Added VirtualFlowControl and BookQueue

Source/LibationWinForms/ProcessQueue/VirtualFlowControl.cs

@@ -0,0 +1,146 @@
+using System;
+using System.Drawing;
+using System.Windows.Forms;
+
+namespace LibationWinForms.ProcessQueue
+{
+
+	internal delegate void RequestDataDelegate(int firstIndex, int numVisible, ProcessBookControl[] panelsToFill);
+	internal partial class VirtualFlowControl : UserControl
+	{
+		public event RequestDataDelegate RequestData;
+		public int VirtualControlCount
+		{
+			get => _virtualControlCount;
+			set
+			{
+				if (_virtualControlCount == 0) 
+					vScrollBar1.Value = 0;
+
+				_virtualControlCount = value;
+				AdjustScrollBar();
+				DoVirtualScroll();
+			}
+		}
+
+		private int _virtualControlCount;
+		private int VirtualHeight => _virtualControlCount * CONTROL_HEIGHT - vScrollBar1.Height;
+
+		private readonly int PROCESSBOOKCONTROL_MARGIN;
+		private readonly int CONTROL_HEIGHT;
+
+		private const int WM_MOUSEWHEEL = 522;
+		private const int NUM_ACTUAL_CONTROLS = 20;
+		private const int SCROLL_SMALL_CHANGE = 120;
+		private const int SCROLL_LARGE_CHANGE = 3 * SCROLL_SMALL_CHANGE;
+
+
+		private readonly VScrollBar vScrollBar1;
+		private readonly ProcessBookControl[] BookControls = new ProcessBookControl[NUM_ACTUAL_CONTROLS];
+
+		public VirtualFlowControl()
+		{
+
+			InitializeComponent();
+
+			vScrollBar1 = new VScrollBar
+			{
+				Minimum = 0,
+				Value = 0,
+				SmallChange = SCROLL_SMALL_CHANGE,
+				LargeChange = SCROLL_LARGE_CHANGE,
+				Dock = DockStyle.Right
+			};
+
+			Controls.Add(vScrollBar1);
+
+			panel1.Resize += (_, _) => AdjustScrollBar();
+
+			if (this.DesignMode)
+				return;
+
+			vScrollBar1.Scroll += (_, _) => DoVirtualScroll();
+
+			for (int i = 0; i < NUM_ACTUAL_CONTROLS; i++)
+			{
+				BookControls[i] = new ProcessBookControl();
+
+				if (i == 0)
+				{
+					PROCESSBOOKCONTROL_MARGIN = BookControls[i].Margin.Left + BookControls[i].Margin.Right;
+					CONTROL_HEIGHT = BookControls[i].Height + BookControls[i].Margin.Top + BookControls[i].Margin.Bottom;
+				}
+
+				BookControls[i].Location = new Point(2, CONTROL_HEIGHT * i);
+				BookControls[i].Width = panel1.ClientRectangle.Width - PROCESSBOOKCONTROL_MARGIN;
+				BookControls[i].Anchor = AnchorStyles.Left | AnchorStyles.Right | AnchorStyles.Top;
+				panel1.Controls.Add(BookControls[i]);
+			}
+
+			panel1.Height += SCROLL_SMALL_CHANGE;
+		}
+
+
+		private void AdjustScrollBar()
+		{
+			int maxFullVisible = DisplayRectangle.Height / CONTROL_HEIGHT;
+
+			if (VirtualControlCount <= maxFullVisible)
+			{
+				vScrollBar1.Enabled = false;
+
+				for (int i = VirtualControlCount; i < NUM_ACTUAL_CONTROLS; i++)
+					BookControls[i].Visible = false;
+			}
+			else
+			{
+				vScrollBar1.Enabled = true;
+				//https://stackoverflow.com/a/2882878/3335599
+				vScrollBar1.Maximum = VirtualHeight + vScrollBar1.LargeChange - 1;
+			}
+		}
+
+		private void DoVirtualScroll()
+		{
+			//https://stackoverflow.com/a/2882878/3335599
+			int scrollValue = Math.Max(Math.Min(VirtualHeight, vScrollBar1.Value), 0);
+
+			int position = scrollValue % CONTROL_HEIGHT;
+			panel1.Location = new Point(0, -position);
+
+			int firstVisible = scrollValue / CONTROL_HEIGHT;
+
+			int window = DisplayRectangle.Height;
+
+			int count = window / CONTROL_HEIGHT;
+
+			if (window % CONTROL_HEIGHT != 0)
+				count++;
+			count = Math.Min(count, VirtualControlCount);
+
+			RequestData?.Invoke(firstVisible, count, BookControls);
+
+			for (int i = 0; i < BookControls.Length; i++)
+				BookControls[i].Visible = i <= count && VirtualControlCount > 0;
+		}
+
+
+		protected override void WndProc(ref Message m)
+		{
+			if (m.Msg == WM_MOUSEWHEEL)
+			{
+				//https://docs.microsoft.com/en-us/windows/win32/inputdev/wm-mousewheel
+				int wheelDelta = -(short)(((ulong)m.WParam) >> 16 & 0xffff);
+
+				if (wheelDelta > 0)
+					vScrollBar1.Value = Math.Min(vScrollBar1.Value + wheelDelta, vScrollBar1.Maximum);
+				else
+					vScrollBar1.Value = Math.Max(vScrollBar1.Value + wheelDelta, vScrollBar1.Minimum);
+
+				DoVirtualScroll();
+			}
+
+			base.WndProc(ref m);
+		}
+	}
+}