<!DOCTYPE html>
<meta charset=utf-8>
<title>The effect value of a keyframe effect: Calculating the transformed
  distance between keyframes</title>
<link rel="help" href="https://drafts.csswg.org/web-animations/#the-effect-value-of-a-keyframe-animation-effect">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../../testcommon.js"></script>
<script src="../../resources/easing-tests.js"></script>
<body>
<div id="log"></div>
<script>
'use strict';

// Test that applying easing to keyframes is applied as expected

for (const params of gEasingTests) {
  test(t => {
    const target = createDiv(t);
    const anim   = target.animate([ { width: '0px' },
                                    // We put the easing on the second keyframe
                                    // so we can test that it is only applied
                                    // to the specified keyframe.
                                    { width: '100px', easing: params.easing },
                                    { width: '200px' } ],
                                  { duration: 2000,
                                    fill: 'forwards' });

    for (const sampleTime of [0, 999, 1000, 1100, 1500, 2000]) {
      anim.currentTime = sampleTime;

      const portion = (sampleTime - 1000) / 1000;
      const expectedWidth = sampleTime < 1000
                            ? sampleTime / 10 // first segment is linear
                            : 100 + params.easingFunction(portion) * 100;
      assert_approx_equals(parseFloat(getComputedStyle(target).width),
                           expectedWidth,
                           0.02,
                           'The width should be approximately ' +
                           `${expectedWidth} at ${sampleTime}ms`);
    }
  }, `A ${params.desc} on a keyframe affects the resulting style`);
}

// Test that a linear-equivalent cubic-bezier easing applied to a keyframe does
// not alter (including clamping) the result.

for (const params of gEasingTests) {
  const linearEquivalentEasings = [ 'cubic-bezier(0, 0, 0, 0)',
                                    'cubic-bezier(1, 1, 1, 1)' ];
  test(t => {
    for (const linearEquivalentEasing of linearEquivalentEasings) {
      const timing = { duration: 1000,
                       fill: 'forwards',
                       easing: params.easing };

      const linearTarget = createDiv(t);
      const linearAnim = linearTarget.animate([ { width: '0px' },
                                                { width: '100px' } ],
                                              timing);

      const equivalentTarget = createDiv(t);
      const equivalentAnim =
        equivalentTarget.animate([ { width: '0px',
                                     easing: linearEquivalentEasing },
                                   { width: '100px' } ],
                                 timing);

      for (const sampleTime of [0, 250, 500, 750, 1000]) {
        linearAnim.currentTime = sampleTime;
        equivalentAnim.currentTime = sampleTime;

        assert_equals(getComputedStyle(linearTarget).width,
                      getComputedStyle(equivalentTarget).width,
                      `The 'width' of the animated elements should be equal ` +
                      `at ${sampleTime}ms`);
      }
    }
  }, 'Linear-equivalent cubic-bezier keyframe easing applied to an effect ' +
     `with a ${params.desc} does not alter the result`);
}

</script>
</body>
