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 // SPDX-FileCopyrightText: Lukas Sommer <sommerluk@gmail.com>
 // SPDX-License-Identifier: BSD-2-Clause OR MIT
 
 #ifndef CIELCHD50VALUES_H
 #define CIELCHD50VALUES_H
 
 #include "lchdouble.h"
 
 namespace PerceptualColor
 {
 /** @internal
  *
  * @brief CIELCH-D50 default values
  *
  * The @ref lchrangerationale "range of CIELCh-D50 values" it known.
  * But what could be useful default values? This struct provides some
  * proposals. All values are <tt>constexpr</tt>. */
 struct CielchD50Values final {
 public:
     /** @brief Maximum chroma value as defined in @ref lchrangerationale. */
     static constexpr int maximumChroma = 255;
     /** @brief Neutral chroma value
      *
      *  For chroma, a neutral value of 0 might be a good
      *  choice because it is less likely to make  out-of-gamut problems on
      *  any lightness (except maybe extreme white or extreme black). And
      *  it results in an achromatic color and is therefore perceived as
      *  neutral. */
     static constexpr int neutralChroma = 0;
     /** @brief Neutral hue value
      *
      *  For the hue, a default value of 0 might be used by convention. */
     static constexpr int neutralHue = 0;
     /** @brief Neutral lightness value
      *
      *  For the lightness, a neutral value of 50 seems a good choice as it
      *  is half the way in the defined lightness range of <tt>[0, 100]</tt>
      *  (thought not all gamuts offer the hole range of <tt>[0, 100]</tt>). As
      *  it is quite in the middle of the gamut solid, it allows for quite big
      *  values for chroma at different hues without falling out-of-gamut.
      *  Combined with a chroma of 0, it also approximates the color with
      *  the highest possible contrast against the hole surface of the
      *  gamut solid; this is interesting for background colors of
      *  gamut diagrams. */
     static constexpr int neutralLightness = 50;
     /** @brief Neutral gray color as Lab value.
      *
      * Neutral gray is a good choice for the background, as it is equally
      * distant from black and white, and also quite distant from any
      * saturated color.
      *
      * @todo Given that this might be used quite often, it could be useful
      * to provide the corresponding RGB value within @ref RgbColorSpace
      * as a property, returning a variable that is initialized on first
      * usage. */
     static constexpr LchDouble neutralGray{neutralLightness, //
                                            neutralChroma, //
                                            neutralHue};
     /** @brief Versatile chroma value in
      * <a href="http://www.littlecms.com/">LittleCMS</a>’ build-in
      * sRGB gamut
      *
      *  Depending on the use case, there might be an alternative to
      *  the neutral gray @ref neutralChroma. For a lightness of 50, this
      *  value is the maximum chroma available at all possible hues within
      *  a usual sRGB gamut.
      *
      *  @sa @ref neutralChroma
      *
      * @todo This value should be removed in favor of using individual
      * values for each gamut. */
     static constexpr int srgbVersatileChroma = 32;
     /** @brief Versatile initial color for widgets in
      * <a href="http://www.littlecms.com/">LittleCMS</a>’ build-in
      * sRGB gamut
      *
      * This provides a colorful (non-gray) initial color.
      *
      * The lightness and the chroma value are somewhere in the middle of
      * the valid range. In sRGB this is always a valid value pair, even if
      * the hue changes. Both, lightness and chroma, are linear ranges,
      * so it seems appropriate to have values somewhere in the middle
      * as initial color: The widgets will display the handles somewhere
      * in the middle, which is easier to spot for new users than having
      * them at the very beginning or the very end.
      *
      * The hue range is not linear, but circular – and so are the widgets
      * displaying him: The handle has the same visibility, wherever he is
      * and whatever the hue value is. Therefore, we use 0° as default value
      * which seems to be the natural choice.
      *
      * @note An alternative to 0° might be 180°. If the lightness is 50%,
      * among 0°, 90°, 180° and 270°, it’s 180° that has the lowest possible
      * maximum chroma. So when choose 180°, with a given chroma, the resulting
      * color is more vivid and clean than those at 0°, 90° and 270°. */
     static constexpr LchDouble srgbVersatileInitialColor = {neutralLightness, srgbVersatileChroma, neutralHue};
 
 private:
     /** @brief Delete the constructor to disallow creating an instance
      * of this class. */
     CielchD50Values() = delete;
 };
 
 } // namespace PerceptualColor
 
 #endif // CIELCHD50VALUES_H