/
Layer.js
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Layer.js
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/* Copyright (c) 2006-2012 by OpenLayers Contributors (see authors.txt for
* full list of contributors). Published under the Clear BSD license.
* See http://svn.openlayers.org/trunk/openlayers/license.txt for the
* full text of the license. */
/**
* @requires OpenLayers/BaseTypes/Class.js
* @requires OpenLayers/Map.js
* @requires OpenLayers/Projection.js
*/
/**
* Class: OpenLayers.Layer
*/
OpenLayers.Layer = OpenLayers.Class({
/**
* APIProperty: id
* {String}
*/
id: null,
/**
* APIProperty: name
* {String}
*/
name: null,
/**
* APIProperty: div
* {DOMElement}
*/
div: null,
/**
* Property: opacity
* {Float} The layer's opacity. Float number between 0.0 and 1.0. Default
* is 1.
*/
opacity: 1,
/**
* APIProperty: alwaysInRange
* {Boolean} If a layer's display should not be scale-based, this should
* be set to true. This will cause the layer, as an overlay, to always
* be 'active', by always returning true from the calculateInRange()
* function.
*
* If not explicitly specified for a layer, its value will be
* determined on startup in initResolutions() based on whether or not
* any scale-specific properties have been set as options on the
* layer. If no scale-specific options have been set on the layer, we
* assume that it should always be in range.
*
* See #987 for more info.
*/
alwaysInRange: null,
/**
* Register a listener for a particular event with the following syntax:
* (code)
* layer.events.register(type, obj, listener);
* (end)
*
* Listeners will be called with a reference to an event object. The
* properties of this event depends on exactly what happened.
*
* All event objects have at least the following properties:
* object - {Object} A reference to layer.events.object.
* element - {DOMElement} A reference to layer.events.element.
*
* Supported map event types:
* loadstart - Triggered when layer loading starts.
* loadend - Triggered when layer loading ends.
* loadcancel - Triggered when layer loading is canceled.
* visibilitychanged - Triggered when layer visibility is changed.
* move - Triggered when layer moves (triggered with every mousemove
* during a drag).
* moveend - Triggered when layer is done moving, object passed as
* argument has a zoomChanged boolean property which tells that the
* zoom has changed.
* added - Triggered after the layer is added to a map. Listeners will
* receive an object with a *map* property referencing the map and a
* *layer* property referencing the layer.
* removed - Triggered after the layer is removed from the map. Listeners
* will receive an object with a *map* property referencing the map and
* a *layer* property referencing the layer.
*/
/**
* Constant: RESOLUTION_PROPERTIES
* {Array} The properties that are used for calculating resolutions
* information.
*/
RESOLUTION_PROPERTIES: [
'scales', 'resolutions',
'maxScale', 'minScale',
'maxResolution', 'minResolution',
'numZoomLevels', 'maxZoomLevel'
],
/**
* APIProperty: events
* {<OpenLayers.Events>}
*/
events: null,
/**
* APIProperty: map
* {<OpenLayers.Map>} This variable is set when the layer is added to
* the map, via the accessor function setMap().
*/
map: null,
/**
* APIProperty: isBaseLayer
* {Boolean} Whether or not the layer is a base layer. This should be set
* individually by all subclasses. Default is false
*/
isBaseLayer: false,
/**
* Property: alpha
* {Boolean} The layer's images have an alpha channel. Default is false.
*/
alpha: false,
/**
* APIProperty: displayInLayerSwitcher
* {Boolean} Display the layer's name in the layer switcher. Default is
* true.
*/
displayInLayerSwitcher: true,
/**
* APIProperty: visibility
* {Boolean} The layer should be displayed in the map. Default is true.
*/
visibility: true,
/**
* APIProperty: attribution
* {String} Attribution string, displayed when an
* <OpenLayers.Control.Attribution> has been added to the map.
*/
attribution: null,
/**
* Property: inRange
* {Boolean} The current map resolution is within the layer's min/max
* range. This is set in <OpenLayers.Map.setCenter> whenever the zoom
* changes.
*/
inRange: false,
/**
* Propery: imageSize
* {<OpenLayers.Size>} For layers with a gutter, the image is larger than
* the tile by twice the gutter in each dimension.
*/
imageSize: null,
/**
* Property: imageOffset
* {<OpenLayers.Pixel>} For layers with a gutter, the image offset
* represents displacement due to the gutter.
*/
imageOffset: null,
// OPTIONS
/**
* Property: options
* {Object} An optional object whose properties will be set on the layer.
* Any of the layer properties can be set as a property of the options
* object and sent to the constructor when the layer is created.
*/
options: null,
/**
* APIProperty: eventListeners
* {Object} If set as an option at construction, the eventListeners
* object will be registered with <OpenLayers.Events.on>. Object
* structure must be a listeners object as shown in the example for
* the events.on method.
*/
eventListeners: null,
/**
* APIProperty: gutter
* {Integer} Determines the width (in pixels) of the gutter around image
* tiles to ignore. By setting this property to a non-zero value,
* images will be requested that are wider and taller than the tile
* size by a value of 2 x gutter. This allows artifacts of rendering
* at tile edges to be ignored. Set a gutter value that is equal to
* half the size of the widest symbol that needs to be displayed.
* Defaults to zero. Non-tiled layers always have zero gutter.
*/
gutter: 0,
/**
* APIProperty: projection
* {<OpenLayers.Projection>} or {<String>} Set in the layer options to
* override the default projection string this layer - also set maxExtent,
* maxResolution, and units if appropriate. Can be either a string or
* an <OpenLayers.Projection> object when created -- will be converted
* to an object when setMap is called if a string is passed.
*/
projection: null,
/**
* APIProperty: units
* {String} The layer map units. Defaults to 'degrees'. Possible values
* are 'degrees' (or 'dd'), 'm', 'ft', 'km', 'mi', 'inches'.
*/
units: null,
/**
* APIProperty: scales
* {Array} An array of map scales in descending order. The values in the
* array correspond to the map scale denominator. Note that these
* values only make sense if the display (monitor) resolution of the
* client is correctly guessed by whomever is configuring the
* application. In addition, the units property must also be set.
* Use <resolutions> instead wherever possible.
*/
scales: null,
/**
* APIProperty: resolutions
* {Array} A list of map resolutions (map units per pixel) in descending
* order. If this is not set in the layer constructor, it will be set
* based on other resolution related properties (maxExtent,
* maxResolution, maxScale, etc.).
*/
resolutions: null,
/**
* APIProperty: maxExtent
* {<OpenLayers.Bounds>} The center of these bounds will not stray outside
* of the viewport extent during panning. In addition, if
* <displayOutsideMaxExtent> is set to false, data will not be
* requested that falls completely outside of these bounds.
*/
maxExtent: null,
/**
* APIProperty: minExtent
* {<OpenLayers.Bounds>}
*/
minExtent: null,
/**
* APIProperty: maxResolution
* {Float} Default max is 360 deg / 256 px, which corresponds to
* zoom level 0 on gmaps. Specify a different value in the layer
* options if you are not using a geographic projection and
* displaying the whole world.
*/
maxResolution: null,
/**
* APIProperty: minResolution
* {Float}
*/
minResolution: null,
/**
* Property: resolution
* {Float} Current resolution that the layer is drawn in. This is
* used to determine whether the zoom has changed when calling
* <moveTo> from <redraw>. Subclasses may set this.resolution to
* null prior to calling redraw to force passing zoomChanged
* true to moveTo.
*/
resolution: null,
/**
* APIProperty: numZoomLevels
* {Integer}
*/
numZoomLevels: null,
/**
* APIProperty: minScale
* {Float}
*/
minScale: null,
/**
* APIProperty: maxScale
* {Float}
*/
maxScale: null,
/**
* APIProperty: displayOutsideMaxExtent
* {Boolean} Request map tiles that are completely outside of the max
* extent for this layer. Defaults to false.
*/
displayOutsideMaxExtent: false,
/**
* APIProperty: wrapDateLine
* {Boolean} Wraps the world at the international dateline, so the map can
* be panned infinitely in longitudinal direction. Only use this on the
* base layer, and only if the layer's maxExtent equals the world bounds.
* #487 for more info.
*/
wrapDateLine: false,
/**
* APIProperty: transitionEffect
* {String} The transition effect to use when the map is panned or
* zoomed.
*
* There are currently two supported values:
* - *null* No transition effect (the default).
* - *resize* Existing tiles are resized on zoom to provide a visual
* effect of the zoom having taken place immediately. As the
* new tiles become available, they are drawn over top of the
* resized tiles.
*/
transitionEffect: null,
/**
* Property: metadata
* {Object} This object can be used to store additional information on a
* layer object.
*/
metadata: {},
/**
* Constructor: OpenLayers.Layer
*
* Parameters:
* name - {String} The layer name
* options - {Object} Hashtable of extra options to tag onto the layer
*/
initialize: function(name, options) {
this.addOptions(options);
this.name = name;
if (this.id == null) {
this.id = OpenLayers.Util.createUniqueID(this.CLASS_NAME + "_");
this.div = OpenLayers.Util.createDiv(this.id);
this.div.style.width = "100%";
this.div.style.height = "100%";
this.div.dir = "ltr";
this.events = new OpenLayers.Events(this, this.div);
if(this.eventListeners instanceof Object) {
this.events.on(this.eventListeners);
}
}
if (this.wrapDateLine) {
this.displayOutsideMaxExtent = true;
}
},
/**
* Method: destroy
* Destroy is a destructor: this is to alleviate cyclic references which
* the Javascript garbage cleaner can not take care of on its own.
*
* Parameters:
* setNewBaseLayer - {Boolean} Set a new base layer when this layer has
* been destroyed. Default is true.
*/
destroy: function(setNewBaseLayer) {
if (setNewBaseLayer == null) {
setNewBaseLayer = true;
}
if (this.map != null) {
this.map.removeLayer(this, setNewBaseLayer);
}
this.projection = null;
this.map = null;
this.name = null;
this.div = null;
this.options = null;
if (this.events) {
if(this.eventListeners) {
this.events.un(this.eventListeners);
}
this.events.destroy();
}
this.eventListeners = null;
this.events = null;
},
/**
* Method: clone
*
* Parameters:
* obj - {<OpenLayers.Layer>} The layer to be cloned
*
* Returns:
* {<OpenLayers.Layer>} An exact clone of this <OpenLayers.Layer>
*/
clone: function (obj) {
if (obj == null) {
obj = new OpenLayers.Layer(this.name, this.getOptions());
}
// catch any randomly tagged-on properties
OpenLayers.Util.applyDefaults(obj, this);
// a cloned layer should never have its map property set
// because it has not been added to a map yet.
obj.map = null;
return obj;
},
/**
* Method: getOptions
* Extracts an object from the layer with the properties that were set as
* options, but updates them with the values currently set on the
* instance.
*
* Returns:
* {Object} the <options> of the layer, representing the current state.
*/
getOptions: function() {
var options = {};
for(var o in this.options) {
options[o] = this[o];
}
return options;
},
/**
* APIMethod: setName
* Sets the new layer name for this layer. Can trigger a changelayer event
* on the map.
*
* Parameters:
* newName - {String} The new name.
*/
setName: function(newName) {
if (newName != this.name) {
this.name = newName;
if (this.map != null) {
this.map.events.triggerEvent("changelayer", {
layer: this,
property: "name"
});
}
}
},
/**
* APIMethod: addOptions
*
* Parameters:
* newOptions - {Object}
* reinitialize - {Boolean} If set to true, and if resolution options of the
* current baseLayer were changed, the map will be recentered to make
* sure that it is displayed with a valid resolution, and a
* changebaselayer event will be triggered.
*/
addOptions: function (newOptions, reinitialize) {
if (this.options == null) {
this.options = {};
}
// allow array for extents
if (newOptions) {
if (newOptions.maxExtent && !(newOptions.maxExtent instanceof OpenLayers.Bounds)) {
newOptions.maxExtent = new OpenLayers.Bounds(newOptions.maxExtent);
}
if (newOptions.minExtent && !(newOptions.minExtent instanceof OpenLayers.Bounds)) {
newOptions.minExtent = new OpenLayers.Bounds(newOptions.minExtent);
}
}
// update our copy for clone
OpenLayers.Util.extend(this.options, newOptions);
// add new options to this
OpenLayers.Util.extend(this, newOptions);
// make sure this.projection references a projection object
if(typeof this.projection == "string") {
this.projection = new OpenLayers.Projection(this.projection);
}
// get the units from the projection, if we have a projection
// and it it has units
if(this.projection && this.projection.getUnits()) {
this.units = this.projection.getUnits();
}
// re-initialize resolutions if necessary, i.e. if any of the
// properties of the "properties" array defined below is set
// in the new options
if(this.map) {
// store current resolution so we can try to restore it later
var resolution = this.map.getResolution();
var properties = this.RESOLUTION_PROPERTIES.concat(
["projection", "units", "minExtent", "maxExtent"]
);
for(var o in newOptions) {
if(newOptions.hasOwnProperty(o) &&
OpenLayers.Util.indexOf(properties, o) >= 0) {
this.initResolutions();
if (reinitialize && this.map.baseLayer === this) {
// update map position, and restore previous resolution
this.map.setCenter(this.map.getCenter(),
this.map.getZoomForResolution(resolution),
false, true
);
// trigger a changebaselayer event to make sure that
// all controls (especially
// OpenLayers.Control.PanZoomBar) get notified of the
// new options
this.map.events.triggerEvent("changebaselayer", {
layer: this
});
}
break;
}
}
}
},
/**
* APIMethod: onMapResize
* This function can be implemented by subclasses
*/
onMapResize: function() {
//this function can be implemented by subclasses
},
/**
* APIMethod: redraw
* Redraws the layer. Returns true if the layer was redrawn, false if not.
*
* Returns:
* {Boolean} The layer was redrawn.
*/
redraw: function() {
var redrawn = false;
if (this.map) {
// min/max Range may have changed
this.inRange = this.calculateInRange();
// map's center might not yet be set
var extent = this.getExtent();
if (extent && this.inRange && this.visibility) {
zoomChanged = this.resolution == null ||
this.resolution !== this.map.getResolution();
this.moveTo(extent, zoomChanged, false);
this.events.triggerEvent("moveend",
{"zoomChanged": zoomChanged});
redrawn = true;
}
}
return redrawn;
},
/**
* Method: moveTo
*
* Parameters:
* bounds - {<OpenLayers.Bounds>}
* zoomChanged - {Boolean} Tells when zoom has changed, as layers have to
* do some init work in that case.
* dragging - {Boolean}
*/
moveTo:function(bounds, zoomChanged, dragging) {
var display = this.visibility;
if (!this.isBaseLayer) {
display = display && this.inRange;
}
this.display(display);
this.resolution = this.map.getResolution();
},
/**
* Method: moveByPx
* Move the layer based on pixel vector. To be implemented by subclasses.
*
* Parameters:
* dx - {Number} The x coord of the displacement vector.
* dy - {Number} The y coord of the displacement vector.
*/
moveByPx: function(dx, dy) {
},
/**
* Method: setMap
* Set the map property for the layer. This is done through an accessor
* so that subclasses can override this and take special action once
* they have their map variable set.
*
* Here we take care to bring over any of the necessary default
* properties from the map.
*
* Parameters:
* map - {<OpenLayers.Map>}
*/
setMap: function(map) {
if (this.map == null) {
this.map = map;
// grab some essential layer data from the map if it hasn't already
// been set
this.maxExtent = this.maxExtent || this.map.maxExtent;
this.minExtent = this.minExtent || this.map.minExtent;
this.projection = this.projection || this.map.projection;
if (typeof this.projection == "string") {
this.projection = new OpenLayers.Projection(this.projection);
}
// Check the projection to see if we can get units -- if not, refer
// to properties.
this.units = this.projection.getUnits() ||
this.units || this.map.units;
this.initResolutions();
if (!this.isBaseLayer) {
this.inRange = this.calculateInRange();
var show = ((this.visibility) && (this.inRange));
this.div.style.display = show ? "" : "none";
}
// deal with gutters
this.setTileSize();
this.resolution = null;
}
},
/**
* Method: afterAdd
* Called at the end of the map.addLayer sequence. At this point, the map
* will have a base layer. To be overridden by subclasses.
*/
afterAdd: function() {
},
/**
* APIMethod: removeMap
* Just as setMap() allows each layer the possibility to take a
* personalized action on being added to the map, removeMap() allows
* each layer to take a personalized action on being removed from it.
* For now, this will be mostly unused, except for the EventPane layer,
* which needs this hook so that it can remove the special invisible
* pane.
*
* Parameters:
* map - {<OpenLayers.Map>}
*/
removeMap: function(map) {
//to be overridden by subclasses
},
/**
* APIMethod: getImageSize
*
* Parameters:
* bounds - {<OpenLayers.Bounds>} optional tile bounds, can be used
* by subclasses that have to deal with different tile sizes at the
* layer extent edges (e.g. Zoomify)
*
* Returns:
* {<OpenLayers.Size>} The size that the image should be, taking into
* account gutters.
*/
getImageSize: function(bounds) {
return (this.imageSize || this.tileSize);
},
/**
* APIMethod: setTileSize
* Set the tile size based on the map size. This also sets layer.imageSize
* and layer.imageOffset for use by Tile.Image.
*
* Parameters:
* size - {<OpenLayers.Size>}
*/
setTileSize: function(size) {
var tileSize = (size) ? size :
((this.tileSize) ? this.tileSize :
this.map.getTileSize());
this.tileSize = tileSize;
if(this.gutter) {
// layers with gutters need non-null tile sizes
//if(tileSize == null) {
// OpenLayers.console.error("Error in layer.setMap() for " +
// this.name + ": layers with " +
// "gutters need non-null tile sizes");
//}
this.imageOffset = new OpenLayers.Pixel(-this.gutter,
-this.gutter);
this.imageSize = new OpenLayers.Size(tileSize.w + (2*this.gutter),
tileSize.h + (2*this.gutter));
}
},
/**
* APIMethod: getVisibility
*
* Returns:
* {Boolean} The layer should be displayed (if in range).
*/
getVisibility: function() {
return this.visibility;
},
/**
* APIMethod: setVisibility
* Set the visibility flag for the layer and hide/show & redraw
* accordingly. Fire event unless otherwise specified
*
* Note that visibility is no longer simply whether or not the layer's
* style.display is set to "block". Now we store a 'visibility' state
* property on the layer class, this allows us to remember whether or
* not we *desire* for a layer to be visible. In the case where the
* map's resolution is out of the layer's range, this desire may be
* subverted.
*
* Parameters:
* visibility - {Boolean} Whether or not to display the layer (if in range)
*/
setVisibility: function(visibility) {
if (visibility != this.visibility) {
this.visibility = visibility;
this.display(visibility);
this.redraw();
if (this.map != null) {
this.map.events.triggerEvent("changelayer", {
layer: this,
property: "visibility"
});
}
this.events.triggerEvent("visibilitychanged");
}
},
/**
* APIMethod: display
* Hide or show the Layer. This is designed to be used internally, and
* is not generally the way to enable or disable the layer. For that,
* use the setVisibility function instead..
*
* Parameters:
* display - {Boolean}
*/
display: function(display) {
if (display != (this.div.style.display != "none")) {
this.div.style.display = (display && this.calculateInRange()) ? "block" : "none";
}
},
/**
* APIMethod: calculateInRange
*
* Returns:
* {Boolean} The layer is displayable at the current map's current
* resolution. Note that if 'alwaysInRange' is true for the layer,
* this function will always return true.
*/
calculateInRange: function() {
var inRange = false;
if (this.alwaysInRange) {
inRange = true;
} else {
if (this.map) {
var resolution = this.map.getResolution();
inRange = ( (resolution >= this.minResolution) &&
(resolution <= this.maxResolution) );
}
}
return inRange;
},
/**
* APIMethod: setIsBaseLayer
*
* Parameters:
* isBaseLayer - {Boolean}
*/
setIsBaseLayer: function(isBaseLayer) {
if (isBaseLayer != this.isBaseLayer) {
this.isBaseLayer = isBaseLayer;
if (this.map != null) {
this.map.events.triggerEvent("changebaselayer", {
layer: this
});
}
}
},
/********************************************************/
/* */
/* Baselayer Functions */
/* */
/********************************************************/
/**
* Method: initResolutions
* This method's responsibility is to set up the 'resolutions' array
* for the layer -- this array is what the layer will use to interface
* between the zoom levels of the map and the resolution display
* of the layer.
*
* The user has several options that determine how the array is set up.
*
* For a detailed explanation, see the following wiki from the
* openlayers.org homepage:
* http://trac.openlayers.org/wiki/SettingZoomLevels
*/
initResolutions: function() {
// ok we want resolutions, here's our strategy:
//
// 1. if resolutions are defined in the layer config, use them
// 2. else, if scales are defined in the layer config then derive
// resolutions from these scales
// 3. else, attempt to calculate resolutions from maxResolution,
// minResolution, numZoomLevels, maxZoomLevel set in the
// layer config
// 4. if we still don't have resolutions, and if resolutions
// are defined in the same, use them
// 5. else, if scales are defined in the map then derive
// resolutions from these scales
// 6. else, attempt to calculate resolutions from maxResolution,
// minResolution, numZoomLevels, maxZoomLevel set in the
// map
// 7. hope for the best!
var i, len, p;
var props = {}, alwaysInRange = true;
// get resolution data from layer config
// (we also set alwaysInRange in the layer as appropriate)
for(i=0, len=this.RESOLUTION_PROPERTIES.length; i<len; i++) {
p = this.RESOLUTION_PROPERTIES[i];
props[p] = this.options[p];
if(alwaysInRange && this.options[p]) {
alwaysInRange = false;
}
}
if(this.alwaysInRange == null) {
this.alwaysInRange = alwaysInRange;
}
// if we don't have resolutions then attempt to derive them from scales
if(props.resolutions == null) {
props.resolutions = this.resolutionsFromScales(props.scales);
}
// if we still don't have resolutions then attempt to calculate them
if(props.resolutions == null) {
props.resolutions = this.calculateResolutions(props);
}
// if we couldn't calculate resolutions then we look at we have
// in the map
if(props.resolutions == null) {
for(i=0, len=this.RESOLUTION_PROPERTIES.length; i<len; i++) {
p = this.RESOLUTION_PROPERTIES[i];
props[p] = this.options[p] != null ?
this.options[p] : this.map[p];
}
if(props.resolutions == null) {
props.resolutions = this.resolutionsFromScales(props.scales);
}
if(props.resolutions == null) {
props.resolutions = this.calculateResolutions(props);
}
}
// ok, we new need to set properties in the instance
// get maxResolution from the config if it's defined there
var maxResolution;
if(this.options.maxResolution &&
this.options.maxResolution !== "auto") {
maxResolution = this.options.maxResolution;
}
if(this.options.minScale) {
maxResolution = OpenLayers.Util.getResolutionFromScale(
this.options.minScale, this.units);
}
// get minResolution from the config if it's defined there
var minResolution;
if(this.options.minResolution &&
this.options.minResolution !== "auto") {
minResolution = this.options.minResolution;
}
if(this.options.maxScale) {
minResolution = OpenLayers.Util.getResolutionFromScale(
this.options.maxScale, this.units);
}
if(props.resolutions) {
//sort resolutions array descendingly
props.resolutions.sort(function(a, b) {
return (b - a);
});
// if we still don't have a maxResolution get it from the
// resolutions array
if(!maxResolution) {
maxResolution = props.resolutions[0];
}
// if we still don't have a minResolution get it from the
// resolutions array
if(!minResolution) {
var lastIdx = props.resolutions.length - 1;
minResolution = props.resolutions[lastIdx];
}
}
this.resolutions = props.resolutions;
if(this.resolutions) {
len = this.resolutions.length;
this.scales = new Array(len);
for(i=0; i<len; i++) {
this.scales[i] = OpenLayers.Util.getScaleFromResolution(
this.resolutions[i], this.units);
}
this.numZoomLevels = len;
}
this.minResolution = minResolution;
if(minResolution) {
this.maxScale = OpenLayers.Util.getScaleFromResolution(
minResolution, this.units);
}
this.maxResolution = maxResolution;
if(maxResolution) {
this.minScale = OpenLayers.Util.getScaleFromResolution(
maxResolution, this.units);
}
},
/**
* Method: resolutionsFromScales
* Derive resolutions from scales.
*
* Parameters:
* scales - {Array(Number)} Scales
*
* Returns
* {Array(Number)} Resolutions
*/
resolutionsFromScales: function(scales) {
if(scales == null) {
return;
}
var resolutions, i, len;
len = scales.length;
resolutions = new Array(len);
for(i=0; i<len; i++) {
resolutions[i] = OpenLayers.Util.getResolutionFromScale(
scales[i], this.units);
}
return resolutions;
},
/**
* Method: calculateResolutions
* Calculate resolutions based on the provided properties.
*
* Parameters:
* props - {Object} Properties
*
* Returns:
* {Array({Number})} Array of resolutions.
*/
calculateResolutions: function(props) {
var viewSize, wRes, hRes;
// determine maxResolution
var maxResolution = props.maxResolution;