gistfile1.cpp

struct VolumeVal {
    uint16_t type;
    float field;
};

using fieldfn_t = std::function<float(const vec3 &)>;
using volfn_t = std::function<VolumeVal(const vec3 &)>;

// Result is a function giving one of three possible results:
// the result of fnb (preexisting layers)
// {type, fna(pt)} (new layer)
// {kAirVolume, 1.0f}
template<typename fna_t>
auto layer(uint16_t type, const fna_t & fna, const volfn_t & fnb) -> volfn_t
{
    return [=](const vec3 & pt){
        auto f = fnb(pt);
        if(f.field <= 0.0f)
            return f;
        
        auto f2 = fna(pt);
        return (f2 <= 0.0f)? VolumeVal{type, f2} : VolumeVal{kAirVolume, 1.0f};
    };
}

template<typename fn_t>
auto turbulate(const vec3 & scl, const vec3 & amp, const fn_t & fn) -> volfn_t
{
    return [=](const vec3 & pt){
        vec3 turbPtX = pt/scl + vec3{0, 0, 1000};
        vec3 turbPtY = turbPtX + vec3{1000, 0, 0};
        vec3 turbPtZ = turbPtX + vec3{0, 1000, 0};
        return fn(pt + vec3{glm::simplex(turbPtX), glm::simplex(turbPtY), glm::simplex(turbPtZ)}*amp);
    };
}

auto plane(float y, float yscl) -> fieldfn_t {
    return [=](const vec3 & pt){return (pt.y - y)/yscl;};
}

int main(int argc, const char * argv[])
{
    uint32_t colors[] = {
        0x00FFFFFF,
        0x00880000,
        0x00008800,
        0x00000088
    };
    
    volfn_t volfn = [](const vec3 &){return VolumeVal{kAirVolume, 1.0f};};
    
    volfn = layer(1, plane(0.0f, 100.0f), volfn);
    volfn = turbulate(vec3{100.0f}, vec3{10.0f}, volfn);
    volfn = layer(2, plane(32.0f, 100.0f), volfn);
    volfn = turbulate(vec3{100.0f}, vec3{10.0f}, volfn);
    volfn = layer(3, plane(40.0f, 100.0f), volfn);
    volfn = turbulate(vec3{100.0f}, vec3{10.0f}, volfn);
    
    SimpleImage output(1024, 512, 3);
    for(int ix = 0; ix < output.width; ++ix)
    for(int iy = 0; iy < output.height; ++iy)
    {
        float x = ix, y = iy - output.height/2.0f;
        VolumeVal val = volfn(vec3{x, y, 0.5f});
        output.SetPixelRGB(ix, iy, colors[val.type]);
    }
    TargaFileInfo::Write("testout.tga", output);
    return EXIT_SUCCESS;
}