反轉文本顏色取決於背景色

Question

我有一個ProgressBar控制，如以下兩個：

首先是正確畫。正如你所看到的，第二個只有一個0，它應該有兩個，但另一個不能被看到，因爲ProgressBar的ForeColor與TextColor相同。有什麼方法可以將下面的ProgressBar畫在石灰上，並在背景是黑色時將石灰畫在石灰上，這樣我可以將文本塗成黑色？

Answer 1

你可以先繪製背景和文本，然後繪製使用PatBlt方法的前景石灰矩形PATINVERT參數前景繪製背景繪畫相結合：

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：這些控件僅用於演示繪畫邏輯。對於真實世界的應用程序，您需要在Minimum，Maximum和Value屬性上添加一些驗證。