Sass matrix rotation (doesn't quite work)

matrix-rotation-spinner.scss

// Matrix rotation version:
//   this would work, except the y-axis is fliped for box-shadow
$m-0-degrees: ((1, 0), (0, 1));
$m-90-degrees: ((0, 1), (-1, 0));
$m-180-degrees: ((-1, 0), (0, -1));
$m-270-degrees: ((0, -1), (1, 0));

@function m-rotate($x, $y, $m) {
  $m1: nth($m, 1);
  $m2: nth($m, 2);
  @return nth($m1, 1)*$x+nth($m1, 2)*$x nth($m2, 1)*$y+nth($m2, 2)*$y;
}

@mixin shadow-dots($mx, $color1, $color2, $size) {
  box-shadow:
    m-rotate(15px, 15px, $mx) red,
    m-rotate(15px, -15px, $mx) blue,
    m-rotate(-15px, -15px, $mx) green,
    m-rotate(-15px, 15px, $mx) yellow;
}

@mixin shadow-dots($x, $y, $x2, $y2, $color1, $color2, $size) {
  box-shadow:
    ($size*$x)+($size*$x2) ($size*$y)+($size*$y2) $color2,
    ($size*$x)+($size*$x2) ($size*$y*-1)+($size*$y2*-1) $color1,
    ($size*$x*-1)+($size*$x2*-1) ($size*$y*-1)+($size*$y2*-1) $color2,
    ($size*$x*-1)+($size*$x2*-1) ($size*$y)+($size*$y2) $color1;
}

@keyframes spin {
  0%, 100% {
    @include shadow-dots($m-0-degrees, $spinnerColor, $spinnerColor2, $spinnerSize);
  }
  25% {
    @include shadow-dots($m-90-degrees, $spinnerColor2, $spinnerColor, $spinnerSize);
  }
  50% {
    @include shadow-dots($m-180-degrees, $spinnerColor, $spinnerColor2, $spinnerSize);
  }
  75% {
    @include shadow-dots($m-270-degrees, $spinnerColor2, $spinnerColor, $spinnerSize);
  }
}