utils-math/easing.js at master · kellymilligan/utils-math · GitHub

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/*
    Penner's easing equations adapted to accept a single normalised alpha value
    ---
    a          Number      'alpha' value (from 0-1)
    ---
    Returns    Number      Normalised value with easing applied
*/

// Linear
// ------

export function linear ( a ) {

    return a
  }

  // Sine
  // ----

  export function easeInSine ( a ) {

    return -1 * Math.cos( a * ( Math.PI / 2 ) ) + 1
  }

  export function easeOutSine ( a ) {

    return 1 * Math.sin( a * ( Math.PI / 2 ) )
  }

  export function easeInOutSine ( a ) {

    return -0.5 * ( Math.cos( Math.PI * a / 1 ) - 1 )
  }

  // Quad
  // ----

  export function easeInQuad ( a ) {

    return a * a
  }

  export function easeOutQuad ( a ) {

    return -1 * a * ( a - 2 )
  }

  export function easeInOutQuad ( a ) {

    a /= 0.5
    if ( a < 1 ) return 0.5 * a * a
    a--
    return -0.5 * ( a * ( a - 2 ) - 1 )
  }

  // Cubic
  // -----

  export function easeInCubic ( a ) {

    return a * a * a
  }

  export function easeOutCubic ( a ) {

    a--
    return ( a * a * a + 1 )
  }

  export function easeInOutCubic ( a ) {

    a /= 0.5
    if ( a < 1 ) return 0.5 * a * a * a
    a -= 2
    return 0.5 * ( a * a * a + 2 )
  }

  // Quart
  // -----

  export function easeInQuart ( a ) {

    return a * a * a * a
  }

  export function easeOutQuart ( a ) {

    a--
    return -1 * ( a * a * a * a - 1 )
  }

  export function easeInOutQuart ( a ) {

    a /= 0.5
    if ( a < 1 ) return 0.5 * a * a * a * a
    a -= 2
    return -0.5 * ( a * a * a * a - 2 )
  }

  // Quint
  // -----

  export function easeInQuint ( a ) {

    return a * a * a * a * a
  }

  export function easeOutQuint ( a ) {

    a--
    return a * a * a * a * a + 1
  }

  export function easeInOutQuint ( a ) {

    a /= 0.5
    if ( a < 1 ) return 0.5 * a * a * a * a * a
    a -= 2
    return 0.5 * ( a * a * a * a * a + 2 )
  }

  // Expo
  // ----

  export function easeInExpo ( a ) {

    return Math.pow( 2, 10 * ( a - 1 ) )
  }

  export function easeOutExpo ( a ) {

    return -Math.pow( 2, -10 * a ) + 1
  }

  export function easeInOutExpo  ( a ) {

    a /= 0.5
    if ( a < 1 ) return 0.5 * Math.pow( 2, 10 * ( a - 1 ) )
    a--
    return 0.5 * ( -Math.pow( 2, -10 * a ) + 2 )
  }