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Copyright (c) 2015 The Chromium Authors. All rights reserved.
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
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<link rel="import" href="/base/base.html">

<script>
'use strict';

tv.exportTo('tv.c.tracks', function() {

  /**
   * A helper object encapsulating all parameters necessary to draw a chart
   * series and provides conversion between world coordinates and physical
   * pixels.
   *
   * All parameters (except for pixelRatio) are assumed to be in physical pixels
   * (i.e. already pre-multiplied with pixelRatio).
   *
   * The diagram below explains the meaning of the resulting fields with
   * respect to a chart track:
   *
   *      outerTopViewY -> +--------------------/-\-------+ <- Top padding
   *      innerTopViewY -> + - - - - - - - - - -| |- - - -+ <- Axis max
   *                       | ..               ==\-/==     |
   *                       |   ==       Series       ==   |
   *                       |     ==/-\==               .. |
   *   innerBottomViewY -> + - - -Point- - - - - - - - - -+ <- Axis min
   *   outerBottomViewY -> +-------\-/--------------------+ <- Bottom padding
   *                       ^                              ^
   *                   leftViewX                      rightViewX
   *                 leftTimeStamp                  rightTimestamp
   *
   * Labels starting with a lower case letter are the resulting fields of the
   * transform object. Labels starting with an upper case letter correspond
   * to the relevant chart track concepts.
   *
   * @constructor
   */
  function ChartTransform(displayTransform, axis, trackWidth,
      trackHeight, topPadding, bottomPadding, pixelRatio) {
    this.pixelRatio = pixelRatio;

    // X axis.
    this.leftViewX = 0;
    this.rightViewX = trackWidth;
    this.leftTimestamp = displayTransform.xViewToWorld(this.leftViewX);
    this.rightTimestamp = displayTransform.xViewToWorld(this.rightViewX);

    this.displayTransform_ = displayTransform;

    // Y axis.
    this.outerTopViewY = 0;
    this.innerTopViewY = topPadding;
    this.innerBottomViewY = trackHeight - bottomPadding;
    this.outerBottomViewY = trackHeight;

    this.axis_ = axis;
    this.innerHeight_ = this.innerBottomViewY - this.innerTopViewY;
  };

  ChartTransform.prototype = {
    worldXToViewX: function(worldX) {
      return this.displayTransform_.xWorldToView(worldX);
    },

    viewXToWorldX: function(viewX) {
      return this.displayTransform_.xViewToWorld(viewX);
    },

    worldYToViewY: function(worldY) {
      var innerHeightCoefficient = 1 - this.axis_.valueToUnitRange(worldY);
      return innerHeightCoefficient * this.innerHeight_ + this.innerTopViewY;
    }
  };

  return {
    ChartTransform: ChartTransform
  };
});
</script>