Function blend_channel_nonpremult

fn blend_channel_nonpremult(
    src: u32,
    src_a: u8,
    dst: u32,
    dst_a: u8,
    scale: u32,
    shift: u32,
) -> u8

Blend a single channel of src over dst, given their alpha channel values. src and dst are assumed to be NOT pre-multiplied by alpha.