#include <CtrlLib/CtrlLib.h>

using namespace Upp;
int count = 0;

struct ChildTest : Ctrl {
	int num=0;

	ChildTest() {
		SetFrame(BlackFrame());
		num = count;
		count++;
		SetRect(0, 0, 200, 50);
	}
	
	void Paint(Draw& w) override {
		LogPos lpos = GetPos();
		int y = lpos.y.GetA();
		auto sz = GetSize();
			
		w.DrawRect(sz, Color{ 255, 0, 0 } );
		
		String pos;
		pos << "item: " << num << " x: " << lpos.x.GetA() << " y: " << lpos.y.GetA();
		w.DrawText(10, 10, pos, Arial(14).Bold(), Color(0,0,0));
	}
};

struct App : TopWindow {
	ScrollBar          sb;
	int                count;
	Vector<ChildTest*> items;
	
	int GetLineHeight() {
		return 50;
	}

	virtual void Paint(Draw& w)
	{
		Size sz = GetSize();
		w.DrawRect(sz, SWhite);
		int fcy = GetLineHeight();
		int i = sb / fcy;
		int y = i * fcy - sb;
		
		String sbPos;
		sbPos << i;
		
		while(i < count && y < sz.cy) {
			auto item = items[i++];
			item->SetRect(0, y, 200, 45);
			y += fcy;
		}
		
		w.DrawText(200, 10, sbPos, Arial(14).Bold(), Color(0,0,0));
	}

	virtual void Layout()
	{
		sb.SetPage(GetSize().cy);
	}

	virtual void MouseWheel(Point, int zdelta, dword)
	{
		sb.Wheel(zdelta);
	}

	bool Key(dword key, int)
	{
		return sb.VertKey(key);
	}

	void SetCount(int n)
	{
		count = n;
		sb.SetTotal(n * GetLineHeight());
	}

	~App() {
		for(auto item : items) {
			delete item;
		}
	}

	App() {
		Sizeable().Zoomable().BackPaint();
		AddFrame(sb);
		sb.WhenScroll = [=] { Refresh(); };
		sb.SetLine(GetLineHeight());
		
		for(int i = 0; i < 100; i++) {
			ChildTest* ctrl = new ChildTest();
			ctrl->SetRect(0, i * 50, 200, 45);
			items.Add(ctrl);
			AddChild(ctrl);
		}
	}
};

GUI_APP_MAIN
{
	App app;
	app.SetRect(0, 0, 250, 500);
	app.SetCount(100);
	app.Run();
}

#include <CtrlLib/CtrlLib.h>

using namespace Upp;

struct ChildTest : Ctrl {
	int num=0;
	
	ChildTest(int num) : num(num) {
		SetFrame(BlackFrame());
		SetRect(0, 0, 200, 50);
	}
	
	void Paint(Draw& w) override {
		LogPos lpos = GetPos();
		int y = lpos.y.GetA();
		Size sz = GetSize();
			
		w.DrawRect(sz, AdjustIfDark(Color{ 255, 0, 0 }) );
		
		String pos;
		pos << "item: " << num << " x: " << lpos.x.GetA() << " y: " << lpos.y.GetA();
		w.DrawText(Zx(10), Zy(10), pos, Arial(14).Bold());
	}
};

struct App : TopWindow {
	ScrollBar          sb;
	Array<ChildTest>   items;
	
	int GetLineHeight() {
		return Zy(50);
	}

	void Sync() {
		for(int i = 0; i < items.GetCount(); i++)
			items[i].SetRect(0, i * GetLineHeight() - sb, Zx(200), Zy(45));
	}

	void Paint(Draw& w) override
	{
		Size sz = GetSize();
		w.DrawRect(sz, SWhite());
	}

	void Layout() override
	{
		sb.SetPage(GetSize().cy);
	}

	void MouseWheel(Point, int zdelta, dword) override
	{
		sb.Wheel(zdelta);
	}

	bool Key(dword key, int) override
	{
		return sb.VertKey(key);
	}

	App() {
		Sizeable().Zoomable(); // Backpaint is now default
		
		for(int i = 0; i < 100; i++)
			Add(items.Create<ChildTest>(i));
		
		AddFrame(sb);
		sb.WhenScroll = [=] { Sync(); };
		sb.SetLine(GetLineHeight());
		sb.SetTotal(items.GetCount() * GetLineHeight());

		Sync();
	}
};

GUI_APP_MAIN
{
	App app;
	app.SetRect(0, 0, Zx(250), Zy(500));
	app.Run();
}