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                <h1>Easing settings</h1>

  As you resize the window width between 400px and 1400px, you'll see the values move from 0 to 100. With linear easing, they move in a predictable, smooth way, but the "in" easing values slowly accelerate while the "out" ones slowly decelerate. These settings are useful for tuning values like font-size which can create layout problems if they get too large too quickly.

  <li class="linear"></li>
  <li class="in-quad"></li>
  <li class="in-cubic"></li>
  <li class="in-quart"></li>
  <li class="in-quint"></li>
  <li class="out-quad"></li>
  <li class="out-cubic"></li>
  <li class="out-quart"></li>
  <li class="out-quint"></li>



                // strip-units required by spread mixin
@function strip-units($number)
  @return $number / ($number * 0 + 1)

// pow and sqrt required by ease function
// adapted from
@function pow($base, $exponent)
  $value: $base
  @if $exponent > 1
    @for $i from 2 through $exponent
      $value: $value * $base
  @if $exponent < 1
    @for $i from 0 through -$exponent
      $value: $value / $base
  @return $value

@function sqrt($number)
  $root: 4
  @for $i from 1 through 50
    $root: $root - (pow($root, 2) - $number) / (2 * $root)
  @return $root

// adapted from
@function ease($iteration, $start-value, $change, $total-iterations, $ease)
  $progress: $iteration / $total-iterations

  // value increases evenly
  @if $ease == linear
    @return $change * $progress + $start-value

  // value increases on a curve, accelerating
  @if $ease == in-quad
    @return $change * $progress * $progress + $start-value

  // value increases on a curve, decelerating
  @if $ease == out-quad
    @return -$change * $progress * ($progress - 2) + $start-value

  // value accelerates sharply
  @if $ease == in-cubic
    @return $change * pow($progress, 3) + $start-value

  // value decelerates sharply
  @if $ease == out-cubic
    @return $change * (pow($progress - 1, 3) + 1) + $start-value

  // value accelerates more sharply
  @if $ease == in-quart
    @return $change * pow($progress, 4) + $start-value

  // value decelerates more sharply
  @if $ease == out-quart
    @return -$change * (pow($progress - 1, 4) - 1) + $start-value

  // value accelerates very sharply
  @if $ease == in-quint
    @return $change * pow($progress, 5) + $start-value

  // value decelerates very sharply
  @if $ease == out-quint
    @return $change * (pow($progress - 1, 5) + 1) + $start-value

// spreads a property value from min to max across media queries
//   $property:      CSS property to set
//   $property-min:  min value of the property
//   $property-max:  max value of the property
//   $dimension:     media query dimension - either min-width or min-height
//   $dimension-min: first media query of the chosen dimension
//   $dimension-max: final media query of the chosen dimension
//   $default-value: true/false (defaults to true).
//                   Should a default value (min for min-width/height,
//                   max for max-width/height) be included outside the query?
//   $precision:     how many pixels each media query should cover
//   $ease:          easing function to use when calculating value
//                   helpful for fine-tuning some widths in the mid-range
=spread($property, $property-min, $property-max, $dimension: min-width, $dimension-min: 400px, $dimension-max: 1400px, $default-value: true, $precision: 50px, $ease: linear)
  $total-iterations: abs(strip-units(ceil(($dimension-max - $dimension-min) / $precision))) - 1
  $max-dimension:    $dimension == max-width or $dimension == max-height

  @if $default-value
    #{$property}: if($max-dimension, $property-max, $property-min)

  @for $iteration from 0 through $total-iterations
    $iteration: if($max-dimension, $total-iterations - $iteration, $iteration)
    @media (#{$dimension}: $dimension-min + ($iteration * $precision))
      #{$property}: ease($iteration, $property-min, $property-max - $property-min, $total-iterations, $ease)

// demo styles
  font-family: sans-serif
  line-height: 1.5
  margin: 25px

  +spread(font-size, 20px, 35px)
  font-weight: bold

  background: #eee
  border: #ccc 1px solid

  margin: 0
  padding: 0

  font-size: 14px
  list-style-type: none
  margin: 0 0 10px
  padding: 5px
  white-space: nowrap

// debugging
=spread-debug($ease: linear)
  $min: 1
  $max: 100
  $start: 400px
  $end: 1400px
  $precision: 10px

  width: #{$min}px

    display: block
    content: '#{$ease}: #{$min}'

  $total-iterations: strip-units(ceil(($end - $start) / $precision)) - 1

  @for $iteration from 0 through $total-iterations
    @media (min-width: $start + ($iteration * $precision))
      width: percentage(ease($iteration, $min, $max - $min, $total-iterations, $ease: $ease) / 100)

        content: '#{$ease}: #{ease($iteration, $min, $max - $min, $total-iterations, $ease: $ease)}'