HeapProfiler.DeltaList.OnPaint C# (CSharp) Method

        protected override void OnPaint(PaintEventArgs e)
        {
            bool retrying = false, selectedItemVisible = false;
            int minVisibleIndex = int.MaxValue,  maxVisibleIndex = int.MinValue;
            var width = ClientSize.Width - ScrollBar.Width;

            retryFromHere:

            if (_SelectedIndex >= Items.Count)
                _SelectedIndex = Items.Count - 1;
            if (_SelectedIndex < 0)
                _SelectedIndex = 0;

            if (_ScrollOffset >= Items.Count)
                _ScrollOffset = Items.Count - 1;
            if (_ScrollOffset < 0)
                _ScrollOffset = 0;

            VisibleItems.Clear();

            ItemData data;

            using (var sf = new StringFormat {
                Alignment = StringAlignment.Near,
                LineAlignment = StringAlignment.Near,
                FormatFlags = StringFormatFlags.FitBlackBox | StringFormatFlags.NoWrap |
                    StringFormatFlags.DisplayFormatControl | StringFormatFlags.MeasureTrailingSpaces,
                HotkeyPrefix = System.Drawing.Text.HotkeyPrefix.None,
                Trimming = StringTrimming.None
            })
            using (var shadeBrush = new SolidBrush(Color.FromArgb(31, 0, 0, 0)))
            using (var elideBackgroundBrush = new SolidBrush(Color.FromArgb(192, SystemColors.Window)))
            using (var elideTextBrush = new SolidBrush(Color.FromArgb(220, SystemColors.WindowText)))
            using (var backgroundBrush = new SolidBrush(BackColor))
            using (var textBrush = new SolidBrush(ForeColor))
            using (var highlightBrush = new SolidBrush(SystemColors.Highlight))
            using (var highlightTextBrush = new SolidBrush(SystemColors.HighlightText)) {
                var lineHeight = e.Graphics.MeasureString("AaBbYyZz", Font, width, sf).Height;
                CollapsedSize = (int)Math.Ceiling(lineHeight * 3);

                var renderParams = new DeltaInfo.RenderParams {
                    Font = Font,
                    FunctionFilter = FunctionFilter,
                    FunctionHighlightBrush = highlightBrush,
                    FunctionHighlightTextBrush = highlightTextBrush,
                    ElideBackgroundBrush = elideBackgroundBrush,
                    ElideTextBrush = elideTextBrush,
                    ShadeBrush = shadeBrush,
                    StringFormat = sf,
                };

                int y = 0;
                for (int i = _ScrollOffset; (i < Items.Count) && (y < ClientSize.Height); i++) {
                    var y1 = y;
                    var selected = (i == SelectedIndex);

                    var item = Items[i];
                    GetItemData(i, out data);

                    var rgn = new Rectangle(
                        0, y, width,
                        data.Expanded ?
                            (int)Math.Ceiling(lineHeight * (item.Traceback.Frames.Count + 1)) :
                            CollapsedSize
                    );

                    using (var scratch = Scratch.Get(e.Graphics, rgn)) {
                        var g = scratch.Graphics;

                        g.ResetClip();
                        g.Clear(selected ? highlightBrush.Color : backgroundBrush.Color);

                        renderParams.BackgroundColor = selected ? highlightBrush.Color : backgroundBrush.Color;
                        renderParams.BackgroundBrush = selected ? highlightBrush : backgroundBrush;
                        renderParams.TextBrush = selected ? highlightTextBrush : textBrush;

                        renderParams.ContentRegion = rgn;
                        renderParams.IsExpanded = data.Expanded;
                        renderParams.IsSelected = selected;

                        y += (int)Math.Ceiling(item.Render(g, ref renderParams));
                    }

                    VisibleItems.Add(new VisibleItem {
                        Y1 = y1, Y2 = y, Index = i
                    });

                    if ((y1 >= 0) && (y < ClientSize.Height) || ((y - y1) >= ClientSize.Height)) {
                        minVisibleIndex = Math.Min(minVisibleIndex, i);
                        maxVisibleIndex = Math.Max(maxVisibleIndex, i);
                        selectedItemVisible |= selected;
                    }
                }

                if (y < ClientSize.Height)
                    e.Graphics.FillRectangle(backgroundBrush, new Rectangle(0, y, ClientSize.Width, ClientSize.Height - y));
            }

            if (!selectedItemVisible && !retrying && ShouldAutoscroll) {
                if (_SelectedIndex > maxVisibleIndex)
                    _ScrollOffset += _SelectedIndex - maxVisibleIndex;
                else if (_SelectedIndex < minVisibleIndex)
                    _ScrollOffset -= minVisibleIndex - _SelectedIndex;

                if (_ScrollOffset >= Items.Count)
                    _ScrollOffset = Items.Count - 1;
                if (_ScrollOffset < 0)
                    _ScrollOffset = 0;

                retrying = true;
                goto retryFromHere;
            }

            int largeChange = Math.Max(4, ClientSize.Height / CollapsedSize);
            if (ScrollBar.LargeChange != largeChange)
                ScrollBar.LargeChange = largeChange;

            int scrollMax = Math.Max(1, Items.Count - 1) + largeChange - 1;
            if (ScrollBar.Maximum != scrollMax)
                ScrollBar.Maximum = scrollMax;
            if (ScrollBar.Value != ScrollOffset)
                ScrollBar.Value = ScrollOffset;

            ShouldAutoscroll = false;
            base.OnPaint(e);
        }