padding for scanlines

[Ank1taS]

@Himanshu40 @chandrakant100 @sabyasachi07 @HembramBeta777 @Tushar7-coder Please discuss more about padding and how used here

        // Determine padding for scanlines
        size_t padding {(4 - (width * sizeof(RGBTRIPLE)) % 4) % 4};

[Ank1taS]

The padding bytes are the bytes following the pixels of a scanline (A scan line is one line, or row, in a raster scanning pattern). Each scan line must end on a 4-byte boundary, so one, two, or three bytes of padding may follow each scan line.
Padding bytes (not necessarily 0) must be appended to the end of the rows in order to bring up the length of the rows to a multiple of four bytes. When the pixel array is loaded into memory, each row must begin at a memory address that is a multiple of 4. This address/offset restriction is mandatory only for Pixel Arrays loaded in memory.
For file storage purposes, only the size of each row must be a multiple of 4 bytes while the file offset can be arbitrary.

for example, A 24-bit bitmap with
Width=1 would have 3 bytes of data per row (blue, green, red) and 1 byte of padding,
Width=2 would have 6 bytes of data and 2 bytes of padding,
Width=3 would have 9 bytes of data and 3 bytes of padding, and
Width=4 would have 12 bytes of data and no padding

However, padding is the same for all the scanlines so it needs to calculate once.

reference : Wikipedia and FileFormat