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.
The ol3 version of the library is more advanced and complete. It can also
parse into flat array. It can handle unsigned integers, signed integers
and floats.
With two nested controls (DragFeature, SelectFeature), which - among
others - activated two OpenLayers.Handler.Feature instances, the
ModifyFeature control was fragile and hard to debug.
The issue that @iwillig, @bartvde and myself tried to track down was
that the two Feature handlers interfered with each other, making it hard
to select features on mobile devices, and causing points to jump during
dragging because of not updated last pixel positions.
With this refactoring, there are no more nested controls. All that's left
is a Drag handler. All tests pass. I had to remove one test that checked
for dragging of an unselected point while another was selected, because
now (and partially even before this change, thanks to the ugly drag
handler hack that is now removed) dragging a point will also select it,
saving the user an extra click.
Quick explanation:
Let targetCenterPx be described by PX and PY. Let oldRes and newRes be R0 and R1 respectively. Let centerPx (center after zoom) be described by CX and CY. And assume there is some anchored pixel point out there that represents the same map location before and after zoom. Let this be the origin OX and OY.
We want to recenter the map on the provided box. This means the map distance between the origin and box center at R0 is the same as the map distance between the origin and the map center at R1.
That is,
R0 * (OX - PX) = R1 * (OX - CX), and
R1 * (OY - PY) = R1 * (OY - CY)
Or, solving for OX and OY:
OX = (R0 * PX - R1 * CX) / (R0 - R1), and
OY = (R0 * PY - R1 * CY) / (R0 - R1)
When the TileManager adds an image to its cache, it might be a backbuffer
image. Backbuffer images have an id with a '_bb' postfix. Regular images
do not have an id at all. In OpenLayers.Layer.Grid, in
addTileMonitoringHooks, a loadend listener is created for each tile. This
listener checks for tie image id, and will remove it from its parent node.
This will cause images to be removed from the layerDiv if the image comes
from the TileManager's tileCache and was on a backbuffer by the time it was
added to the cache.
Simply removing the image's id before assigning it to a tile resolves the
issue.
