABEL), SetDataTip(STR_BUILD_TREES_TREELINE_LABEL, STR_BUILD_TREES_TREELINE_TOOLTIP), SetFill(1, 1),
+							NWidget(WWT_LABEL, COLOUR_DARK_GREEN, WID_BT_TREELINE_VALUE), SetDataTip(STR_JUST_INT, STR_BUILD_TREES_TREELINE_TOOLTIP), SetTextStyle(TC_ORANGE), SetFill(1, 1),
+							NWidget(NWID_HORIZONTAL),
+								NWidget(WWT_PUSHARROWBTN, COLOUR_GREY, WID_BT_TREELINE_DECREASE), SetMinimalSize(9, 12), SetDataTip(AWV_DECREASE, STR_BUILD_TREES_TREELINE_DECREASE_TOOLTIP),
+								NWidget(WWT_PUSHARROWBTN, COLOUR_GREY, WID_BT_TREELINE_INCREASE), SetMinimalSize(9, 12), SetDataTip(AWV_INCREASE, STR_BUILD_TREES_TREELINE_INCREASE_TOOLTIP),
+							EndContainer(),
+						EndContainer(),
+					EndContainer(),
 				EndContainer(),
 			EndContainer(),
 		EndContainer(),

src/widgets/tree_widget.h

@@ -18,6 +18,11 @@ enum BuildTreesWidgets : WidgetID {
 	WID_BT_MODE_FOREST_SM,  ///< Select small forest planting mode.
 	WID_BT_MODE_FOREST_LG,  ///< Select large forest planting mode.
 	WID_BT_MANY_RANDOM,     ///< Button to build many random trees.
+	WID_BT_TREELINE_PANE,   ///< Selection pane to show/hide the tree line height, only shown in subarctic climate.
+	WID_BT_TREELINE_LABEL,  ///< Label for the tree line title.
+	WID_BT_TREELINE_VALUE,  ///< Label for the tree line value.
+	WID_BT_TREELINE_DECREASE, ///< Button to decrease the tree line height.
+	WID_BT_TREELINE_INCREASE, ///< Button to increase the tree line height.
 	WID_BT_TYPE_BUTTON_FIRST, ///< First tree type selection button. (This must be last in the enum.)
 };