iron-fit-behavior.html

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<link rel="import" href="../polymer/polymer.html">

<script>
  /**
  `Polymer.IronFitBehavior` fits an element in another element using `max-height`
  and `max-width`, and optionally centers it in the window or another element.

  The element will only be sized and/or positioned if it has not already been
  sized and/or positioned by CSS.

  CSS properties               | Action
  -----------------------------|-------------------------------------------
  `position` set               | Element is not centered horizontally or
  vertically `top` or `bottom` set        | Element is not vertically centered
  `left` or `right` set        | Element is not horizontally centered
  `max-height` set             | Element respects `max-height`
  `max-width` set              | Element respects `max-width`

  `Polymer.IronFitBehavior` can position an element into another element using
  `verticalAlign` and `horizontalAlign`. This will override the element's css
  position.

        <div class="container">
          <iron-fit-impl vertical-align="top" horizontal-align="auto">
            Positioned into the container
          </iron-fit-impl>
        </div>

  Use `noOverlap` to position the element around another element without
  overlapping it.

        <div class="container">
          <iron-fit-impl no-overlap vertical-align="auto" horizontal-align="auto">
            Positioned around the container
          </iron-fit-impl>
        </div>

  Use `horizontalOffset, verticalOffset` to offset the element from its
  `positionTarget`; `Polymer.IronFitBehavior` will collapse these in order to keep
  the element within `fitInto` boundaries, while preserving the element's CSS
  margin values.

        <div class="container">
          <iron-fit-impl vertical-align="top" vertical-offset="20">
            With vertical offset
          </iron-fit-impl>
        </div>


  @demo demo/index.html
  @polymerBehavior
  */
  Polymer.IronFitBehavior = {

    properties: {

      /**
       * The element that will receive a `max-height`/`width`. By default it is
       * the same as `this`, but it can be set to a child element. This is useful,
       * for example, for implementing a scrolling region inside the element.
       * @type {!Element}
       */
      sizingTarget: {
        type: Object,
        value: function() {
          return this;
        }
      },

      /**
       * The element to fit `this` into.
       */
      fitInto: {type: Object, value: window},

      /**
       * Will position the element around the positionTarget without overlapping
       * it.
       */
      noOverlap: {type: Boolean},

      /**
       * The element that should be used to position the element. If not set, it
       * will default to the parent node.
       * @type {!Element}
       */
      positionTarget: {type: Element},

      /**
       * The orientation against which to align the element horizontally
       * relative to the `positionTarget`. Possible values are "left", "right",
       * "center", "auto".
       */
      horizontalAlign: {type: String},

      /**
       * The orientation against which to align the element vertically
       * relative to the `positionTarget`. Possible values are "top", "bottom",
       * "middle", "auto".
       */
      verticalAlign: {type: String},

      /**
       * If true, it will use `horizontalAlign` and `verticalAlign` values as
       * preferred alignment and if there's not enough space, it will pick the
       * values which minimize the cropping.
       */
      dynamicAlign: {type: Boolean},

      /**
       * A pixel value that will be added to the position calculated for the
       * given `horizontalAlign`, in the direction of alignment. You can think
       * of it as increasing or decreasing the distance to the side of the
       * screen given by `horizontalAlign`.
       *
       * If `horizontalAlign` is "left" or "center", this offset will increase or
       * decrease the distance to the left side of the screen: a negative offset
       * will move the dropdown to the left; a positive one, to the right.
       *
       * Conversely if `horizontalAlign` is "right", this offset will increase
       * or decrease the distance to the right side of the screen: a negative
       * offset will move the dropdown to the right; a positive one, to the left.
       */
      horizontalOffset: {type: Number, value: 0, notify: true},

      /**
       * A pixel value that will be added to the position calculated for the
       * given `verticalAlign`, in the direction of alignment. You can think
       * of it as increasing or decreasing the distance to the side of the
       * screen given by `verticalAlign`.
       *
       * If `verticalAlign` is "top" or "middle", this offset will increase or
       * decrease the distance to the top side of the screen: a negative offset
       * will move the dropdown upwards; a positive one, downwards.
       *
       * Conversely if `verticalAlign` is "bottom", this offset will increase
       * or decrease the distance to the bottom side of the screen: a negative
       * offset will move the dropdown downwards; a positive one, upwards.
       */
      verticalOffset: {type: Number, value: 0, notify: true},

      /**
       * Set to true to auto-fit on attach.
       */
      autoFitOnAttach: {type: Boolean, value: false},

      /** @type {?Object} */
      _fitInfo: {type: Object}
    },

    get _fitWidth() {
      var fitWidth;
      if (this.fitInto === window) {
        fitWidth = this.fitInto.innerWidth;
      } else {
        fitWidth = this.fitInto.getBoundingClientRect().width;
      }
      return fitWidth;
    },

    get _fitHeight() {
      var fitHeight;
      if (this.fitInto === window) {
        fitHeight = this.fitInto.innerHeight;
      } else {
        fitHeight = this.fitInto.getBoundingClientRect().height;
      }
      return fitHeight;
    },

    get _fitLeft() {
      var fitLeft;
      if (this.fitInto === window) {
        fitLeft = 0;
      } else {
        fitLeft = this.fitInto.getBoundingClientRect().left;
      }
      return fitLeft;
    },

    get _fitTop() {
      var fitTop;
      if (this.fitInto === window) {
        fitTop = 0;
      } else {
        fitTop = this.fitInto.getBoundingClientRect().top;
      }
      return fitTop;
    },

    /**
     * The element that should be used to position the element,
     * if no position target is configured.
     */
    get _defaultPositionTarget() {
      var parent = Polymer.dom(this).parentNode;

      if (parent && parent.nodeType === Node.DOCUMENT_FRAGMENT_NODE) {
        parent = parent.host;
      }

      return parent;
    },

    /**
     * The horizontal align value, accounting for the RTL/LTR text direction.
     */
    get _localeHorizontalAlign() {
      if (this._isRTL) {
        // In RTL, "left" becomes "right".
        if (this.horizontalAlign === 'right') {
          return 'left';
        }
        if (this.horizontalAlign === 'left') {
          return 'right';
        }
      }
      return this.horizontalAlign;
    },

    /**
     * True if the element should be positioned instead of centered.
     * @private
     */
    get __shouldPosition() {
      return (this.horizontalAlign || this.verticalAlign) && this.positionTarget;
    },

    attached: function() {
      // Memoize this to avoid expensive calculations & relayouts.
      // Make sure we do it only once
      if (typeof this._isRTL === 'undefined') {
        this._isRTL = window.getComputedStyle(this).direction == 'rtl';
      }
      this.positionTarget = this.positionTarget || this._defaultPositionTarget;
      if (this.autoFitOnAttach) {
        if (window.getComputedStyle(this).display === 'none') {
          setTimeout(function() {
            this.fit();
          }.bind(this));
        } else {
          // NOTE: shadydom applies distribution asynchronously
          // for performance reasons webcomponents/shadydom#120
          // Flush to get correct layout info.
          window.ShadyDOM && ShadyDOM.flush();
          this.fit();
        }
      }
    },

    detached: function() {
      if (this.__deferredFit) {
        clearTimeout(this.__deferredFit);
        this.__deferredFit = null;
      }
    },

    /**
     * Positions and fits the element into the `fitInto` element.
     */
    fit: function() {
      this.position();
      this.constrain();
      this.center();
    },

    /**
     * Memoize information needed to position and size the target element.
     * @suppress {deprecated}
     */
    _discoverInfo: function() {
      if (this._fitInfo) {
        return;
      }
      var target = window.getComputedStyle(this);
      var sizer = window.getComputedStyle(this.sizingTarget);

      this._fitInfo = {
        inlineStyle: {
          top: this.style.top || '',
          left: this.style.left || '',
          position: this.style.position || ''
        },
        sizerInlineStyle: {
          maxWidth: this.sizingTarget.style.maxWidth || '',
          maxHeight: this.sizingTarget.style.maxHeight || '',
          boxSizing: this.sizingTarget.style.boxSizing || ''
        },
        positionedBy: {
          vertically: target.top !== 'auto' ?
              'top' :
              (target.bottom !== 'auto' ? 'bottom' : null),
          horizontally: target.left !== 'auto' ?
              'left' :
              (target.right !== 'auto' ? 'right' : null)
        },
        sizedBy: {
          height: sizer.maxHeight !== 'none',
          width: sizer.maxWidth !== 'none',
          minWidth: parseInt(sizer.minWidth, 10) || 0,
          minHeight: parseInt(sizer.minHeight, 10) || 0
        },
        margin: {
          top: parseInt(target.marginTop, 10) || 0,
          right: parseInt(target.marginRight, 10) || 0,
          bottom: parseInt(target.marginBottom, 10) || 0,
          left: parseInt(target.marginLeft, 10) || 0
        }
      };
    },

    /**
     * Resets the target element's position and size constraints, and clear
     * the memoized data.
     */
    resetFit: function() {
      var info = this._fitInfo || {};
      for (var property in info.sizerInlineStyle) {
        this.sizingTarget.style[property] = info.sizerInlineStyle[property];
      }
      for (var property in info.inlineStyle) {
        this.style[property] = info.inlineStyle[property];
      }

      this._fitInfo = null;
    },

    /**
     * Equivalent to calling `resetFit()` and `fit()`. Useful to call this after
     * the element or the `fitInto` element has been resized, or if any of the
     * positioning properties (e.g. `horizontalAlign, verticalAlign`) is updated.
     * It preserves the scroll position of the sizingTarget.
     */
    refit: function() {
      var scrollLeft = this.sizingTarget.scrollLeft;
      var scrollTop = this.sizingTarget.scrollTop;
      this.resetFit();
      this.fit();
      this.sizingTarget.scrollLeft = scrollLeft;
      this.sizingTarget.scrollTop = scrollTop;
    },

    /**
     * Positions the element according to `horizontalAlign, verticalAlign`.
     */
    position: function() {
      if (!this.__shouldPosition) {
        // needs to be centered, and it is done after constrain.
        return;
      }
      this._discoverInfo();

      this.style.position = 'fixed';
      // Need border-box for margin/padding.
      this.sizingTarget.style.boxSizing = 'border-box';
      // Set to 0, 0 in order to discover any offset caused by parent stacking
      // contexts.
      this.style.left = '0px';
      this.style.top = '0px';

      var rect = this.getBoundingClientRect();
      var positionRect = this.__getNormalizedRect(this.positionTarget);
      var fitRect = this.__getNormalizedRect(this.fitInto);

      var margin = this._fitInfo.margin;

      // Consider the margin as part of the size for position calculations.
      var size = {
        width: rect.width + margin.left + margin.right,
        height: rect.height + margin.top + margin.bottom
      };

      var position = this.__getPosition(
          this._localeHorizontalAlign,
          this.verticalAlign,
          size,
          rect,
          positionRect,
          fitRect);

      var left = position.left + margin.left;
      var top = position.top + margin.top;

      // We first limit right/bottom within fitInto respecting the margin,
      // then use those values to limit top/left.
      var right = Math.min(fitRect.right - margin.right, left + rect.width);
      var bottom = Math.min(fitRect.bottom - margin.bottom, top + rect.height);

      // Keep left/top within fitInto respecting the margin.
      left = Math.max(
          fitRect.left + margin.left,
          Math.min(left, right - this._fitInfo.sizedBy.minWidth));
      top = Math.max(
          fitRect.top + margin.top,
          Math.min(top, bottom - this._fitInfo.sizedBy.minHeight));

      // Use right/bottom to set maxWidth/maxHeight, and respect
      // minWidth/minHeight.
      this.sizingTarget.style.maxWidth =
          Math.max(right - left, this._fitInfo.sizedBy.minWidth) + 'px';
      this.sizingTarget.style.maxHeight =
          Math.max(bottom - top, this._fitInfo.sizedBy.minHeight) + 'px';

      // Remove the offset caused by any stacking context.
      this.style.left = (left - rect.left) + 'px';
      this.style.top = (top - rect.top) + 'px';
    },

    /**
     * Constrains the size of the element to `fitInto` by setting `max-height`
     * and/or `max-width`.
     */
    constrain: function() {
      if (this.__shouldPosition) {
        return;
      }
      this._discoverInfo();

      var info = this._fitInfo;
      // position at (0px, 0px) if not already positioned, so we can measure the
      // natural size.
      if (!info.positionedBy.vertically) {
        this.style.position = 'fixed';
        this.style.top = '0px';
      }
      if (!info.positionedBy.horizontally) {
        this.style.position = 'fixed';
        this.style.left = '0px';
      }

      // need border-box for margin/padding
      this.sizingTarget.style.boxSizing = 'border-box';
      // constrain the width and height if not already set
      var rect = this.getBoundingClientRect();
      if (!info.sizedBy.height) {
        this.__sizeDimension(
            rect, info.positionedBy.vertically, 'top', 'bottom', 'Height');
      }
      if (!info.sizedBy.width) {
        this.__sizeDimension(
            rect, info.positionedBy.horizontally, 'left', 'right', 'Width');
      }
    },

    /**
     * @protected
     * @deprecated
     */
    _sizeDimension: function(rect, positionedBy, start, end, extent) {
      this.__sizeDimension(rect, positionedBy, start, end, extent);
    },

    /**
     * @private
     */
    __sizeDimension: function(rect, positionedBy, start, end, extent) {
      var info = this._fitInfo;
      var fitRect = this.__getNormalizedRect(this.fitInto);
      var max = extent === 'Width' ? fitRect.width : fitRect.height;
      var flip = (positionedBy === end);
      var offset = flip ? max - rect[end] : rect[start];
      var margin = info.margin[flip ? start : end];
      var offsetExtent = 'offset' + extent;
      var sizingOffset = this[offsetExtent] - this.sizingTarget[offsetExtent];
      this.sizingTarget.style['max' + extent] =
          (max - margin - offset - sizingOffset) + 'px';
    },

    /**
     * Centers horizontally and vertically if not already positioned. This also
     * sets `position:fixed`.
     */
    center: function() {
      if (this.__shouldPosition) {
        return;
      }
      this._discoverInfo();

      var positionedBy = this._fitInfo.positionedBy;
      if (positionedBy.vertically && positionedBy.horizontally) {
        // Already positioned.
        return;
      }
      // Need position:fixed to center
      this.style.position = 'fixed';
      // Take into account the offset caused by parents that create stacking
      // contexts (e.g. with transform: translate3d). Translate to 0,0 and
      // measure the bounding rect.
      if (!positionedBy.vertically) {
        this.style.top = '0px';
      }
      if (!positionedBy.horizontally) {
        this.style.left = '0px';
      }
      // It will take in consideration margins and transforms
      var rect = this.getBoundingClientRect();
      var fitRect = this.__getNormalizedRect(this.fitInto);
      if (!positionedBy.vertically) {
        var top = fitRect.top - rect.top + (fitRect.height - rect.height) / 2;
        this.style.top = top + 'px';
      }
      if (!positionedBy.horizontally) {
        var left = fitRect.left - rect.left + (fitRect.width - rect.width) / 2;
        this.style.left = left + 'px';
      }
    },

    __getNormalizedRect: function(target) {
      if (target === document.documentElement || target === window) {
        return {
          top: 0,
          left: 0,
          width: window.innerWidth,
          height: window.innerHeight,
          right: window.innerWidth,
          bottom: window.innerHeight
        };
      }
      return target.getBoundingClientRect();
    },

    __getOffscreenArea: function(position, size, fitRect) {
      var verticalCrop = Math.min(0, position.top) +
          Math.min(0, fitRect.bottom - (position.top + size.height));
      var horizontalCrop = Math.min(0, position.left) +
          Math.min(0, fitRect.right - (position.left + size.width));
      return Math.abs(verticalCrop) * size.width +
          Math.abs(horizontalCrop) * size.height;
    },


    __getPosition: function(
        hAlign, vAlign, size, sizeNoMargins, positionRect, fitRect) {
      // All the possible configurations.
      // Ordered as top-left, top-right, bottom-left, bottom-right.
      var positions = [
        {
          verticalAlign: 'top',
          horizontalAlign: 'left',
          top: positionRect.top + this.verticalOffset,
          left: positionRect.left + this.horizontalOffset
        },
        {
          verticalAlign: 'top',
          horizontalAlign: 'right',
          top: positionRect.top + this.verticalOffset,
          left: positionRect.right - size.width - this.horizontalOffset
        },
        {
          verticalAlign: 'bottom',
          horizontalAlign: 'left',
          top: positionRect.bottom - size.height - this.verticalOffset,
          left: positionRect.left + this.horizontalOffset
        },
        {
          verticalAlign: 'bottom',
          horizontalAlign: 'right',
          top: positionRect.bottom - size.height - this.verticalOffset,
          left: positionRect.right - size.width - this.horizontalOffset
        }
      ];

      if (this.noOverlap) {
        // Duplicate.
        for (var i = 0, l = positions.length; i < l; i++) {
          var copy = {};
          for (var key in positions[i]) {
            copy[key] = positions[i][key];
          }
          positions.push(copy);
        }
        // Horizontal overlap only.
        positions[0].top = positions[1].top += positionRect.height;
        positions[2].top = positions[3].top -= positionRect.height;
        // Vertical overlap only.
        positions[4].left = positions[6].left += positionRect.width;
        positions[5].left = positions[7].left -= positionRect.width;
      }

      // Consider auto as null for coding convenience.
      vAlign = vAlign === 'auto' ? null : vAlign;
      hAlign = hAlign === 'auto' ? null : hAlign;

      if (!hAlign || hAlign === 'center') {
        positions.push({
          verticalAlign: 'top',
          horizontalAlign: 'center',
          top: positionRect.top + this.verticalOffset +
              (this.noOverlap ? positionRect.height : 0),
          left: positionRect.left - sizeNoMargins.width / 2 +
              positionRect.width / 2 + this.horizontalOffset
        });
        positions.push({
          verticalAlign: 'bottom',
          horizontalAlign: 'center',
          top: positionRect.bottom - size.height - this.verticalOffset -
              (this.noOverlap ? positionRect.height : 0),
          left: positionRect.left - sizeNoMargins.width / 2 +
              positionRect.width / 2 + this.horizontalOffset
        });
      }

      if (!vAlign || vAlign === 'middle') {
        positions.push({
          verticalAlign: 'middle',
          horizontalAlign: 'left',
          top: positionRect.top - sizeNoMargins.height / 2 +
              positionRect.height / 2 + this.verticalOffset,
          left: positionRect.left + this.horizontalOffset +
              (this.noOverlap ? positionRect.width : 0)
        });
        positions.push({
          verticalAlign: 'middle',
          horizontalAlign: 'right',
          top: positionRect.top - sizeNoMargins.height / 2 +
              positionRect.height / 2 + this.verticalOffset,
          left: positionRect.right - size.width - this.horizontalOffset -
              (this.noOverlap ? positionRect.width : 0)
        });
      }

      if (vAlign === 'middle' && hAlign === 'center') {
        positions.push({
          verticalAlign: 'middle',
          horizontalAlign: 'center',
          top: positionRect.top - sizeNoMargins.height / 2 +
              positionRect.height / 2 + this.verticalOffset,
          left: positionRect.left - sizeNoMargins.width / 2 +
              positionRect.width / 2 + this.horizontalOffset
        });
      }

      var position;
      for (var i = 0; i < positions.length; i++) {
        var candidate = positions[i];
        var vAlignOk = candidate.verticalAlign === vAlign;
        var hAlignOk = candidate.horizontalAlign === hAlign;

        // If both vAlign and hAlign are defined, return exact match.
        // For dynamicAlign and noOverlap we'll have more than one candidate, so
        // we'll have to check the offscreenArea to make the best choice.
        if (!this.dynamicAlign && !this.noOverlap && vAlignOk && hAlignOk) {
          position = candidate;
          break;
        }

        // Align is ok if alignment preferences are respected. If no preferences,
        // it is considered ok.
        var alignOk = (!vAlign || vAlignOk) && (!hAlign || hAlignOk);

        // Filter out elements that don't match the alignment (if defined).
        // With dynamicAlign, we need to consider all the positions to find the
        // one that minimizes the cropped area.
        if (!this.dynamicAlign && !alignOk) {
          continue;
        }

        candidate.offscreenArea =
            this.__getOffscreenArea(candidate, size, fitRect);
        // If not cropped and respects the align requirements, keep it.
        // This allows to prefer positions overlapping horizontally over the
        // ones overlapping vertically.
        if (candidate.offscreenArea === 0 && alignOk) {
          position = candidate;
          break;
        }
        position = position || candidate;
        var diff = candidate.offscreenArea - position.offscreenArea;
        // Check which crops less. If it crops equally, check if at least one
        // align setting is ok.
        if (diff < 0 || (diff === 0 && (vAlignOk || hAlignOk))) {
          position = candidate;
        }
      }

      return position;
    }

  };
</script>