[josm-dev] [PATCH] SlippyMap plugin engancements

[Dave Hansen]

With the API down, I'm a little bored.  So, I hacked up the SlippyMap
plugin a bit.  If anything here looks interesting, I'd be happy to break
this out into some slightly more manageable pieces.

Also, has anyone tried adding some caching to the tile fetching?  I'm
using a local squid cache which makes things much nicer, but I'm sure it
would be even better to have something internal to the plugin.

1. Change tileStorage from being a set of arrays of hashmaps (one per
   zoom level) to being a single hash.  We do this by adding a 'level'
   variable to the SlippyMapKey class.  This simplifies the code a good
   amount, and gets rid of a warning when allocating the HashMap array.	
2. Introduce SlippyMapLayer.loadSingleTile().  This not only forces
   the image to get loaded, but also checks the state of the entire
   tileStorage, looking for extra tiles.
3. Add crude timestamping to SlippyMapTile.  Whenever a load of a
   SlippyMapTile is requested, we timestamp it.  This lets us figure
   out which have been least recently used later.
4. Bound the size of the tileStorage.  Every so often, go look at all
   of the tiles.  Sort them by access time.  Drop the image from the
   tile if it isn't one of the 100 most recent ones.  (Make this a
   preference?)
5. Add some sanity checks to SlippyMapKey to make sure we don't add
   negative indexes.  This keeps us from requesting urls like:
   http://a.tile.openstreetmap.org/2/-1/-2.png
6. Introduce a new auto-zoom mechanism.  Right now, it attempts to
   see how many tiles are on the screen.  This is OK, but it can cause
   autozoom changes on just scrolling.  Say you have a screen which
   exactly fits 6x6 tiles.  If you scroll over just a bit, you'll see
   all of those 16 tiles, plus a few pixels of the next row over. 
   You'll all of a sudden be seeing 6x7 tiles, and autozoom will kick
   in.  This new mechanism attempts to detect how much tiles are being
   squished or stretched.  Since it has to load a tile before it can
   actually find out the tile's size, it also has the nice side-effect
   of getting things drawn on the screen earlier.  Should these be
   preferences too?
7. Add debugging to imageUpdate, printing the URL of images that fail to
   load.  Also add a SlippyMapTile.getImageURL() helper to facilitate
   this.
8. Make sure we redraw sooner when changing zoom levels
	

-- Dave
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