Invert text color depending on BackColor

Question

I have a ProgressBar control as shown below:

The first is correctly colored. As you can see, the second one has only one 0, it must have two, and the other cannot be seen, because ProgressBar ForeColor same as TextColor . Is there a way to draw text in black when the ProgressBar below is drawn in Lime and draw text in Lime when the background is black?

Answer 1

You can first draw a background and text, and then draw a rectangle lime in the foreground using the PatBlt method with the PATINVERT parameter to combine the foreground picture with the background painting:

 using System; using System.Drawing; using System.Runtime.InteropServices; using System.Windows.Forms; 

 public class MyProgressBar : Control { public MyProgressBar() { DoubleBuffered = true; Minimum = 0; Maximum = 100; Value = 50; } public int Minimum { get; set; } public int Maximum { get; set; } public int Value { get; set; } protected override void OnPaint(PaintEventArgs e) { base.OnPaint(e); Draw(e.Graphics); } private void Draw(Graphics g) { var r = this.ClientRectangle; using (var b = new SolidBrush(this.BackColor)) g.FillRectangle(b, r); TextRenderer.DrawText(g, this.Value.ToString(), this.Font, r, this.ForeColor); var hdc = g.GetHdc(); var c = this.ForeColor; var hbrush = CreateSolidBrush(((cR | (cG << 8)) | (cB << 16))); var phbrush = SelectObject(hdc, hbrush); PatBlt(hdc, r.Left, rY, (Value * r.Width / Maximum), r.Height, PATINVERT); SelectObject(hdc, phbrush); DeleteObject(hbrush); g.ReleaseHdc(hdc); } public const int PATINVERT = 0x005A0049; [DllImport("gdi32.dll")] public static extern bool PatBlt(IntPtr hdc, int nXLeft, int nYLeft, int nWidth, int nHeight, int dwRop); [DllImport("gdi32.dll")] public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj); [DllImport("gdi32.dll", EntryPoint = "DeleteObject")] public static extern bool DeleteObject(IntPtr hObject); [DllImport("gdi32.dll")] public static extern IntPtr CreateSolidBrush(int crColor); } 

Note: The controls are intended only to demonstrate drawing logic. For real applications, you need to add some checks on the Minimum , Maximum and Value properties.