Layer/FixedZoomLevels

FixedZoomLevels Layer

Taken directly from class-definition header in OpenLayers/Layer/FixedZoomLevels.js 

/** 
 *   Some Layers will already have established zoom levels (like google 
 *    or ve). Instead of trying to determine them and populate a resolutions[]
 *    Array with those values, we will hijack the resolution functionality
 *    here.
 * 
 *   When you subclass FixedZoomLevels: 
 * 
 *   The initResolutions() call gets nullified, meaning no resolutions[] array 
 *    is set up. Which would be a big problem getResolution() in Layer, since 
 *    it merely takes map.zoom and indexes into resolutions[]... but....
 * 
 *   The getResolution() call is also overridden. Instead of using the 
 *    resolutions[] array, we simply calculate the current resolution based
 *    on the current extent and the current map size. But how will we be able
 *    to calculate the current extent without knowing the resolution...?
 *  
 *   The getExtent() function is also overridden. Instead of calculating extent
 *    based on the center point and the current resolution, we instead 
 *    calculate the extent by getting the lonlats at the top-left and 
 *    bottom-right by using the getLonLatFromViewPortPx() translation function,
 *    taken from the pixel locations (0,0) and the size of the map. But how 
 *    will we be able to do lonlat-px translation without resolution....?
 * 
 *   The getZoomForResolution() method is overridden. Instead of indexing into
 *    the resolutions[] array, we call OpenLayers.Layer.getExent(), passing in
 *    the desired resolution. With this extent, we then call getZoomForExtent() 
 * 
 * 
 *   Whenever you implement a layer using OpenLayers.Layer.FixedZoomLevels, 
 *    it is your responsibility to provide the following three functions:
 * 
 *   - getLonLatFromViewPortPx()
 *   - getViewPortPxFromLonLat()
 *   - getZoomForExtent()
 * 
 *  ...those three functions should generally be provided by any reasonable 
 *  API that you might be working from.
 * 
 * @class
 */