BiomePainter.BitmapSelector.BitmapSelector.RedrawBrushLayer C# (CSharp) Method

        private void RedrawBrushLayer(Point p, bool justClear = false)
        {
            using (Graphics g = Graphics.FromImage(Layers[BrushLayerIndex].Image))
            {
                g.Clear(Color.Transparent);
                if (!SelectionBounds.IsEmpty)
                    g.SetClip(SelectionBounds);

                if (!justClear)
                {
                    if (customBrush != null)
                    {
                        g.DrawImage(customBrush, p.X - (customBrush.Width >> 1), p.Y - (customBrush.Height >> 1));
                    }
                    else
                    {
                        if (SelectionBounds.IsEmpty || SelectionBounds.Contains(p))
                            Layers[BrushLayerIndex].Image.SetPixel(p.X, p.Y, Color.Black);
                        Brush b = new SolidBrush(Color.Black);
                        if (Brush == BrushType.Rectangle)
                        {
                            if ((mouse1Down || mouse2Down) && mouseDownLast.X != -1 && mouseDownLast.Y != -1)
                            {
                                g.FillRectangle(b, Rectangle.FromLTRB(Math.Min(mouseDownLast.X, p.X), Math.Min(mouseDownLast.Y, p.Y), Math.Max(mouseDownLast.X, p.X), Math.Max(mouseDownLast.Y, p.Y)));
                            }
                        }
                        else if (Brush == BrushType.Round)
                        {
                            g.FillEllipse(b, p.X - BrushDiameter / 2, p.Y - BrushDiameter / 2, BrushDiameter, BrushDiameter);
                        }
                        else if (Brush == BrushType.Square)
                        {
                            g.FillRectangle(b, p.X - BrushDiameter / 2, p.Y - BrushDiameter / 2, BrushDiameter, BrushDiameter);
                        }
                        b.Dispose();
                    }
                }
            }
        }