translating shifts from Java (Processing) to C++ (arduino)

Using Arduino Programming Questions
21

If I understand the basis of your original question you wish to convert a source pixel buffer of 'rrrrrggggggbbbbb' values to a gray scale equivalent destination pixel buffer.

The following code fragment should accomplish that ...

struct rgb_t
{
    union {
        struct {
            unsigned _b:5;
            unsigned _g:6;
            unsigned _r:5;
        };
        uint16_t    _rgb;
    };
    
    rgb_t(uint8_t r, uint8_t g, uint8_t b)
        : _r(r), _g(g), _b(b)
    {}
    
    rgb_t(uint16_t rgb)
        : _rgb(rgb)
    {}

    operator uint16_t() const { return _rgb; };
    uint8_t red()   const     { return _r;   };
    uint8_t green() const     { return _g;   };
    uint8_t blue()  const     { return _b;   };
};


uint8_t bufSrc[32];    // color pixel buffer
uint8_t bufDst[32];    // gray scale buffer

// convert the color pixel buffer 'bufSrc' to an average gray scale pixel buffer 'bufDst'

rgb_t* pSrc = (rgb_t*)bufSrc;
rgb_t* pDst = (rgb_t*)bufDst;

for (uint16_t i = sizeof(bufSrc) / 2; i--; )
{
    rgb_t    pixelSrc = *pSrc++;
    uint8_t  average  = (pixelSrc.red() + (pixelSrc.green() >> 1) + pixelSrc.blue());
    *pDst++ = rgb_t(average, average << 1, average);
}