Improve and extend fl_contrast() (#370)

- Add internal fl_contrast_cielab() as the new default.
- Keep old function as internal fl_contrast_legacy().
- Add fl_contrast_mode() to switch between fl_contrast() functions.
- Add fl_contrast_level() to fine tune fl_contrast() per mode.
- Add option to register and use a custom contrast function.
- Add test/contrast.cxx test program.
- Move all fl_contrast() related code to a new file src/fl_contrast.cxx.
- Add fl_lightness() convenience function for perceived lightness.
- Add fl_luminance() convenience function for physical luminance.

1 files changed, 0 insertions, 30 deletions

diff --git a/src/fl_color.cxx b/src/fl_color.cxx
index d925a73ee..dd1f07066 100644
--- a/src/fl_color.cxx
+++ b/src/fl_color.cxx
@@ -169,35 +169,5 @@ Fl_Color fl_inactive(Fl_Color c) {
 }
 
 /**
- Returns a color that contrasts with the background color.
-
- This will be the foreground color if it contrasts sufficiently with the
- background color. Otherwise, returns \p FL_WHITE or \p FL_BLACK depending
- on which color provides the best contrast.
- \param[in] fg,bg foreground and background colors
- \return contrasting color
- */
-Fl_Color fl_contrast(Fl_Color fg, Fl_Color bg) {
-  unsigned c1, c2;      // RGB colors
-  int l1, l2;           // Luminosities
-
-  // Get the RGB values for each color...
-  if (fg & 0xffffff00) c1 = (unsigned)fg;
-  else c1 = fl_cmap[fg];
-
-  if (bg & 0xffffff00) c2 = (unsigned)bg;
-  else c2 = fl_cmap[bg];
-
-  // Compute the luminosity...
-  l1 = ((c1 >> 24) * 30 + ((c1 >> 16) & 255) * 59 + ((c1 >> 8) & 255) * 11) / 100;
-  l2 = ((c2 >> 24) * 30 + ((c2 >> 16) & 255) * 59 + ((c2 >> 8) & 255) * 11) / 100;
-
-  // Compare and return the contrasting color...
-  if ((l1 - l2) > 99) return fg;
-  else if ((l2 - l1) > 99) return fg;
-  else if (l2 > 127) return FL_BLACK;
-  else return FL_WHITE;
-}
-/**
  \}
  */