BMP image format writing helper

main.cpp

#include <vector>
#include <cstdint>
#include <iostream>
using namespace std;

class BitmapWriter
{
public:

    struct RGB { unsigned char red; unsigned char green; unsigned char blue;
                 RGB(double r, double g, double b) : red((unsigned char)(r*256)), green((unsigned char)(g*256)), blue((unsigned char)(b*256)) {}
               };

    friend ostream& operator << (ostream& s, const BitmapWriter& b)
    {
        char byte;
        uint16_t word;
        uint32_t dword;

#define raw_write(var,value) var = value; s.write(reinterpret_cast<char*>(&var),sizeof(var));

        // HEADER
        raw_write(byte,'B');
        raw_write(byte,'M');
        raw_write(dword,b.p_data.size()*3);
        raw_write(word,0);
        raw_write(word,0);
        raw_write(dword,0x36);

        // INFO
        raw_write(dword,sizeof(dword)*9+sizeof(word)*2);
        raw_write(dword,b.p_x);
        raw_write(dword,b.p_y);
        raw_write(word,1);
        raw_write(word,24);
        raw_write(dword,0);
        raw_write(dword,0);
        raw_write(dword,0x0ec4);
        raw_write(dword,0x0ec4);
        raw_write(dword,0);
        raw_write(dword,0);

        // DATA
        size_t padding = (4-(b.p_x*3%4))%4;

        for (size_t i = 0; i < b.p_y; i++)
        {
            for (size_t j = 0; j < b.p_x; j++)
            {
                raw_write(byte,b.p_data[i*b.p_x+j].blue);
                raw_write(byte,b.p_data[i*b.p_x+j].green);
                raw_write(byte,b.p_data[i*b.p_x+j].red);

            }
            for (size_t j = 0; j < padding; j++)
            {
                raw_write(byte,0);
            }
        }
#undef raw_write
        return s;
    }

    BitmapWriter(const vector<RGB>& data, size_t x, size_t y) : p_data(data), p_x(x), p_y(y) {}

private:
    const vector<RGB>& p_data;
    size_t p_x;
    size_t p_y;
};

/* Conversion routine from HSV color space to RGB */
BitmapWriter::RGB hsv2rgb(double h, double s, double v)
{
    if (s <= 0)
    {
        if (std::isnan(h))
        {
            return BitmapWriter::RGB(v,v,v);
        }
        else
        {
            return BitmapWriter::RGB(0,0,0);
        }
    }
    else
    {
        double hh = h;
        if (hh >= 360) hh = 0;
        hh /= 60;

        short i = (short)hh;

        double ff = hh - i;

        double p = v * (1.0-s);
        double q = v * (1.0 - (s * ff));
        double t = v * (1.0 - (s * (1.0 - ff)));

        switch (i)
        {
        case 0:
            return BitmapWriter::RGB(v,t,p);
        case 1:
            return BitmapWriter::RGB(q,v,p);
        case 2:
            return BitmapWriter::RGB(p,v,t);
        case 3:
            return BitmapWriter::RGB(p,q,v);
        case 4:
            return BitmapWriter::RGB(t,p,v);
        case 5:
        default:
            return BitmapWriter::RGB(v,p,q);
        }
    }
}