I have packed data of rgba values in an 16 bit short, so for each channel goes 4bit, how can I change specific channel only, lets say I want to change red channel to it's value devided by two. I know how to change specific bits in an int but changing bit by bit would be very slow and tiresome.
So in code First I save RGBA values in a short:
RGBA = R | (G << 4) | (B << 8) | (A << 12) Then I want to change 'A' part of the RGBA short to A / 2.
If you don't care about the order of the bits (for example, don't need that for serialisation purposes), then this is a good use case for bitfields. Example:
struct RGBA { std::uint16_t r : 4; std::uint16_t g : 4; std::uint16_t b : 4; std::uint16_t a : 4; }; RGBA rgba = {r, g, b, a}; a = rgba.a; // read a from rgba If you do need to have a std::uint16_t with the bits in particular order, then you can use the bitwise operators instead.
So in code First I save RGBA values in a short:
RGBA = R | (G << 4) | (B << 8) | (A << 12)Then I want to 'A' part of the RGBA short
Like this:
A = (RGBA >> 12) && 0xF; You technically don't need the masking in the case of A because it's going to be zeroes, but you do need it for all others to mask out the higher bits.
Sorry I was unclear what I was asking, I figured it out, I just have to get A value from RGBA as eerorika said and save it to another short called Aval:
unsigned short Aval = RGBA >> 12; then reset A part of RGBA to 0 so:
RGBA &= (0xF << 12); and then change Aval to whatever you want and then save it to RGBA short's A part:
RGBA |= Aval << 12;