Trying to work by the design guidelines for GIL, I use bits__ for my channel data types. I often have external data I’m wrapping into GIL image views. However, even using the bits__ types for data pointers, I have to add in a reinterpret_cast before I can create my image views. Take the following code
int width = 3;
int height = 2;
boost::gil::bits8 data8[] = {0, 1, 100, 200, 50, 51};
boost::gil::bits8* pBits8 = data8;
boost::gil::gray8_ptr_t pGray8 = pBits8;
boost::gil::gray8_view_t v = interleaved_view(width, height, pGray8, width * sizeof(boost::gil::bits8));
Results in the error on line 6 “error C2440: ‘initializing’ : cannot convert from ‘boost::gil::bits8 *’ to ‘boost::gil::gray8_ptr_t’
1> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast”
Delving into the source code as much as I can, it appears these types really are unreleated. bits8 is just unsigned char, but gray8_ptr_t is a pointer to a struct pixel<bits8,gray_layout_t>. The only element of this struct is a single bits8, so a reinterpret_cast looks safe. It also works fine for the tests I’ve thrown at it.
However, I wrap external data into image views quite often, and having a reinterpret_cast in every place feels problematic. Is there a safer way of constructing a pixel pointer for use in GIL?
Current workaround:
template<class Dest, class Src>
Dest gil_safe_ptr_cast(Src src)
{
// this cast is unsafe, use reinterpret_cast
BOOST_STATIC_ASSERT(false);
}
template<> boost::gil::gray8_ptr_t gil_safe_ptr_cast(boost::gil::bits8* pBits8)
{
return reinterpret_cast<boost::gil::gray8_ptr_t>(pBits8);
}
boost::gil::bits8* pBits8 = data8;
boost::gil::gray8_ptr_t pGray8 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits8); // works
boost::gil::bits16* pBits16 = NULL;
boost::gil::gray8_ptr_t pGray82 = gil_safe_ptr_cast<boost::gil::gray8_ptr_t>(pBits16); // compile error as expected
1 Answer