You can use a simple multiplier to convert between the two:
/* Using power-of-two because it is exactly representable and makes
the scaling operation (not the rounding!) lossless. The value 1024
preserves roughly three decimal digits. */
double const scale = 1024.0;
// representable range
double const min_value = std::numeric_limits<long>::min() / scale;
double const max_value = std::numeric_limits<long>::max() / scale;
long
to_long(double v)
{
if(v < 0)
{
if(v < min_value)
throw out_of_range();
return static_cast<long>(v * scale - 0.5);
}
else
{
if(v > max_value)
throw out_of_range();
return static_cast<long>(v * scale + 0.5);
}
}
Note that the larger you make the scale, the higher your precision will be, but it also lowers the range. Effectively, this converts a floating-point number into a fixed-point number.
Lastly, you should be able to locate code to compute intersections between line segments using floating-point math easily, so I wonder why you want to use exactly Clipper.