Don't understand RGB macro declaration in Win32 API.

It creates a "24 bit color reference" in 32 bit integer / unsigned in the form of "0x00bbggrr"

Red is the low 8 bits (0-7), Green is the next 8 bits (8-15) and Blue is the next 8 bits (16-23).

All the "typcasting" is to instruct the compiler how to do the math (shifts) on the values. The parenthesis around (r), (g), and (b) is so you can use an "expression" as the argument and it will be treated properly.

It might be a fun exercise for you to spread this statement out and slowly remove the sub-expressions to see how the parenthesises (parenthesii?) wrap the pieces to be evaluated by the compiler. Then it might make more sense to you.

One last thing, for "#define" macros, parenthesis are used to provide clarity to the compiler, which, ironically, removes clarity for the human (you).

It just composes a 32-bit value from the three components r, g, and b. Here is it step by step. First let's take the outer parentheses and cast to COLORREF away:

(((BYTE)(r)|((WORD)((BYTE)(g))<<8))|(((DWORD)(BYTE)(b))<<16))

The r value is just reduced to 8-bits by the cast to BYTE and copied into the lower 8 bits:

(BYTE)(r)

The green value is also masked by its lower 8 bits, then cast into 16-bits (which is unnecessary) and shifted 8 bits to the left so that the green component now occupies bits 8...15:

((WORD)((BYTE)(g))<<8)

Both components are bitwise or-ed together:

((BYTE)(r)|((WORD)((BYTE)(g))<<8))

Finally the blue values is masked to 8 bits, cast up to 32-bit (again unnecessary) and shifted 16 bits to the left such that the blue component occupies now bits 16...23:

(((DWORD)(BYTE)(b))<<16)

Then it's combined to the red and green combined value that we did in the previous step. So we end up with

red:   bits 0...7
green: bits 8...15
blue:  bits 16...23

Easy, wasn't it.