Feature: Colourblind-friendly linkgraph colour scheme

src/lang/english.txt

@@ -1739,6 +1739,11 @@ STR_CONFIG_SETTING_DEMAND_SIZE_HELPTEXT                         :Setting this to
 STR_CONFIG_SETTING_SHORT_PATH_SATURATION                        :Saturation of short paths before using high-capacity paths: {STRING2}
 STR_CONFIG_SETTING_SHORT_PATH_SATURATION_HELPTEXT               :Frequently there are multiple paths between two given stations. Cargodist will saturate the shortest path first, then use the second shortest path until that is saturated and so on. Saturation is determined by an estimation of capacity and planned usage. Once it has saturated all paths, if there is still demand left, it will overload all paths, prefering the ones with high capacity. Most of the time the algorithm will not estimate the capacity accurately, though. This setting allows you to specify up to which percentage a shorter path must be saturated in the first pass before choosing the next longer one. Set it to less than 100% to avoid overcrowded stations in case of overestimated capacity.
 
+STR_CONFIG_SETTING_LINKGRAPH_COLOURS                            :Cargo flow overlay colours: {STRING2}
+STR_CONFIG_SETTING_LINKGRAPH_COLOURS_HELPTEXT                   :Set the colour scheme used for the cargo flow overlay.
+STR_CONFIG_SETTING_LINKGRAPH_COLOURS_GREEN_TO_RED               :Green to red (original)
+STR_CONFIG_SETTING_LINKGRAPH_COLOURS_BLUE_TO_RED                :Blue to red
+
 STR_CONFIG_SETTING_LOCALISATION_UNITS_VELOCITY                  :Speed units: {STRING2}
 STR_CONFIG_SETTING_LOCALISATION_UNITS_VELOCITY_HELPTEXT         :Whenever a speed is shown in the user interface, show it in the selected units
 STR_CONFIG_SETTING_LOCALISATION_UNITS_VELOCITY_IMPERIAL         :Imperial (mph)

src/linkgraph/linkgraph_gui.cpp

@@ -26,10 +26,17 @@
  * Colours for the various "load" states of links. Ordered from "unused" to
  * "overloaded".
  */
-const uint8 LinkGraphOverlay::LINK_COLOURS[] = {
-	0x0f, 0xd1, 0xd0, 0x57,
-	0x55, 0x53, 0xbf, 0xbd,
-	0xba, 0xb9, 0xb7, 0xb5
+const uint8 LinkGraphOverlay::LINK_COLOURS[][12] = {
+	{
+		0x0f, 0xd1, 0xd0, 0x57,
+		0x55, 0x53, 0xbf, 0xbd,
+		0xba, 0xb9, 0xb7, 0xb5
+	},
+	{
+		0x07, 0xc6, 0xc9, 0xcb,
+		0xcd, 0x99, 0x44, 0xbe,
+		0xbb, 0xb9, 0xb7, 0xb5
+	}
 };
 
 /**
@@ -271,7 +278,7 @@ void LinkGraphOverlay::DrawLinks(const DrawPixelInfo *dpi) const
 void LinkGraphOverlay::DrawContent(Point pta, Point ptb, const LinkProperties &cargo) const
 {
 	uint usage_or_plan = std::min(cargo.capacity * 2 + 1, std::max(cargo.usage, cargo.planned));
-	int colour = LinkGraphOverlay::LINK_COLOURS[usage_or_plan * lengthof(LinkGraphOverlay::LINK_COLOURS) / (cargo.capacity * 2 + 2)];
+	int colour = LinkGraphOverlay::LINK_COLOURS[_settings_client.gui.linkgraph_colours][usage_or_plan * lengthof(LinkGraphOverlay::LINK_COLOURS[0]) / (cargo.capacity * 2 + 2)];
 	int dash = cargo.shared ? this->scale * 4 : 0;
 
 	/* Move line a bit 90° against its dominant direction to prevent it from
@@ -379,7 +386,7 @@ NWidgetBase *MakeCompanyButtonRowsLinkGraphGUI(int *biggest_index)
 NWidgetBase *MakeSaturationLegendLinkGraphGUI(int *biggest_index)
 {
 	NWidgetVertical *panel = new NWidgetVertical(NC_EQUALSIZE);
-	for (uint i = 0; i < lengthof(LinkGraphOverlay::LINK_COLOURS); ++i) {
+	for (uint i = 0; i < lengthof(LinkGraphOverlay::LINK_COLOURS[0]); ++i) {
 		NWidgetBackground * wid = new NWidgetBackground(WWT_PANEL, COLOUR_DARK_GREEN, i + WID_LGL_SATURATION_FIRST);
 		wid->SetMinimalSize(50, 0);
 		wid->SetMinimalTextLines(1, 0, FS_SMALL);
@@ -456,7 +463,7 @@ static const NWidgetPart _nested_linkgraph_legend_widgets[] = {
 };
 
 static_assert(WID_LGL_SATURATION_LAST - WID_LGL_SATURATION_FIRST ==
-		lengthof(LinkGraphOverlay::LINK_COLOURS) - 1);
+		lengthof(LinkGraphOverlay::LINK_COLOURS[0]) - 1);
 
 static WindowDesc _linkgraph_legend_desc(
 	WDP_AUTO, "toolbar_linkgraph", 0, 0,
@@ -538,7 +545,8 @@ void LinkGraphLegendWindow::DrawWidget(const Rect &r, int widget) const
 		DrawCompanyIcon(cid, (r.left + r.right + 1 - sprite_size.width) / 2, (r.top + r.bottom + 1 - sprite_size.height) / 2);
 	}
 	if (IsInsideMM(widget, WID_LGL_SATURATION_FIRST, WID_LGL_SATURATION_LAST + 1)) {
-		GfxFillRect(r.left + 1, r.top + 1, r.right - 1, r.bottom - 1, LinkGraphOverlay::LINK_COLOURS[widget - WID_LGL_SATURATION_FIRST]);
+		uint8 colour = LinkGraphOverlay::LINK_COLOURS[_settings_client.gui.linkgraph_colours][widget - WID_LGL_SATURATION_FIRST];
+		GfxFillRect(r.left + 1, r.top + 1, r.right - 1, r.bottom - 1, colour);
 		StringID str = STR_NULL;
 		if (widget == WID_LGL_SATURATION_FIRST) {
 			str = STR_LINKGRAPH_LEGEND_UNUSED;
@@ -547,7 +555,9 @@ void LinkGraphLegendWindow::DrawWidget(const Rect &r, int widget) const
 		} else if (widget == (WID_LGL_SATURATION_LAST + WID_LGL_SATURATION_FIRST) / 2) {
 			str = STR_LINKGRAPH_LEGEND_SATURATED;
 		}
-		if (str != STR_NULL) DrawString(r.left, r.right, (r.top + r.bottom + 1 - FONT_HEIGHT_SMALL) / 2, str, TC_FROMSTRING, SA_HOR_CENTER);
+		if (str != STR_NULL) {
+			DrawString(r.left, r.right, (r.top + r.bottom + 1 - FONT_HEIGHT_SMALL) / 2, str, GetContrastColour(colour) | TC_FORCED, SA_HOR_CENTER);
+		}
 	}
 	if (IsInsideMM(widget, WID_LGL_CARGO_FIRST, WID_LGL_CARGO_LAST + 1)) {
 		if (this->IsWidgetDisabled(widget)) return;

src/linkgraph/linkgraph_gui.h

@@ -40,7 +40,7 @@ class LinkGraphOverlay {
 	typedef std::map<StationID, StationLinkMap> LinkMap;
 	typedef std::vector<std::pair<StationID, uint> > StationSupplyList;
 
-	static const uint8 LINK_COLOURS[];
+	static const uint8 LINK_COLOURS[][12];
 
 	/**
 	 * Create a link graph overlay for the specified window.

src/settings_gui.cpp

@@ -1570,6 +1570,7 @@ static SettingsContainer &GetSettingsTree()
 			graphics->Add(new SettingEntry("gui.zoom_max"));
 			graphics->Add(new SettingEntry("gui.sprite_zoom_min"));
 			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_table.cpp

@@ -103,6 +103,16 @@ static void RedrawSmallmap(int32 new_value)
 	SetWindowClassesDirty(WC_SMALLMAP);
 }
 
+/**
+* Redraw the linkgraph after a colour scheme change.
+* @param new_value Callback parameter.
+*/
+static void UpdateLinkgraphColours(int32 new_value)
+{
+	BuildLinkStatsLegend();
+	MarkWholeScreenDirty();
+}
+
 static void StationSpreadChanged(int32 p1)
 {
 	InvalidateWindowData(WC_SELECT_STATION, 0);

src/settings_type.h

@@ -114,6 +114,7 @@ struct GUISettings {
 	uint16 hover_delay_ms;                   ///< time required to activate a hover event, in milliseconds
 	bool   link_terraform_toolbar;           ///< display terraform toolbar when displaying rail, road, water and airport toolbars
 	uint8  smallmap_land_colour;             ///< colour used for land and heightmap at the smallmap
+	uint8  linkgraph_colours;                ///< Colour scheme used in the linkgraph overlay.
 	uint8  scroll_mode;                      ///< viewport scroll mode
 	bool   smooth_scroll;                    ///< smooth scroll viewports
 	bool   measure_tooltip;                  ///< show a permanent tooltip when dragging tools

src/smallmap_gui.cpp

@@ -216,7 +216,7 @@ void BuildLinkStatsLegend()
 
 	for (; i < _smallmap_cargo_count + lengthof(_linkstat_colours_in_legenda); ++i) {
 		_legend_linkstats[i].legend = STR_EMPTY;
-		_legend_linkstats[i].colour = LinkGraphOverlay::LINK_COLOURS[_linkstat_colours_in_legenda[i - _smallmap_cargo_count]];
+		_legend_linkstats[i].colour = LinkGraphOverlay::LINK_COLOURS[_settings_client.gui.linkgraph_colours][_linkstat_colours_in_legenda[i - _smallmap_cargo_count]];
 		_legend_linkstats[i].show_on_map = true;
 	}
 

src/table/settings/gui_settings.ini

@@ -15,6 +15,7 @@ static void InvalidateCompanyLiveryWindow(int32 new_value);
 static void InvalidateNewGRFChangeWindows(int32 new_value);
 static void ZoomMinMaxChanged(int32 new_value);
 static void SpriteZoomMinChanged(int32 new_value);
+static void UpdateLinkgraphColours(int32 new_value);
 
 static std::initializer_list<const char*> _autosave_interval{"off", "monthly", "quarterly", "half year", "yearly"};
 static std::initializer_list<const char*> _osk_activation{"disabled", "double", "single", "immediately"};
@@ -313,6 +314,19 @@ strhelp  = STR_CONFIG_SETTING_SMALLMAP_LAND_COLOUR_HELPTEXT
 strval   = STR_CONFIG_SETTING_SMALLMAP_LAND_COLOUR_GREEN
 post_cb  = RedrawSmallmap
 
+[SDTC_VAR]
+var      = gui.linkgraph_colours
+type     = SLE_UINT8
+flags    = SF_NOT_IN_SAVE | SF_NO_NETWORK_SYNC | SF_GUI_DROPDOWN
+def      = 1
+min      = 0
+max      = 1
+str      = STR_CONFIG_SETTING_LINKGRAPH_COLOURS
+strhelp  = STR_CONFIG_SETTING_LINKGRAPH_COLOURS_HELPTEXT
+strval   = STR_CONFIG_SETTING_LINKGRAPH_COLOURS_GREEN_TO_RED
+post_cb  = UpdateLinkgraphColours
+cat      = SC_BASIC
+
 [SDTC_VAR]
 var      = gui.liveries
 type     = SLE_UINT8