(svn r20223) -Codechange: Replace scrolled row calculations by a call to GetScrolledRowFromWidget().

19 files changed, 58 insertions, 134 deletions

diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
index 6acdaa279..e3f4c53bf 100644
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -156,7 +156,7 @@ struct AIListWindow : public Window {
 	{
 		switch (widget) {
 			case AIL_WIDGET_LIST: { // Select one of the AIs
-				int sel = (pt.y - this->GetWidget<NWidgetBase>(AIL_WIDGET_LIST)->pos_y) / this->line_height + this->vscroll.GetPosition() - 1;
+				int sel = this->vscroll.GetScrolledRowFromWidget(pt.y, this, AIL_WIDGET_LIST, 0, this->line_height) - 1;
 				if (sel < (int)this->ai_info_list->size()) {
 					this->selected = sel;
 					this->SetDirty();
@@ -597,7 +597,7 @@ struct AIConfigWindow : public Window {
 			}
 
 			case AIC_WIDGET_LIST: { // Select a slot
-				this->selected_slot = (CompanyID)((pt.y - this->GetWidget<NWidgetBase>(widget)->pos_y) / this->line_height + this->vscroll.GetPosition());
+				this->selected_slot = (CompanyID)this->vscroll.GetScrolledRowFromWidget(pt.y, this, widget, 0, this->line_height);
 				this->InvalidateData();
 				if (click_count > 1 && this->selected_slot != INVALID_COMPANY) ShowAIListWindow((CompanyID)this->selected_slot);
 				break;
diff --git a/src/autoreplace_gui.cpp b/src/autoreplace_gui.cpp
index d4d1cb87f..963721beb 100644
--- a/src/autoreplace_gui.cpp
+++ b/src/autoreplace_gui.cpp
@@ -443,25 +443,27 @@ public:
 
 			case RVW_WIDGET_LEFT_MATRIX:
 			case RVW_WIDGET_RIGHT_MATRIX: {
-				uint i = (pt.y - this->GetWidget<NWidgetBase>(RVW_WIDGET_LEFT_MATRIX)->pos_y) / this->resize.step_height;
-				uint16 click_scroll_pos = widget == RVW_WIDGET_LEFT_MATRIX ? this->vscroll.GetPosition() : this->vscroll2.GetPosition();
-				uint16 click_scroll_cap = widget == RVW_WIDGET_LEFT_MATRIX ? this->vscroll.GetCapacity() : this->vscroll2.GetCapacity();
-				byte click_side         = widget == RVW_WIDGET_LEFT_MATRIX ? 0 : 1;
-				size_t engine_count     = this->engines[click_side].Length();
-
-				if (i < click_scroll_cap) {
-					i += click_scroll_pos;
-					EngineID e = engine_count > i ? this->engines[click_side][i] : INVALID_ENGINE;
-					if (e == this->sel_engine[click_side]) break; // we clicked the one we already selected
-					this->sel_engine[click_side] = e;
-					if (click_side == 0) {
-						this->engines[1].ForceRebuild();
-						this->reset_sel_engine = true;
-					}
-					this->SetDirty();
-					}
-				break;
+				uint i;
+				byte click_side;
+				if (widget == RVW_WIDGET_LEFT_MATRIX) {
+					i = this->vscroll.GetScrolledRowFromWidget(pt.y, this, RVW_WIDGET_LEFT_MATRIX);
+					click_side = 0;
+				} else {
+					i = this->vscroll2.GetScrolledRowFromWidget(pt.y, this, RVW_WIDGET_RIGHT_MATRIX);
+					click_side = 1;
 				}
+				size_t engine_count = this->engines[click_side].Length();
+
+				EngineID e = engine_count > i ? this->engines[click_side][i] : INVALID_ENGINE;
+				if (e == this->sel_engine[click_side]) break; // we clicked the one we already selected
+				this->sel_engine[click_side] = e;
+				if (click_side == 0) {
+					this->engines[1].ForceRebuild();
+					this->reset_sel_engine = true;
+				}
+				this->SetDirty();
+				break;
+			}
 		}
 	}
 
diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
index c11d7554f..5f3e07aab 100644
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -249,13 +249,10 @@ public:
 		switch (widget) {
 			default: break;
 			case BBSW_BRIDGE_LIST: {
-				uint i = ((int)pt.y - this->GetWidget<NWidgetBase>(BBSW_BRIDGE_LIST)->pos_y) / this->resize.step_height;
-				if (i < this->vscroll.GetCapacity()) {
-					i += this->vscroll.GetPosition();
-					if (i < this->bridges->Length()) {
-						this->BuildBridge(i);
-						delete this;
-					}
+				uint i = this->vscroll.GetScrolledRowFromWidget(pt.y, this, BBSW_BRIDGE_LIST);
+				if (i < this->bridges->Length()) {
+					this->BuildBridge(i);
+					delete this;
 				}
 			} break;
 
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
index 69b93ccda..8abd204d8 100644
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -1055,7 +1055,7 @@ struct BuildVehicleWindow : Window {
 				break;
 
 			case BUILD_VEHICLE_WIDGET_LIST: {
-				uint i = (pt.y - this->GetWidget<NWidgetBase>(BUILD_VEHICLE_WIDGET_LIST)->pos_y) / this->resize.step_height + this->vscroll.GetPosition();
+				uint i = this->vscroll.GetScrolledRowFromWidget(pt.y, this, BUILD_VEHICLE_WIDGET_LIST);
 				size_t num_items = this->eng_list.Length();
 				this->sel_engine = (i < num_items) ? this->eng_list[i] : INVALID_ENGINE;
 				this->SetDirty();
diff --git a/src/fios_gui.cpp b/src/fios_gui.cpp
index 8ee17d4bd..7cf6bb3d4 100644
--- a/src/fios_gui.cpp
+++ b/src/fios_gui.cpp
@@ -531,9 +531,8 @@ public:
 				break;
 
 			case SLWW_DRIVES_DIRECTORIES_LIST: { // Click the listbox
-				int y = (pt.y - this->GetWidget<NWidgetBase>(SLWW_DRIVES_DIRECTORIES_LIST)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height;
-
-				if (y < 0 || (y += this->vscroll.GetPosition()) >= this->vscroll.GetCount()) return;
+				int y = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SLWW_DRIVES_DIRECTORIES_LIST, WD_FRAMERECT_TOP);
+				if (y == INT_MAX) return;
 
 				const FiosItem *file = _fios_items.Get(y);
 
diff --git a/src/group_gui.cpp b/src/group_gui.cpp
index c3ddc5812..97e7bce59 100644
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -417,12 +417,7 @@ public:
 				break;
 
 			case GRP_WIDGET_LIST_GROUP: { // Matrix Group
-				uint16 id_g = (pt.y - this->GetWidget<NWidgetBase>(GRP_WIDGET_LIST_GROUP)->pos_y) / (int)this->tiny_step_height;
-
-				if (id_g >= this->vscroll2.GetCapacity()) return;
-
-				id_g += this->vscroll2.GetPosition();
-
+				uint id_g = this->vscroll2.GetScrolledRowFromWidget(pt.y, this, GRP_WIDGET_LIST_GROUP, 0, this->tiny_step_height);
 				if (id_g >= this->groups.Length()) return;
 
 				this->group_sel = this->groups[id_g]->index;
@@ -433,11 +428,7 @@ public:
 			}
 
 			case GRP_WIDGET_LIST_VEHICLE: { // Matrix Vehicle
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(GRP_WIDGET_LIST_VEHICLE)->pos_y) / (int)this->resize.step_height;
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, GRP_WIDGET_LIST_VEHICLE);
 				if (id_v >= this->vehicles.Length()) return; // click out of list bound
 
 				const Vehicle *v = this->vehicles[id_v];
@@ -511,17 +502,11 @@ public:
 				break;
 
 			case GRP_WIDGET_LIST_GROUP: { // Maxtrix group
-				uint16 id_g = (pt.y - this->GetWidget<NWidgetBase>(GRP_WIDGET_LIST_GROUP)->pos_y) / (int)this->tiny_step_height;
 				const VehicleID vindex = this->vehicle_sel;
-
 				this->vehicle_sel = INVALID_VEHICLE;
-
 				this->SetDirty();
 
-				if (id_g >= this->vscroll2.GetCapacity()) return;
-
-				id_g += this->vscroll2.GetPosition();
-
+				uint id_g = this->vscroll2.GetScrolledRowFromWidget(pt.y, this, GRP_WIDGET_LIST_GROUP, 0, this->tiny_step_height);
 				if (id_g >= this->groups.Length()) return;
 
 				DoCommandP(0, this->groups[id_g]->index, vindex, CMD_ADD_VEHICLE_GROUP | CMD_MSG(STR_ERROR_GROUP_CAN_T_ADD_VEHICLE));
@@ -529,17 +514,11 @@ public:
 			}
 
 			case GRP_WIDGET_LIST_VEHICLE: { // Maxtrix vehicle
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(GRP_WIDGET_LIST_VEHICLE)->pos_y) / (int)this->resize.step_height;
 				const VehicleID vindex = this->vehicle_sel;
-
 				this->vehicle_sel = INVALID_VEHICLE;
-
 				this->SetDirty();
 
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, GRP_WIDGET_LIST_VEHICLE);
 				if (id_v >= this->vehicles.Length()) return; // click out of list bound
 
 				const Vehicle *v = this->vehicles[id_v];
diff --git a/src/industry_gui.cpp b/src/industry_gui.cpp
index 50e6b8be4..13cb0b92f 100644
--- a/src/industry_gui.cpp
+++ b/src/industry_gui.cpp
@@ -459,9 +459,8 @@ public:
 		switch (widget) {
 			case DPIW_MATRIX_WIDGET: {
 				const IndustrySpec *indsp;
-				int y = (pt.y - this->GetWidget<NWidgetBase>(DPIW_MATRIX_WIDGET)->pos_y) / this->resize.step_height + this->vscroll.GetPosition();
-
-				if (y >= 0 && y < count) { // Is it within the boundaries of available data?
+				int y = this->vscroll.GetScrolledRowFromWidget(pt.y, this, DPIW_MATRIX_WIDGET);
+				if (y < this->count) { // Is it within the boundaries of available data?
 					this->selected_index = y;
 					this->selected_type = this->index[y];
 					indsp = (this->selected_type == INVALID_INDUSTRYTYPE) ? NULL : GetIndustrySpec(this->selected_type);
@@ -1194,11 +1193,7 @@ public:
 				break;
 
 			case IDW_INDUSTRY_LIST: {
-				int y = (pt.y - this->GetWidget<NWidgetBase>(widget)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height;
-				uint16 p;
-
-				if (!IsInsideMM(y, 0, this->vscroll.GetCapacity())) return;
-				p = y + this->vscroll.GetPosition();
+				uint p = this->vscroll.GetScrolledRowFromWidget(pt.y, this, IDW_INDUSTRY_LIST, WD_FRAMERECT_TOP);
 				if (p < this->industries.Length()) {
 					if (_ctrl_pressed) {
 						ShowExtraViewPortWindow(this->industries[p]->location.tile);
diff --git a/src/network/network_content_gui.cpp b/src/network/network_content_gui.cpp
index 78a589558..e3baf41cb 100644
--- a/src/network/network_content_gui.cpp
+++ b/src/network/network_content_gui.cpp
@@ -590,11 +590,7 @@ public:
 	{
 		switch (widget) {
 			case NCLWW_MATRIX: {
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(NCLWW_MATRIX)->pos_y) / this->resize.step_height;
-
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, NCLWW_MATRIX);
 				if (id_v >= this->content.Length()) return; // click out of bounds
 
 				this->selected = *this->content.Get(id_v);
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
index d0e7a49ce..d7a03a99b 100644
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -689,11 +689,7 @@ public:
 				break;
 
 			case NGWW_MATRIX: { // Matrix to show networkgames
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(NGWW_MATRIX)->pos_y) / this->resize.step_height;
-
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, NGWW_MATRIX);
 				this->server = (id_v < this->servers.Length()) ? this->servers[id_v] : NULL;
 				this->list_pos = (server == NULL) ? SLP_INVALID : id_v;
 				this->SetDirty();
@@ -1170,9 +1166,7 @@ struct NetworkStartServerWindow : public QueryStringBaseWindow {
 				break;
 
 			case NSSW_SELMAP: { // Select map
-				int y = (pt.y - this->GetWidget<NWidgetBase>(NSSW_SELMAP)->pos_y - WD_FRAMERECT_TOP) / FONT_HEIGHT_NORMAL;
-
-				y += this->vscroll.GetPosition();
+				int y = this->vscroll.GetScrolledRowFromWidget(pt.y, this, NSSW_SELMAP, WD_FRAMERECT_TOP, FONT_HEIGHT_NORMAL);
 				if (y >= this->vscroll.GetCount()) return;
 
 				this->map = (y == 0) ? NULL : _fios_items.Get(y - 1);
@@ -1631,11 +1625,7 @@ struct NetworkLobbyWindow : public Window {
 				break;
 
 			case NLWW_MATRIX: { // Company list
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(NLWW_MATRIX)->pos_y) / this->resize.step_height;
-
-				if (id_v >= this->vscroll.GetCapacity()) break;
-
-				id_v += this->vscroll.GetPosition();
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, NLWW_MATRIX);
 				this->company = (id_v >= this->server->info.companies_on) ? INVALID_COMPANY : NetworkLobbyFindCompanyIndex(id_v);
 				this->SetDirty();
 
diff --git a/src/newgrf_debug_gui.cpp b/src/newgrf_debug_gui.cpp
index 019bd20b9..2fcef1c72 100644
--- a/src/newgrf_debug_gui.cpp
+++ b/src/newgrf_debug_gui.cpp
@@ -423,9 +423,8 @@ struct NewGRFInspectWindow : Window {
 				if (nif->variables == NULL) return;
 
 				/* Get the line, make sure it's within the boundaries. */
-				int line = (pt.y - this->GetWidget<NWidgetBase>(NIW_MAINPANEL)->pos_y - TOP_OFFSET) / this->resize.step_height;
-				if (line >= this->vscroll.GetCapacity()) return;
-				line += this->vscroll.GetPosition();
+				int line = this->vscroll.GetScrolledRowFromWidget(pt.y, this, NIW_MAINPANEL, TOP_OFFSET);
+				if (line == INT_MAX) return;
 
 				/* Find the variable related to the line */
 				for (const NIVariable *niv = nif->variables; niv->name != NULL; niv++, line--) {
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index 4570cab67..2d382c96f 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -482,8 +482,7 @@ struct NewGRFWindow : public QueryStringBaseWindow {
 			}
 
 			case SNGRFS_FILE_LIST: { // Select an active GRF.
-				NWidgetBase *nw = this->GetWidget<NWidgetBase>(SNGRFS_FILE_LIST);
-				uint i = (pt.y - nw->pos_y) / nw->resize_y + this->vscroll.GetPosition();
+				uint i = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SNGRFS_FILE_LIST);
 
 				GRFConfig *c;
 				for (c = this->actives; c != NULL && i > 0; c = c->next, i--) {}
@@ -526,8 +525,7 @@ struct NewGRFWindow : public QueryStringBaseWindow {
 			}
 
 			case SNGRFS_AVAIL_LIST: { // Select a non-active GRF.
-				NWidgetBase *nw = this->GetWidget<NWidgetBase>(SNGRFS_AVAIL_LIST);
-				uint i = (pt.y - nw->pos_y) / nw->resize_y + this->vscroll2.GetPosition();
+				uint i = this->vscroll2.GetScrolledRowFromWidget(pt.y, this, SNGRFS_AVAIL_LIST);
 				this->active_sel = NULL;
 				if (i < this->avails.Length()) {
 					this->avail_sel = this->avails[i];
diff --git a/src/news_gui.cpp b/src/news_gui.cpp
index 7e899fe84..c268604f1 100644
--- a/src/news_gui.cpp
+++ b/src/news_gui.cpp
@@ -1014,7 +1014,7 @@ struct MessageHistoryWindow : Window {
 			NewsItem *ni = _latest_news;
 			if (ni == NULL) return;
 
-			for (int n = (pt.y - this->GetWidget<NWidgetBase>(MHW_BACKGROUND)->pos_y - WD_FRAMERECT_TOP) / this->line_height + this->vscroll.GetPosition(); n > 0; n--) {
+			for (int n = this->vscroll.GetScrolledRowFromWidget(pt.y, this, MHW_BACKGROUND, WD_FRAMERECT_TOP, this->line_height); n > 0; n--) {
 				ni = ni->prev;
 				if (ni == NULL) return;
 			}
diff --git a/src/rail_gui.cpp b/src/rail_gui.cpp
index 4a3101491..34e7034a5 100644
--- a/src/rail_gui.cpp
+++ b/src/rail_gui.cpp
@@ -1327,10 +1327,7 @@ public:
 
 			case BRSW_NEWST_LIST: {
 				const StationSpec *statspec;
-				int y = (pt.y - this->GetWidget<NWidgetBase>(BRSW_NEWST_LIST)->pos_y) / this->line_height;
-
-				if (y >= this->vscroll.GetCapacity()) return;
-				y += this->vscroll.GetPosition();
+				int y = this->vscroll.GetScrolledRowFromWidget(pt.y, this, BRSW_NEWST_LIST, 0, this->line_height);
 				if (y >= _railstation.station_count) return;
 
 				/* Check station availability callback */
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index abb0bf389..3ec335146 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -1550,11 +1550,8 @@ struct GameSettingsWindow : Window {
 	{
 		if (widget != SETTINGSEL_OPTIONSPANEL) return;
 
-		int y = pt.y - this->GetWidget<NWidgetBase>(widget)->pos_y - SETTINGTREE_TOP_OFFSET;  // Shift y coordinate
-		if (y < 0) return;  // Clicked above first entry
-
-		byte btn = this->vscroll.GetPosition() + y / this->resize.step_height;  // Compute which setting is selected
-		if (y % this->resize.step_height > this->resize.step_height - 2) return;  // Clicked too low at the setting
+		uint btn = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SETTINGSEL_OPTIONSPANEL, SETTINGTREE_TOP_OFFSET - 1);
+		if (btn == INT_MAX) return;
 
 		uint cur_row = 0;
 		SettingEntry *pe = _settings_main_page.FindEntry(btn, &cur_row);
diff --git a/src/signs_gui.cpp b/src/signs_gui.cpp
index 237af085e..a054d0fed 100644
--- a/src/signs_gui.cpp
+++ b/src/signs_gui.cpp
@@ -148,11 +148,8 @@ struct SignListWindow : Window, SignList {
 	virtual void OnClick(Point pt, int widget, int click_count)
 	{
 		if (widget == SLW_LIST) {
-			uint id_v = (pt.y - this->GetWidget<NWidgetBase>(SLW_LIST)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height;
-
-			if (id_v >= this->vscroll.GetCapacity()) return;
-			id_v += this->vscroll.GetPosition();
-			if (id_v >= this->vscroll.GetCount()) return;
+			uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SLW_LIST, WD_FRAMERECT_TOP);
+			if (id_v == INT_MAX) return;
 
 			const Sign *si = this->signs[id_v];
 			ScrollMainWindowToTile(TileVirtXY(si->x, si->y));
diff --git a/src/station_gui.cpp b/src/station_gui.cpp
index 4fe500f64..30034cc16 100644
--- a/src/station_gui.cpp
+++ b/src/station_gui.cpp
@@ -535,12 +535,7 @@ public:
 	{
 		switch (widget) {
 			case SLW_LIST: {
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(SLW_LIST)->pos_y - WD_FRAMERECT_TOP) / FONT_HEIGHT_NORMAL;
-
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SLW_LIST, 0, FONT_HEIGHT_NORMAL);
 				if (id_v >= this->stations.Length()) return; // click out of list bound
 
 				const Station *st = this->stations[id_v];
@@ -1152,7 +1147,7 @@ struct StationViewWindow : public Window {
 	{
 		switch (widget) {
 			case SVW_WAITING:
-				this->HandleCargoWaitingClick((pt.y - this->GetWidget<NWidgetBase>(SVW_WAITING)->pos_y - WD_FRAMERECT_TOP) / FONT_HEIGHT_NORMAL + this->vscroll.GetPosition());
+				this->HandleCargoWaitingClick(this->vscroll.GetScrolledRowFromWidget(pt.y, this, SVW_WAITING, WD_FRAMERECT_TOP, FONT_HEIGHT_NORMAL));
 				break;
 
 			case SVW_LOCATION:
@@ -1416,7 +1411,7 @@ struct SelectStationWindow : Window {
 	{
 		if (widget != JSW_PANEL) return;
 
-		uint32 st_index = (pt.y - this->GetWidget<NWidgetBase>(JSW_PANEL)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height + this->vscroll.GetPosition();
+		uint st_index = this->vscroll.GetScrolledRowFromWidget(pt.y, this, JSW_PANEL, WD_FRAMERECT_TOP);
 		bool distant_join = (st_index > 0);
 		if (distant_join) st_index--;
 
diff --git a/src/subsidy_gui.cpp b/src/subsidy_gui.cpp
index 0528ea146..09c43bd84 100644
--- a/src/subsidy_gui.cpp
+++ b/src/subsidy_gui.cpp
@@ -41,11 +41,7 @@ struct SubsidyListWindow : Window {
 	{
 		if (widget != SLW_PANEL) return;
 
-		int y = (pt.y - this->GetWidget<NWidgetBase>(SLW_PANEL)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height;
-		if (!IsInsideMM(y, 0, this->vscroll.GetCapacity())) return;
-
-		y += this->vscroll.GetPosition();
-
+		int y = this->vscroll.GetScrolledRowFromWidget(pt.y, this, SLW_PANEL, WD_FRAMERECT_TOP);
 		int num = 0;
 		const Subsidy *s;
 		FOR_ALL_SUBSIDIES(s) {
diff --git a/src/town_gui.cpp b/src/town_gui.cpp
index dc6864f20..4d5cddb1c 100644
--- a/src/town_gui.cpp
+++ b/src/town_gui.cpp
@@ -873,12 +873,7 @@ public:
 				break;
 
 			case TDW_CENTERTOWN: { // Click on Town Matrix
-				uint16 id_v = (pt.y - this->GetWidget<NWidgetBase>(widget)->pos_y - WD_FRAMERECT_TOP) / this->resize.step_height;
-
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, TDW_CENTERTOWN, WD_FRAMERECT_TOP);
 				if (id_v >= this->towns.Length()) return; // click out of town bounds
 
 				const Town *t = this->towns[id_v];
diff --git a/src/vehicle_gui.cpp b/src/vehicle_gui.cpp
index 3650bd9a3..527068da1 100644
--- a/src/vehicle_gui.cpp
+++ b/src/vehicle_gui.cpp
@@ -528,11 +528,8 @@ struct RefitWindow : public Window {
 	{
 		switch (widget) {
 			case VRW_MATRIX: { // listbox
-				int y = pt.y - this->GetWidget<NWidgetBase>(VRW_MATRIX)->pos_y;
-				if (y >= 0) {
-					this->sel = (y / (int)this->resize.step_height) + this->vscroll.GetPosition();
-					this->InvalidateData(1);
-				}
+				this->sel = this->vscroll.GetScrolledRowFromWidget(pt.y, this, VRW_MATRIX);
+				this->InvalidateData(1);
 
 				if (click_count == 1) break;
 			}
@@ -1213,13 +1210,8 @@ public:
 				return;
 
 			case VLW_WIDGET_LIST: { // Matrix to show vehicles
-				uint32 id_v = (pt.y - this->GetWidget<NWidgetBase>(VLW_WIDGET_LIST)->pos_y) / this->resize.step_height;
 				const Vehicle *v;
-
-				if (id_v >= this->vscroll.GetCapacity()) return; // click out of bounds
-
-				id_v += this->vscroll.GetPosition();
-
+				uint id_v = this->vscroll.GetScrolledRowFromWidget(pt.y, this, VLW_WIDGET_LIST);
 				if (id_v >= this->vehicles.Length()) return; // click out of list bound
 
 				v = this->vehicles[id_v];