Add GUI setting for shading trees on slopes in viewports

Deafult on, only for non-map mode
(Slope shading is always on in map mode)

src/lang/english.txt

@@ -1418,6 +1418,9 @@ STR_CONFIG_SETTING_VEHICLE_NAMES_TRADITIONAL                    :Traditional
 STR_CONFIG_SETTING_VEHICLE_NAMES_MODERN                         :Modern
 STR_CONFIG_SETTING_VEHICLE_NAMES_LONG                           :Long
 
+STR_CONFIG_SETTING_SHADED_TREES_ON_SLOPES                       :Shade trees on slopes: {STRING2}
+STR_CONFIG_SETTING_SHADED_TREES_ON_SLOPES_HELPTEXT              :Change brightness of trees drawn on slopes. Improves the look of tree cover in mountainous areas.
+
 STR_CONFIG_SETTING_ADV_SIG_BRIDGE_TUN_MODES                     :Enable signals on bridges/tunnels advanced modes: {STRING2}
 STR_CONFIG_SETTING_ADV_SIG_BRIDGE_TUN_MODES_HELPTEXT            :Enables use of advanced modes of signal simulation on bridges and tunnels. When disabled, bridges/tunnels which are not already in an advanced mode cannot be changed to an advanced mode, however other players may choose to enable this setting and use an advanced mode.
 

src/settings_gui.cpp

@@ -1486,6 +1486,7 @@ static SettingsContainer &GetSettingsTree()
 		{
 			graphics->Add(new SettingEntry("gui.zoom_min"));
 			graphics->Add(new SettingEntry("gui.zoom_max"));
+			graphics->Add(new SettingEntry("gui.shade_trees_on_slopes"));
 			graphics->Add(new SettingEntry("gui.smallmap_land_colour"));
 			graphics->Add(new SettingEntry("gui.linkgraph_colours"));
 			graphics->Add(new SettingEntry("gui.graph_line_thickness"));

src/settings_type.h

@@ -208,6 +208,7 @@ struct GUISettings : public TimeSettings {
 	uint8  linkgraph_colours;                ///< linkgraph overlay colours
 	bool   disable_vehicle_image_update;     ///< Disable NewGRFs from continuously updating vehicle images
 	uint8  vehicle_names;                    ///< Vehicle naming scheme
+	bool   shade_trees_on_slopes;            ///< Shade trees on slopes
 
 	uint16 console_backlog_timeout;          ///< the minimum amount of time items should be in the console backlog before they will be removed in ~3 seconds granularity.
 	uint16 console_backlog_length;           ///< the minimum amount of items in the console backlog before items will be removed.

src/table/settings.ini

@@ -5094,6 +5094,15 @@ strval   = STR_CONFIG_SETTING_VEHICLE_NAMES_TRADITIONAL
 proc     = RedrawScreen
 cat      = SC_BASIC
 
+[SDTC_BOOL]
+var      = gui.shade_trees_on_slopes
+flags    = SLF_NOT_IN_SAVE | SLF_NO_NETWORK_SYNC
+def      = true
+str      = STR_CONFIG_SETTING_SHADED_TREES_ON_SLOPES
+strhelp  = STR_CONFIG_SETTING_SHADED_TREES_ON_SLOPES_HELPTEXT
+proc     = RedrawScreen
+cat      = SC_BASIC
+
 ; For the dedicated build we'll enable dates in logs by default.
 [SDTC_BOOL]
 ifdef    = DEDICATED

src/tree_cmd.cpp

@@ -637,9 +637,19 @@ static void DrawTile_Trees(TileInfo *ti, DrawTileProcParams params)
 	/* put the trees to draw in a list */
 	uint trees = GetTreeCount(ti->tile);
 
+	PaletteID palette_adjust = 0;
+	if (_settings_client.gui.shade_trees_on_slopes && ti->tileh != SLOPE_FLAT) {
+		extern int GetSlopeTreeBrightnessAdjust(Slope slope);
+		int adjust = GetSlopeTreeBrightnessAdjust(ti->tileh);
+		if (adjust != 0) {
+			SetBit(palette_adjust, PALETTE_BRIGHTNESS_MODIFY);
+			SB(palette_adjust, PALETTE_BRIGHTNESS_OFFSET, PALETTE_BRIGHTNESS_WIDTH, adjust & ((1 << PALETTE_BRIGHTNESS_WIDTH) - 1));
+		}
+	}
+
 	for (uint i = 0; i < trees; i++) {
 		SpriteID sprite = s[0].sprite + (i == trees - 1 ? GetTreeGrowth(ti->tile) : 3);
-		PaletteID pal = s[0].pal;
+		PaletteID pal = s[0].pal | palette_adjust;
 
 		te[i].sprite = sprite;
 		te[i].pal    = pal;