As a follow-up to #815, this change makes
ol.tilegrid.createForProjection work in cases where a Proj4
projection does not have units set. For better code readability,
a new variable is used when calculating the resolution.
The projection validity extent is used to generate a sensible
set of default resolutions and a sensible default tile grid.
By making it optional, we can still generate defaults - with
zoom levels that are similar to the default web mercator zoom
levels (based on fitting the world on a single tile, even if the
projection is not available for the whole world).
This change adds a lot of flexibility to working with tile
layers: Sources where the server projection or tile grid do not
matter can now be constructed without specifying a projection or
tile grid.
The tileUrlFunction/imageUrlFunction now also creates updated
URLs when the params of the layer change, so things like
mergeNewParams in ol2 will be possible.
A nice side effect of this whole change is that there is no more
duplicated code between tiled and single image WMS layers.
While I was at it, I also fixed a WMS 1.1.1 axis order issue
and incorrect STYLES params (STYLES=& instead of STYLES&).
Tile ranges are inclusive. When getting the tile range for an extent, the top-right corner of the extent should be considered with a different intersection policy than the bottom-left corner.
When the dom renderer included logic to stretch tiles so that gaps were properly filled for fractional zoom levels, we needed to take this into account when getting a tile coordinate for a given coordinate and resolution. This was never the proper logic for a renderer that wasn't stretching occassional tiles (e.g. the WebGL renderer, the Canvas renderer, or the new DOM renderer).
Previously, the TiledWMS source generated a resolutions array
derived from the world extent in meters, to match the default
Web Mercator resolutions of the map. This wouldn't work for
projections with distance units different than meters. It is
better to commit to a default resolutions array where zoom level
0 is the validity extent of the projection (not the Web Mercator
world extent!) at a 256 pixel tile size.
