反转文本颜色取决于背景色

Question

我有一个ProgressBar控制，如以下两个：

首先是正确画。正如你所看到的，第二个只有一个0，它应该有两个，但另一个不能被看到，因为ProgressBar的ForeColor与TextColor相同。有什么方法可以将下面的ProgressBar画在石灰上，并在背景是黑色时将石灰画在石灰上，这样我可以将文本涂成黑色？

Answer 1

你可以先绘制背景和文本，然后绘制使用PatBlt方法的前景石灰矩形PATINVERT参数前景绘制背景绘画相结合：

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(((c.R | (c.G << 8)) | (c.B << 16))); 
     var phbrush = SelectObject(hdc, hbrush); 
     PatBlt(hdc, r.Left, r.Y, (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); 
} 

注意：这些控件仅用于演示绘画逻辑。对于真实世界的应用程序，您需要在Minimum，Maximum和Value属性上添加一些验证。