Add "Freight" type to vehicle list cargo type filter

src/lang/english.txt

@@ -3995,6 +3995,8 @@ STR_PURCHASE_INFO_MAX_TE                                        :{BLACK}Max. Tra
 STR_PURCHASE_INFO_AIRCRAFT_RANGE                                :{BLACK}Range: {GOLD}{COMMA} tiles
 STR_PURCHASE_INFO_AIRCRAFT_TYPE                                 :{BLACK}Aircraft type: {GOLD}{STRING}
 
+STR_CARGO_TYPE_FREIGHT                                          :Freight
+
 STR_BUY_VEHICLE_TRAIN_LIST_TOOLTIP                              :{BLACK}Train vehicle selection list. Click on vehicle for information. Ctrl+Click for toggling hiding of the vehicle type
 STR_BUY_VEHICLE_ROAD_VEHICLE_LIST_TOOLTIP                       :{BLACK}Road vehicle selection list. Click on vehicle for information. Ctrl+Click for toggling hiding of the vehicle type
 STR_BUY_VEHICLE_SHIP_LIST_TOOLTIP                               :{BLACK}Ship selection list. Click on ship for information. Ctrl+Click for toggling hiding of the ship type

src/vehicle_gui.cpp

@@ -162,6 +162,18 @@ static bool CDECL CargoFilter(const Vehicle * const *vid, const CargoID cid)
 			}
 		}
 		return true;
+	} else if (cid == BaseVehicleListWindow::CF_FREIGHT) {
+		bool have_capacity = false;
+		for (const Vehicle *w = (*vid); w != NULL; w = w->Next()) {
+			if (w->cargo_cap) {
+				if (IsCargoInClass(w->cargo_type, CC_PASSENGERS)) {
+					return false;
+				} else {
+					have_capacity = true;
+				}
+			}
+		}
+		return have_capacity;
 	} else {
 		for (const Vehicle *w = (*vid); w != NULL; w = w->Next()) {
 			if (w->cargo_cap > 0 && w->cargo_type == cid) {
@@ -199,6 +211,11 @@ void BaseVehicleListWindow::SetCargoFilterArray()
 	this->cargo_filter_criteria = filter_items;
 	filter_items++;
 
+	/* Add item for freight (i.e. vehicles with cargo capacity and with no passenger capacity) */
+	this->cargo_filter[filter_items] = CF_FREIGHT;
+	this->cargo_filter_texts[filter_items] = STR_CARGO_TYPE_FREIGHT;
+	filter_items++;
+
 	/* Add item for vehicles not carrying anything, e.g. train engines.
 	* This could also be useful for eyecandy vehicles of other types, but is likely too confusing for joe, */
 	this->cargo_filter[filter_items] = CF_NONE;

src/vehicle_gui_base.h

@@ -32,10 +32,11 @@ struct BaseVehicleListWindow : public Window {
 	enum CargoFilterSpecialType {
 		CF_ANY = CT_NO_REFIT,                   ///< Show all vehicles independent of carried cargo (i.e. no filtering)
 		CF_NONE = CT_INVALID,                   ///< Show only vehicles which do not carry cargo (e.g. train engines)
+		CF_FREIGHT = CT_AUTO_REFIT,             ///< Show only vehicles which carry any freight (non-passenger) cargo
 	};
 
-	CargoID cargo_filter[NUM_CARGO + 2];        ///< Available cargo filters; CargoID or CF_ANY or CF_NONE
-	StringID cargo_filter_texts[NUM_CARGO + 3]; ///< Texts for filter_cargo, terminated by INVALID_STRING_ID
+	CargoID cargo_filter[NUM_CARGO + 3];        ///< Available cargo filters; CargoID or CF_ANY or CF_NONE
+	StringID cargo_filter_texts[NUM_CARGO + 4]; ///< Texts for filter_cargo, terminated by INVALID_STRING_ID
 	byte cargo_filter_criteria;                 ///< Selected cargo filter
 
 	enum ActionDropdownItem {