Codefix: DrawEngineList does not accept EngineID.

Replace min/max parameters of DrawEngineList with scrollbar reference, and use iterators instead of indices.

src/autoreplace_gui.cpp

@@ -33,7 +33,7 @@
 
 #include "safeguards.h"
 
-void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_list, uint16_t min, uint16_t max, EngineID selected_id, bool show_count, GroupID selected_group);
+void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_list, const Scrollbar &sb, EngineID selected_id, bool show_count, GroupID selected_group);
 
 static bool EngineNumberSorter(const GUIEngineListItem &a, const GUIEngineListItem &b)
 {
@@ -487,11 +487,9 @@ public:
 			case WID_RV_LEFT_MATRIX:
 			case WID_RV_RIGHT_MATRIX: {
 				int side = (widget == WID_RV_LEFT_MATRIX) ? 0 : 1;
-				EngineID start  = static_cast<EngineID>(this->vscroll[side]->GetPosition()); // what is the offset for the start (scrolling)
-				EngineID end    = static_cast<EngineID>(std::min<size_t>(this->vscroll[side]->GetCapacity() + start, this->engines[side].size()));
 
 				/* Do the actual drawing */
-				DrawEngineList((VehicleType)this->window_number, r, this->engines[side], start, end, this->sel_engine[side], side == 0, this->sel_group);
+				DrawEngineList((VehicleType)this->window_number, r, this->engines[side], *this->vscroll[side], this->sel_engine[side], side == 0, this->sel_group);
 				break;
 			}
 		}

src/build_vehicle_gui.cpp

@@ -998,18 +998,16 @@ int DrawVehiclePurchaseInfo(int left, int right, int y, EngineID engine_number,
  * @param type Type of vehicle (VEH_*)
  * @param r The Rect of the list
  * @param eng_list What engines to draw
- * @param min where to start in the list
+ * @param sb Scrollbar of list.
- * @param max where in the list to end
  * @param selected_id what engine to highlight as selected, if any
  * @param show_count Whether to show the amount of engines or not
  * @param selected_group the group to list the engines of
  */
-void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_list, uint16_t min, uint16_t max, EngineID selected_id, bool show_count, GroupID selected_group)
+void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_list, const Scrollbar &sb, EngineID selected_id, bool show_count, GroupID selected_group)
 {
 	static const int sprite_y_offsets[] = { -1, -1, -2, -2 };
 
-	/* Obligatory sanity checks! */
+	auto [first, last] = sb.GetVisibleRangeIterators(eng_list);
-	assert(max <= eng_list.size());
 
 	bool rtl = _current_text_dir == TD_RTL;
 	int step_size = GetEngineListHeight(type);
@@ -1028,9 +1026,8 @@ void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_li
 		replace_icon = GetSpriteSize(SPR_GROUP_REPLACE_ACTIVE);
 
 		uint biggest_num_engines = 0;
-		for (auto i = min; i < max; i++) {
+		for (auto it = first; it != last; ++it) {
-			const auto &item = eng_list[i];
+			const uint num_engines = GetGroupNumEngines(_local_company, selected_group, it->engine_id);
-			const uint num_engines = GetGroupNumEngines(_local_company, selected_group, item.engine_id);
 			biggest_num_engines = std::max(biggest_num_engines, num_engines);
 		}
 
@@ -1048,8 +1045,8 @@ void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_li
 	int replace_icon_y_offset = (ir.Height() - replace_icon.height) / 2;
 
 	int y = ir.top;
-	for (; min < max; min++, y += step_size) {
+	for (auto it = first; it != last; ++it) {
-		const auto &item = eng_list[min];
+		const auto &item = *it;
 		uint indent       = item.indent * WidgetDimensions::scaled.hsep_indent;
 		bool has_variants = (item.flags & EngineDisplayFlags::HasVariants) != EngineDisplayFlags::None;
 		bool is_folded    = (item.flags & EngineDisplayFlags::IsFolded)    != EngineDisplayFlags::None;
@@ -1085,10 +1082,11 @@ void DrawEngineList(VehicleType type, const Rect &r, const GUIEngineList &eng_li
 			/* Draw tree lines */
 			Rect fr = ir.Indent(indent - WidgetDimensions::scaled.hsep_indent, rtl).WithWidth(circle_width, rtl);
 			int ycenter = y + normal_text_y_offset + GetCharacterHeight(FS_NORMAL) / 2;
-			bool continues = (min + 1U) < eng_list.size() && eng_list[min + 1].indent == item.indent;
+			bool continues = std::next(it) != std::end(eng_list) && std::next(it)->indent == item.indent;
 			GfxDrawLine(fr.left + circle_width / 2, y - WidgetDimensions::scaled.matrix.top, fr.left + circle_width / 2, continues ? y - WidgetDimensions::scaled.matrix.top + step_size - 1 : ycenter, linecolour, WidgetDimensions::scaled.fullbevel.top);
 			GfxDrawLine(fr.left + circle_width / 2, ycenter, fr.right, ycenter, linecolour, WidgetDimensions::scaled.fullbevel.top);
 		}
+		y += step_size;
 	}
 }
 
@@ -1791,8 +1789,7 @@ struct BuildVehicleWindow : Window {
 					this->vehicle_type,
 					r,
 					this->eng_list,
-					this->vscroll->GetPosition(),
+					*this->vscroll,
-					static_cast<uint16_t>(std::min<size_t>(this->vscroll->GetPosition() + this->vscroll->GetCapacity(), this->eng_list.size())),
 					this->sel_engine,
 					false,
 					DEFAULT_GROUP