the macro is ENABLE_BILINEAR, and could just as well disable the entire function (or, even BE a macro, to avoid the additional function calls it needs per pixel as a function, but that would need some profiling before we bother about).

#ifdef ENABLE_BILINEAR
void copyPixelBilinear(...) {
...
}
#endif

#ifndef ENABLE_BILINEAR
void copyPixelNearest(...) {
...
}
#endif

is what I'm talking about (completely removing the unused function basically.) But it's not super-critical.