MapGuide RFC 132 - Fusion OpenLayers upgrade

This page contains a change request (RFC) for the MapGuide Open Source project. More MapGuide RFCs can be found on the RFCs page.

Status

RFC Template Version	(1.0)
Submission Date	19 Mar 2013
Last Modified	19 Mar 2013
Author	Jackie Ng
RFC Status	draft
Implementation Status	completed
Proposed Milestone	2.6
Assigned PSC guide(s)	(when determined)
Voting History	(vote date)
+1
+0
-0
-1
no vote

Overview

This RFC proposes to upgrade the OpenLayers in Fusion to the latest stable release (2.12)

Motivation

Fusion is using a somewhat old version of OpenLayers.

Upgrading to the latest stable release of OpenLayers (2.12) offers a bunch of useful new features that Fusion can take advantage of:

• Touch input support, allowing for our Fusion templates to be somewhat serviceable on an Android/iOS phone or tablet device, as swipe and pinch zoom functionality can be leveraged automatically for map panning, zooming and navigation.
• Tile Queues, for improved tile loading.
• New CacheRead and CacheWrite controls for limited client-side caching of tile images.
• Client Zoom, allowing for map tile images to be stretched client-side to fit the current view of the map. This one feature alone presents some new scenarios that previously were not possible, such as the ability to have a Map Definition with dynamic and tiled layers acting as a fully dynamic map that can be zoomed to any arbitrary scale without finite scale restrictions (as tiles will be stretched client-side by OpenLayers). Tiles from commerical layers like OpenStreetMap can also be stretched client-side in such a manner.

Proposed Solution

Upgrade Fusion's internal copy of OpenLayers to 2.12

To improve our audit trail of customizations to OpenLayers and to make future OpenLayers upgrades easier, Fusion-specific modifications to OpenLayers are kept under lib/OpenLayers/ext. Whenever a new built OpenLayers.js needs to be checked in, the files and folders under lib/OpenLayers/ext can be copied into a standard OpenLayers distribution (overwriting any existing files) to be built with our fusion.cfg build configuration file.

Currently, we are keeping OpenLayers.Util and our implementation of OpenLayers.Layer.MapGuide under this directory.

The client-zoom feature is controlled by the existing FractionalZoom extension property of the Map widget.

Under client-zoom the following behaviour occurs (under these examples, OSM is interchangeable with any other grid-based tiled layer):

• MapGuide dynamic layers + OSM (fractionalZoom = true): Map is fully dynamic and OSM tiles are stretched accordingly
• MapGuide dynamic layers + OSM (fractionalZoom = false): Scales "snap" to OSM scales and are stretched accordingly when going below the smallest supported OSM scale.

The client-zoom feature has no effect if the map has no tiled layers.

The client-zoom technique does not work in conjunction with Google/Bing layers. See implications

This implementation work has already been completed on the ​ol212 sandbox branch of Fusion. Upon adoption of this RFC, the changes will be merged back into Fusion trunk that's automatically linked by our MapGuide Oem tree.

Implications

The following components in OpenLayers 2.12 are deprecated and we should look at replacing such instances in our core/widget code before another future OpenLayers upgrade:

• OpenLayers.Class.isPrototype
• OpenLayers.Class.create
• OpenLayers.Class.inherit
• OpenLayers.Util.clearArray
• OpenLayers.Util.setOpacity
• OpenLayers.Util.safeStopPropagation
• OpenLayers.Util.getArgs
• OpenLayers.nullHandler
• OpenLayers.loadURL
• OpenLayers.parseXMLString
• OpenLayers.Ajax.* (all methods)
• OpenLayers.Element.hide
• OpenLayers.Element.show
• OpenLayers.Element.getDimensions
• OpenLayers.Tile.prototype.getBoundsFromBaseLayer
• OpenLayers.Control.MouseDefaults
• OpenLayers.Control.MouseToolbar
• OpenLayers.Layer.Grid.prototype.getGridBounds
• OpenLayers.Format.XML.prototype.concatChildValues
• OpenLayers.Layer.WMS.Post
• OpenLayers.Layer.WMS.Untiled
• OpenLayers.Layer.MapServer.Untiled
• OpenLayers.Tile.WFS
• OpenLayers.Feature.WFS
• OpenLayers.Layer.WFS
• OpenLayers.Layer.VirtualEarth
• OpenLayers.Protocol.SQL
• OpenLayers.Protocol.SQL.Gears
• OpenLayers.Layer.Yahoo
• OpenLayers.Layer.GML
• OpenLayers.Geometry.Rectangle
• OpenLayers.Renderer.NG
• OpenLayers.Renderer.SVG2

OpenLayers 2.12 along with the current JxLib presents an issue on Firefox 18+, this is due to the version of MooTools used by JxLib causing "too much recursion" errors under Firefox 18+. As part of this RFC, the MooTools used by JxLib will be upgraded to 1.2.6

The OpenLayers client-zoom feature cannot be used with Google and Bing layers as:

a) These layers aren't Grid-based. Client zoom only works with layers inheriting from OpenLayers.Layer.Grid

b) Client-side stretching of such tiles constitutes content modification of their tiles and violates the terms of use.

If we're viewing a map with Google + Bing + OSM and set the FractionalZoom property of the Map widget to true, switching to a Google or Bing layer will disable client-zoom while that layer is active.

Such limitations should be ideally communicated to the user in the tools/editors department.

Test Plan

Test and verify our changes on our current suite of supported browsers

Funding / Resources

Community