NavigationPagerStyleInterpolator.js

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * Facebook, Inc. ("Facebook") owns all right, title and interest, including
 * all intellectual property and other proprietary rights, in and to the React
 * Native CustomComponents software (the "Software").  Subject to your
 * compliance with these terms, you are hereby granted a non-exclusive,
 * worldwide, royalty-free copyright license to (1) use and copy the Software;
 * and (2) reproduce and distribute the Software as part of your own software
 * ("Your Software").  Facebook reserves all rights not expressly granted to
 * you in this license agreement.
 *
 * THE SOFTWARE AND DOCUMENTATION, IF ANY, ARE PROVIDED "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES (INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE) ARE DISCLAIMED.
 * IN NO EVENT SHALL FACEBOOK OR ITS AFFILIATES, OFFICERS, DIRECTORS OR
 * EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THE SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @providesModule NavigationPagerStyleInterpolator
 * @flow
 */
'use strict';

import type  {
  NavigationSceneRendererProps,
} from 'NavigationTypeDefinition';

/**
 * Utility that builds the style for the card in the cards list.
 *
 * +-------------+-------------+-------------+
 * |             |             |             |
 * |             |             |             |
 * |             |             |             |
 * |    Next     |   Focused   |  Previous   |
 * |    Card     |    Card     |    Card     |
 * |             |             |             |
 * |             |             |             |
 * |             |             |             |
 * +-------------+-------------+-------------+
 */

/**
 * Render the initial style when the initial layout isn't measured yet.
 */
function forInitial(props: NavigationSceneRendererProps): Object {
  const {
    navigationState,
    scene,
  } = props;

  const focused = navigationState.index === scene.index;
  const opacity = focused ? 1 : 0;
  // If not focused, move the scene to the far away.
  const dir = scene.index > navigationState.index ? 1 : -1;
  const translate = focused ? 0 : (1000000 * dir);
  return {
    opacity,
    transform: [
      { translateX: translate },
      { translateY: translate },
    ],
  };
}

function forHorizontal(props: NavigationSceneRendererProps): Object {
  const {
    layout,
    position,
    scene,
  } = props;

  if (!layout.isMeasured) {
    return forInitial(props);
  }

  const index = scene.index;
  const inputRange = [index - 1, index, index + 1];

  const width = layout.initWidth;
  const translateX = position.interpolate({
    inputRange,
    outputRange: [width, 0, -width],
  });

  return {
    opacity : 1,
    shadowColor: 'transparent',
    shadowRadius: 0,
    transform: [
      { scale: 1 },
      { translateX },
      { translateY: 0 },
    ],
  };
}

module.exports = {
  forHorizontal,
};