Keyframe sprite animation technique

gistfile1.scss

@include create-keyframe(sprite_animation) {
    $frames:20;
    $step:100%/$frames;
    $pre_step:$step - 0.0001%;

    @for $i from 0 through $frames {
        $n: ($i * $step);
        $n2: ($n + $pre_step);
        #{$n}, #{$n2} { @include get-sprite($animations_sprite, sequence_#{$i}) }
    }
    100% {@include get-sprite($animations_sprite,  sequence_#{$frames})}
}