int v =
      ((r << 24) & 0xff000000) |
      ((g << 16) &   0xff0000) |
      ((b <<  8) &     0xff00) |
      ( a        &       0xff) ;

Is there a reason you're doing the shift before the mask? I find this much less intuitive than the equivalent

    int v =
      ((r & 0xff) << 24) |
      ((g & 0xff) << 16) |
      ((b & 0xff) <<  8) |
      ( a & 0xff) ;