src/Screen/Ramp.cpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2012 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #include "Screen/Ramp.hpp"
  25
  26 #include <assert.h>
  27 #include <stddef.h>
  28
  29 Color
  30 ColorRampLookup(const short h,
  31                 const ColorRamp* ramp_colors,
  32                 const int numramp,
  33                 const unsigned char interp_levels)
  34 {
  35   assert(ramp_colors != NULL);
  36   assert(numramp >= 2);
  37
  38   unsigned short f, of;
  39   unsigned short is = 1<<interp_levels;
  40
  41   // gone past end, so use last color
  42   if (h >= ramp_colors[numramp - 1].h) {
  43     return Color(ramp_colors[numramp-1].r,
  44                  ramp_colors[numramp-1].g,
  45                  ramp_colors[numramp-1].b);
  46   }
  47   for (int i = numramp - 2; i >= 0; i--) {
  48     assert(ramp_colors[i].h < ramp_colors[i + 1].h);
  49
  50     if (h >= ramp_colors[i].h) {
  51       if (interp_levels) {
  52         f = (unsigned short)(h - ramp_colors[i].h) * is
  53           / (unsigned short)(ramp_colors[i + 1].h - ramp_colors[i].h);
  54         of = is - f;
  55
  56         return Color((f * ramp_colors[i + 1].r + of * ramp_colors[i].r) >> interp_levels,
  57                      (f * ramp_colors[i + 1].g + of * ramp_colors[i].g) >> interp_levels,
  58                      (f * ramp_colors[i + 1].b + of * ramp_colors[i].b) >> interp_levels);
  59       } else {
  60         return Color(ramp_colors[i].r, ramp_colors[i].g, ramp_colors[i].b);
  61       }
  62     }
  63   }
  64
  65   // check if h lower than lowest
  66   assert(h <= ramp_colors[0].h);
  67
  68   return Color(ramp_colors[0].r, ramp_colors[0].g, ramp_colors[0].b);
  69 }