In OpenLayers 2.12, the backbuffer for each layer was placed right below
the layer itself. With animated zooming, that was changed so backbuffers
are all placed below the base layer. As it turned out, this is only good
for certain kinds of layers (e.g. street labels), so the default now is
to place the backbuffer right below its layer again. But the
transitionEffect option can now have a new value, 'map-resize', which will
cause the backbuffer to be placed below the base layer.
Since we don't rely on the DOM order for layers, we also cannot rely on it
for backbuffers. This change simply adds a sensible z-index to the
backbuffer container.
When an application zooms the map programmatically right after
initialization, there will be an empty backbuffer. This should be avoided,
because it adds an unnecessary DOM element.
The tile.onLoadEnd handler registers a transitionend listener on the image
of the last loaded tile. But if loading was aborted, there will be no
image. The new logic registers the transitionend event on the last child
of the layer div, which is not necessarily the tile we're handling loadend
for. When the backbuffer is empty (i.e. no tile was loaded at the time the
backbuffer was created), it will be removed immediately.
This change introduces a new 'replace' mode for tile transitions: when the
resolution does not change, which happens when mergeNewParams is called,
the tile will be marked with the .olTileReplace class. If this class sets
the tile's imgDiv display to 'none', the backbuffer for the tile will
immediately be removed when the tile is loaded.
We now reuse tile images by maintaining a cache of image elements with a
simplified LRU expiry policy (by order, not by timestamp). The tile queue
is bypassed for images that are available in the cache, so they can be
rendered immediately. And the tile queue itself loads more than just one
image at a time now (2 per layer url).
Using the Timeline tab of the Chrome Developer Tools, no significant
difference of Paint events can be observed when requestAnimationFrame is
used. So I agree with @elemoine that there is no need to introduce
asynchronous behavior here.
This is because the threshold used for deciding when a column or row is shifted is too far to the bottom right. A tiny fix, but effective. A new test makes sure that we don't shift columns more than necessary when the layer is dragged.
If a layer is configured with serverResolutions, then getServerZoom should return the zoom level as index of the current resolution in the serverResolutions array.
layer.maxExtent is always set as soon as the layer is added to a map. Instead, making behavior consistent with tiled layers: don't display outside maxExtent except when displayOutsideMaxExtent is set to true or the layer's extent equals the world bounds for maps with a baseLayer that has wrapDateLine set to true.
For this to be useful (i.e. so listeners can see/modify the tile url), a change in Tile.Image is required so we do not fire the loadstart event before we have the url to load.
Since draw is the only tile operation that we defer, the tile queue can be an array of tiles and queue handling can be simplified. We now use the beforedraw event to defer drawing, and remove all occurrences of a tile from the tile queue when we draw it.
Instead of layers that want to defer tile drawing having to override the tile's draw method, layers can now abort drawing by returning false from a beforedraw listener, and later call draw(true) to draw the tile directly, without clearing it first.
