From 40faaa46f4ab3a34affb211ced6e2db076b71cd0 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Thu, 20 Jul 2023 10:43:10 +0100
Subject: [PATCH] Scroll to class when using picker tool on object

See: #572
---
 src/object_gui.cpp | 36 ++++++++++++++++++++++++++++++++++++
 src/window.cpp     | 16 ++++++++++++++++
 src/window_gui.h   |  1 +
 3 files changed, 53 insertions(+)

diff --git a/src/object_gui.cpp b/src/object_gui.cpp
index a7d4d9baf93..30527b4e5ab 100644
--- a/src/object_gui.cpp
+++ b/src/object_gui.cpp
@@ -417,6 +417,24 @@ class BuildObjectWindow : public Window {
 		}
 	}
 
+	/**
+	 * Clear class filter if the selected class is not included in the filter.
+	 * @param object_class Object class select.
+	 */
+	void ClearFilterIsClassNotIncluded(ObjectClassID object_class)
+	{
+		/* Filter is not enabled */
+		if (!this->object_classes.IsFilterEnabled()) return;
+
+		for (auto oc : this->object_classes) {
+			if (oc == object_class) {
+				return;
+			}
+		}
+
+		this->ClearEditBox(WID_BO_FILTER);
+	}
+
 	/**
 	 * Select the specified object class.
 	 * @param object_class Object class select.
@@ -456,6 +474,22 @@ class BuildObjectWindow : public Window {
 		this->UpdateButtons(_selected_object_class, _selected_object_index, _selected_object_view);
 	}
 
+	/**
+	 * Scrolls #WID_BO_SCROLLBAR so that the selected class is visible.
+	 */
+	void EnsureSelectedClassIsVisible()
+	{
+		uint pos = 0;
+		for (auto object_class : this->object_classes) {
+			if (object_class == _selected_object_class) {
+				this->vscroll->SetCount(this->object_classes.size());
+				this->vscroll->ScrollTowards(pos);
+				return;
+			}
+			pos++;
+		}
+	}
+
 	void UpdateSelectSize()
 	{
 		if (_selected_object_index == -1) {
@@ -760,8 +794,10 @@ void ShowBuildObjectPickerAndSelect(const ObjectSpec *spec)
 
 	BuildObjectWindow *w = AllocateWindowDescFront<BuildObjectWindow>(&_build_object_desc, 0, true);
 	if (w != nullptr) {
+		w->ClearFilterIsClassNotIncluded(spec->cls_id);
 		w->SelectOtherClass(spec->cls_id);
 		w->SelectOtherObject(spec_id);
+		w->EnsureSelectedClassIsVisible();
 	}
 }
 
diff --git a/src/window.cpp b/src/window.cpp
index fd09fdd1e49..fbeca40516e 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -2755,6 +2755,22 @@ EventState Window::HandleEditBoxKey(int wid, WChar key, uint16 keycode)
 	return ES_HANDLED;
 }
 
+/**
+ * Clear editbox widget.
+ * @param wid Editbox widget.
+ * @return if the Editbox was successfully cleared
+ */
+bool Window::ClearEditBox(int wid)
+{
+	QueryString *query = this->GetQueryString(wid);
+	if (query == nullptr) return false;
+
+	query->text.DeleteAll();
+	this->SetWidgetDirty(wid);
+	this->OnEditboxChanged(wid);
+	return true;
+}
+
 /**
  * Focus a window by its class and window number (if it is open).
  * @param cls Window class.
diff --git a/src/window_gui.h b/src/window_gui.h
index eadd59e17fd..a16c99f2210 100644
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -506,6 +506,7 @@ struct Window : WindowBase {
 	bool SetFocusedWidget(int widget_index);
 
 	EventState HandleEditBoxKey(int wid, WChar key, uint16 keycode);
+	bool ClearEditBox(int wid);
 	virtual void InsertTextString(int wid, const char *str, bool marked, const char *caret, const char *insert_location, const char *replacement_end);
 
 	void HandleButtonClick(byte widget);