I'm trying to use partial template specialization on a (non-member) function, and I'm tripping up on the syntax. I've searched StackOverflow for other partial template specialization questions, but those deal with partial specialization of a class or member function template.
For a starting point, I have:
struct RGBA {
RGBA(uint8 red, uint8 green, uint8 blue, uint8 alpha = 255) :
r(red), g(green), b(blue), a(alpha)
{}
uint8 r, g, b, a;
};
struct Grayscale {
Grayscale(uint8 intensity) : value(intensity) {}
uint8 value;
};
inline uint8 IntensityFromRGB(uint8 r, uint8 g, uint8 b) {
return static_cast<uint8>(0.30*r + 0.59*g + 0.11*b);
}
// Generic pixel conversion. Must specialize this template for specific
// conversions.
template <typename InType, typename OutType>
OutType ConvertPixel(InType source);
I can do a complete specialization of ConvertPixel to make an RGBA to Grayscale conversion function like this:
template <>
Grayscale ConvertPixel<RGBA, Grayscale>(RGBA source) {
return Grayscale(IntensityFromRGB(source.r, source.g, source.b));
}
I'll conceivably have more pixel types that offer red, green, and blue, but perhaps in a different format, so what I'd really like to do is a partial specialization by specifying Grayscale
for OutType
and still allow for a variety of InType
s. I've tried a variety of approaches like this:
template <typename InType>
Grayscale ConvertPixel<InType, Grayscale>(InType source) {
return Grayscale(IntensityFromRGB(source.r, source.g, source.b));
}
But the (Microsoft VS 2008 C++) compiler rejects it.
Is what I'm attempting possible? If so, what's the right syntax?