# HG changeset patch
# Parent 362268611cc9e381cbeb313dc4c2fdf1f46491d4
# User sbr
# Date 1348905329 -7200

Feature(ette): Ensure proper contrast between colour and abbreviation for cargo buttons in CompanyStationsWindow.
Calculate brightness of rating_colour to determine the text colour to use for writing the cargo abbrev
(see http://www.nbdtech.com/Blog/archive/2008/04/27/Calculating-the-Perceived-Brightness-of-a-Color.aspx,
http://alienryderflex.com/hsp.html and http://www.w3.org/TR/AERT#color-contrast).

diff -r 362268611cc9 src/station_gui.cpp
--- a/src/station_gui.cpp	Tue Nov 06 18:45:08 2012 +0000
+++ b/src/station_gui.cpp	Wed Nov 07 18:09:22 2012 +0100
@@ -30,6 +30,7 @@
 #include "core/geometry_func.hpp"
 #include "vehiclelist.h"
 #include "town.h"
+#include <math.h>
 
 #include "widgets/station_widget.h"
 
@@ -454,8 +455,13 @@
 				if (widget >= WID_STL_CARGOSTART) {
 					const CargoSpec *cs = _sorted_cargo_specs[widget - WID_STL_CARGOSTART];
 					int cg_ofst = HasBit(this->cargo_filter, cs->Index()) ? 2 : 1;
+					/* Ensure proper contrast between cargo abbrev and rating colour. */
+					Colour rc = _cur_palette.palette[cs->rating_colour];
+					uint brightness = (uint) sqrt(rc.r * rc.r * 0.299 + rc.g * rc.g * 0.587 + rc.b * rc.b * 0.114);
+					TextColour tc = brightness < 70 ? TC_WHITE : TC_BLACK;
+
 					GfxFillRect(r.left + cg_ofst, r.top + cg_ofst, r.right - 2 + cg_ofst, r.bottom - 2 + cg_ofst, cs->rating_colour);
-					DrawString(r.left + cg_ofst, r.right + cg_ofst, r.top + cg_ofst, cs->abbrev, TC_BLACK, SA_HOR_CENTER);
+					DrawString(r.left + cg_ofst, r.right + cg_ofst, r.top + cg_ofst, cs->abbrev, tc, SA_HOR_CENTER);
 				}
 				break;
 		}