planetsim/src/render/Colors.cpp

#include "Colors.hpp"
#include <algorithm>
#include <cmath>

Color elevationColor(double e, double seaLevel) {
    if (e < seaLevel) {
        // Water: deep -> shallow blue.
        double t = std::clamp((e + 11000.0) / (seaLevel + 11000.0), 0.0, 1.0);
        return Color{ (unsigned char)(10 + 20 * t),
                      (unsigned char)(30 + 90 * t),
                      (unsigned char)(80 + 120 * t), 255 };
    }
    // Land: green -> brown -> white by height.
    double t = std::clamp(e / 9000.0, 0.0, 1.0);
    if (t < 0.4) { double u = t / 0.4;
        return Color{ (unsigned char)(60 + 80 * u), (unsigned char)(140 - 30 * u),
                      (unsigned char)(50), 255 }; }
    if (t < 0.75) { double u = (t - 0.4) / 0.35;
        return Color{ (unsigned char)(140 - 30 * u), (unsigned char)(110 - 40 * u),
                      (unsigned char)(50 + 10 * u), 255 }; }
    double u = (t - 0.75) / 0.25;
    return Color{ (unsigned char)(110 + 145 * u), (unsigned char)(70 + 185 * u),
                  (unsigned char)(60 + 195 * u), 255 };
}

Color plateColor(int id) {
    float h = std::fmod(id * 0.61803398875f, 1.0f) * 360.0f;
    return ColorFromHSV(h, 0.65f, 0.85f);
}

Color ageColor(double age, double maxAge) {
    double t = std::clamp(age / std::max(1.0, maxAge), 0.0, 1.0);
    return Color{ (unsigned char)(40 + 200 * t), (unsigned char)(40),
                  (unsigned char)(200 - 160 * t), 255 };
}

Color crustColor(bool oceanic) {
    return oceanic ? Color{ 30, 60, 160, 255 }     // oceanic: deep blue
                   : Color{ 160, 130, 70, 255 };    // continental: warm brown
}

Color lakeColor() { return Color{ 40, 200, 210, 255 }; }   // bright turquoise (vs ocean blue)

Color biomeColor(Biome b) {
    switch (b) {
        case Biome::Ocean:     return Color{  20,  60, 120, 255 };  // deep blue
        case Biome::Ice:       return Color{ 235, 240, 250, 255 };  // white (polar caps / snow)
        case Biome::Lake:      return Color{  40, 200, 210, 255 };  // bright turquoise
        case Biome::Beach:     return Color{ 222, 210, 150, 255 };  // pale sand
        case Biome::Wetland:   return Color{  70, 115,  95, 255 };  // dark teal-green (swamp/bayou)
        case Biome::Grassland: return Color{ 130, 185,  80, 255 };  // light green
        case Biome::Savanna:   return Color{ 185, 180,  85, 255 };  // yellow-green
        case Biome::Desert:    return Color{ 214, 184, 120, 255 };  // tan
        case Biome::Forest:    return Color{  40, 110,  50, 255 };  // dark green
        case Biome::Taiga:     return Color{  55, 105,  85, 255 };  // blue-green (boreal)
        case Biome::Tundra:    return Color{ 155, 165, 150, 255 };  // pale grey-green
        case Biome::Hills:     return Color{ 120, 135,  70, 255 };  // olive
        case Biome::Mountains: return Color{ 135, 125, 115, 255 };  // grey-brown
    }
    return Color{ 255, 0, 255, 255 };   // unreachable; flags an unmapped biome
}

const char* biomeName(Biome b) {
    switch (b) {
        case Biome::Ocean:     return "Ocean";
        case Biome::Ice:       return "Ice cap";
        case Biome::Lake:      return "Lake";
        case Biome::Beach:     return "Beach";
        case Biome::Wetland:   return "Wetland";
        case Biome::Grassland: return "Grassland";
        case Biome::Savanna:   return "Savanna";
        case Biome::Desert:    return "Desert";
        case Biome::Forest:    return "Forest";
        case Biome::Taiga:     return "Taiga";
        case Biome::Tundra:    return "Tundra";
        case Biome::Hills:     return "Hills";
        case Biome::Mountains: return "Mountains";
    }
    return "?";
}

const char* colorModeName(ColorMode m) {
    switch (m) {
        case ColorMode::Elevation:   return "Elevation";
        case ColorMode::Plate:       return "Plates";
        case ColorMode::Age:         return "Crust age";
        case ColorMode::Crust:       return "Crust type";
        case ColorMode::Biome:       return "Biome";
        case ColorMode::Temperature: return "Temperature";
        case ColorMode::Precip:      return "Precipitation";
    }
    return "?";
}

// Temperature ramp over ~[-40, 40] C: deep blue -> cyan -> green -> yellow -> red.
Color tempColor(double celsius) {
    double t = std::clamp((celsius + 40.0) / 80.0, 0.0, 1.0);   // 0 cold .. 1 hot
    // 4 segments between 5 control colors.
    static const unsigned char key[5][3] = {
        {  30,  40, 130 },  // -40 C  deep blue
        {  60, 160, 210 },  // -20 C  cyan
        {  90, 190,  90 },  //   0 C  green
        { 225, 200,  70 },  // +20 C  yellow
        { 210,  70,  50 },  // +40 C  red
    };
    double s = t * 4.0; int k = std::min(3, (int)s); double f = s - k;
    auto L = [&](int c){ return (unsigned char)(key[k][c] + (key[k + 1][c] - key[k][c]) * f); };
    return Color{ L(0), L(1), L(2), 255 };
}

// Precipitation ramp over normalized [0,1]: tan (dry) -> green -> teal/blue (wet).
Color precipColor(double moist01) {
    double t = std::clamp(moist01, 0.0, 1.0);
    static const unsigned char key[4][3] = {
        { 205, 180, 120 },  // 0.00  dry tan
        { 170, 185,  90 },  // 0.33  scrub
        {  70, 160,  90 },  // 0.66  green
        {  40, 120, 190 },  // 1.00  wet blue
    };
    double s = t * 3.0; int k = std::min(2, (int)s); double f = s - k;
    auto L = [&](int c){ return (unsigned char)(key[k][c] + (key[k + 1][c] - key[k][c]) * f); };
    return Color{ L(0), L(1), L(2), 255 };
}