color.h

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/*
**  color.h
**
**  This is part of Shiokaze, a research-oriented fluid solver for computer graphics.
**  Created by Ryoichi Ando <rand@nii.ac.jp> on Feb 7, 2017.
**
**  Transformed from:
**  https://stackoverflow.com/questions/3018313/algorithm-to-convert-rgb-to-hsv-and-hsv-to-rgb-in-range-0-255-for-both
**
*/
//
#ifndef SHKZ_COLOR_H
#define SHKZ_COLOR_H
//
#include <cmath>
#include <ostream>
#include <vector>
#include <shiokaze/core/common.h>
//
SHKZ_BEGIN_NAMESPACE
//
class color {
public:
    struct rgb {
        double r;
        double g;
        double b;
    };
    struct hsv {
        double h;
        double s;
        double v;
    };
    static hsv rgb2hsv(rgb in) {
        hsv         out;
        double      min, max, delta;
 
        min = in.r < in.g ? in.r : in.g;
        min = min  < in.b ? min  : in.b;
 
        max = in.r > in.g ? in.r : in.g;
        max = max  > in.b ? max  : in.b;
 
        out.v = max;                                // v
        delta = max - min;
        if( max > 0.0 ) { // NOTE: if Max is == 0, this divide would cause a crash
            out.s = (delta / max);                  // s
        } else {
            // if max is 0, then r = g = b = 0
            // s = 0, v is undefined
            out.s = 0.0;
            out.h = NAN;                            // its now undefined
            return out;
        }
        if( in.r >= max )                           // > is bogus, just keeps compilor happy
            out.h = ( in.g - in.b ) / delta;        // between yellow & magenta
        else
            if( in.g >= max )
                out.h = 2.0 + ( in.b - in.r ) / delta;  // between cyan & yellow
            else
                out.h = 4.0 + ( in.r - in.g ) / delta;  // between magenta & cyan
 
        out.h *= 60.0;                              // degrees
 
        if( out.h < 0.0 )
            out.h += 360.0;
 
        return out;
    }
    static rgb hsv2rgb(hsv in) {
        double      hh, p, q, t, ff;
        long        i;
        rgb         out;
 
        if(in.s <= 0.0) {       // < is bogus, just shuts up warnings
            out.r = in.v;
            out.g = in.v;
            out.b = in.v;
            return out;
        }
        hh = in.h;
        if(hh >= 360.0) hh = 0.0;
        hh /= 60.0;
        i = (long)hh;
        ff = hh - i;
        p = in.v * (1.0 - in.s);
        q = in.v * (1.0 - (in.s * ff));
        t = in.v * (1.0 - (in.s * (1.0 - ff)));
 
        switch(i) {
            case 0:
                out.r = in.v;
                out.g = t;
                out.b = p;
                break;
            case 1:
                out.r = q;
                out.g = in.v;
                out.b = p;
                break;
            case 2:
                out.r = p;
                out.g = in.v;
                out.b = t;
                break;
 
            case 3:
                out.r = p;
                out.g = q;
                out.b = in.v;
                break;
            case 4:
                out.r = t;
                out.g = p;
                out.b = in.v;
                break;
            case 5:
            default:
                out.r = in.v;
                out.g = p;
                out.b = q;
                break;
        }
        return out;
    }
    static void heatcolor( double heat, double rgb_result[3] ) {
        hsv hsv_color;
        heat = std::min(1.0,std::max(0.0,heat));
        hsv_color.h = 230.0 * (1.0-heat);
        hsv_color.s = 0.5;
        hsv_color.v = 0.8;
        rgb rgb_color = color::hsv2rgb(hsv_color);
        rgb_result[0] = rgb_color.r;
        rgb_result[1] = rgb_color.g;
        rgb_result[2] = rgb_color.b;
    }
};
//
SHKZ_END_NAMESPACE
#endif