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

        private void BitmapSelector_MouseMove(object sender, MouseEventArgs e)
        {
            //so we can capture the mouse wheel event
            if (!Focused)
                this.Focus();

            Point p = Translate(e.Location);

            if (p == mouseLast)
                return;
            if (p.X < 0 || p.X >= Width || p.Y < 0 || p.Y >= Height)
                return;
            if (!mouse1Down && !mouse2Down && ShowToolTips && ToolTips[p.X, p.Y] != null && ToolTips[p.X, p.Y].Length > 0)
                toolTip.Show(ToolTips[p.X, p.Y], this, new Point(e.X + 1, e.Y + 1));
            else
                toolTip.Hide(this);

            bool needToRedraw = false;
            if ((mouse1Down || mouse2Down) && (Brush == BrushType.Round || Brush == BrushType.Square))
            {
                using (Graphics g = Graphics.FromImage(Layers[SelectionLayerIndex].Image))
                {
                    if (!SelectionBounds.IsEmpty)
                        g.SetClip(SelectionBounds);
                    g.CompositingMode = CompositingMode.SourceCopy;
                    Pen pen = new Pen(mouse1Down ? SelectionColor : Color.Transparent, BrushDiameter);
                    SolidBrush b = new SolidBrush(mouse1Down ? SelectionColor : Color.Transparent);

                    if (Brush == BrushType.Round)
                    {
                        g.DrawLine(pen, mouseLast, p);
                        g.FillEllipse(b, p.X - BrushDiameter / 2, p.Y - BrushDiameter / 2, BrushDiameter, BrushDiameter);
                    }
                    else //Square
                    {
                        if (BrushDiameter == 1)
                        {
                            g.DrawLine(pen, mouseLast, p);
                        }
                        else
                        {
                            Point[] parallelogram = new Point[4];
                            double m = ((double)(p.Y - mouseLast.Y)) / ((double)(p.X - mouseLast.X));
                            if (m < 0.0)
                            {
                                parallelogram[0] = new Point(p.X - (int)(BrushDiameter / 2.0), p.Y - (int)(BrushDiameter / 2.0));
                                parallelogram[1] = new Point(p.X + (int)(BrushDiameter / 2.0), p.Y + (int)(BrushDiameter / 2.0));
                                parallelogram[2] = new Point(mouseLast.X + (int)(BrushDiameter / 2.0), mouseLast.Y + (int)(BrushDiameter / 2.0));
                                parallelogram[3] = new Point(mouseLast.X - (int)(BrushDiameter / 2.0), mouseLast.Y - (int)(BrushDiameter / 2.0));
                            }
                            else
                            {
                                parallelogram[0] = new Point(p.X + (int)(BrushDiameter / 2.0), p.Y - (int)(BrushDiameter / 2.0));
                                parallelogram[1] = new Point(p.X - (int)(BrushDiameter / 2.0), p.Y + (int)(BrushDiameter / 2.0));
                                parallelogram[2] = new Point(mouseLast.X - (int)(BrushDiameter / 2.0), mouseLast.Y + (int)(BrushDiameter / 2.0));
                                parallelogram[3] = new Point(mouseLast.X + (int)(BrushDiameter / 2.0), mouseLast.Y - (int)(BrushDiameter / 2.0));
                            }
                            g.FillPolygon(b, parallelogram);
                        }

                        g.FillRectangle(b, p.X - BrushDiameter / 2, p.Y - BrushDiameter / 2, BrushDiameter, BrushDiameter);

                    }

                    pen.Dispose();
                    b.Dispose();
                }

                needToRedraw = true;
            }

            if (Layers[BrushLayerIndex].Visible)
            {
                RedrawBrushLayer(p);
                needToRedraw = true;
            }

            if (needToRedraw)
                Redraw();

            mouseLast = p;
        }