1   //If the user can change the background color of a component,
2   //make sure that the caption/text is displayed in a contrasting color.
3   //---------------------------------------------------------------------------
4   
5   #include <vcl.h>
6   #include <stdlib.h>
7   #pragma hdrstop
8   
9   #include "Unit1.h"
10  //---------------------------------------------------------------------------
11  #pragma package(smart_init)
12  #pragma resource "*.dfm"
13  TForm1 *Form1;
14  //---------------------------------------------------------------------------
15  __fastcall TForm1::TForm1(TComponent* Owner)
16          : TForm(Owner)
17  {
18  }
19  TColor ContrastColor(TColor clBackground){
20  
21     RGBQUAD *Quad1 = (RGBQUAD *)&clBackground;
22    if (((Quad1->rgbRed * 0.3) + (Quad1->rgbGreen * 0.59) + 
23         (Quad1->rgbBlue * 0.11)) > 127.5){
24        return clBlack;
25     }
26     else{
27     return  clWhite;
28    }
29  }
30  
31  //---------------------------------------------------------------------------
32  
33  void __fastcall TForm1::Button1Click(TObject *Sender)
34  {
35  Edit1->Color= random(255) << 16 + random(255) << 8 + random(255);
36   Edit1->Font->Color = ContrastColor(Edit1->Color);
37  
38  }
39  //---------------------------------------------------------------------------