1   
2   //If the user can change the background color of a component,
3   //make sure that the caption/text is displayed in a contrasting color.
4   
5   unit Unit1;
6   
7   interface
8   
9   uses
10    Windows, SysUtils, Graphics, Controls, Forms, StdCtrls, Buttons, ComCtrls,
11    Classes;
12  
13  type
14    TForm1 = class(TForm)
15      Edit1: TEdit;
16      BitBtn1: TBitBtn;
17      procedure BitBtn1Click(Sender: TObject);
18    end;
19  
20  var
21    Form1: TForm1;
22  
23  implementation
24  
25  {$R *.dfm}
26  
27  function ContrastColor(clBackground: TColor): TColor;
28  begin
29    with TRGBQuad(clBackground) do
30      if (rgbRed * 0.3) + (rgbGreen * 0.59) + (rgbBlue * 0.11) > 127.5 then
31        Result:= clBlack
32      else Result:= clWhite;
33  end;
34  
35  //To test:
36  procedure TForm1.BitBtn1Click(Sender: TObject);
37  begin
38    Edit1.Color:= Random(255) shl 16 + Random(255) shl 8 + Random(255);
39    Edit1.Font.Color:= ContrastColor(Edit1.Color);
40  end;
41  
42  end.