Get a correct text color from a back color !

Did you try to XOR your text color with the back color ?

If I do this, the text color becomes the same as the back color.

COLORREF clrText = RGB(0,0,0); // default text color is black
COLORREF clrBack = RGB(0,0,0); // background color is black

=> text color must becomes white

clrText = clrText ^ clrBack => black ?

Even in a professional program if you draw white color line to a white background you wont notice it.

But if you want to see it black

clrText = !(clrText ^ clrBack)

It doens't works. The text color stays back on a dark background color.

But I have found a solution using the luminance value :

double GetLuminance(COLORREF clr)
 {
  return 0.3 * GetRValue(clr) + 0.59 * GetGValue(clr) + 0.11 * GetBValue(clr);
 }

COLORREF clrText = GetLuminance() < 120.0 ? RGB(255,255,255) : RGB(0,0,0);

Sounds to be a good one but I am not sure if 120 will always work.