Now vector layers can have a style. ol.Style instances have an
apply method to get the symbolizer literals for a feature. If the
layer does not have a style defined, there is also a static
applyDefaultStyle function on ol.Style to get the default
symbolizer literals for a feature. The vector layer also got a
groupFeaturesBySymbolizerLiteral method, which returns an array
with features grouped by symbolizer, as needed by the canvas
renderer.
If we have a gridded vector source, the grid should have something to do with the source data (e.g. the vector data is available in a regular grid). The vector layer renderer's internal grid is for rendering canvas tiles and doesn't have anything to do with the source.
We should discuss whether post render functions must be run after each render frame or not. If these can be run after multiple render frames, it would make sense to increase the timeout. As it is, it looks like post render functions are run for every render. Hard to see what the benefit is in this case.
* Tiles are now cut out of the sketch renderer in a separate
pass. This ensures that point features at tile borders appear
at both sides of the border. However, if such features get
added in a later tileRange rendering pass, tiles from a
previous rendering pass will still not have that feature.
* The tile canvas is only created once, and cloneNode(false) is
used to get a canvas for a new tile.
It looks like this approach will work well for panning (as anticipated). For animated zooming, it is not going to work as is. It looks like the canvas tile generation is too much for this type of animation loop. Though there are clearly still areas for optimization:
* Don't create new tiles while animating between zoom levels. Using existing tiles only while animating should bring a significant performance gain.
* Simple spatial index for tiles - each tile coord in the matrix could have a feature lookup object (keyed by id). This needs to account for rendered dimension (as witnessed by the point being cut by a tile). Given that the current example uses only three features, adding the spatial index should only be a minor improvement.
* Reuse a fixed set of canvas tiles that are generated at construction (and increased/decreased with view size changes).
* If a fixed set of tiles is not used, at least new ones could be cloned from existing ones (minor).
* Do some profiling to look for more ideas.
In addition, world-wrapping needs addressed. I don't think this renderer is the right (or at least the only) place to address this. And the cache of tiles needs to be managed for real. But hey, at least we've got a working tiled vector renderer now.
I think it's complicating things at this point to deal with this. Unfortunately, it's not proper dateline wrapping as is (only arbitrary tile range extent wrapping).
What we want in the end is vector tiles repeated just as raster
tiles. This change only avoids repeated tiles with the same
content being rendered and stored in the cache.
This needs more work still - see inline TODOs. It also has a
major bug - rendered vector features do not scale and do not
change their offset during panning. So only the initial view is
correct.
There is a ton of room for optimization here. The vector layer renderer should only render dirty areas and could maintain a cache of rendered canvas tiles. The vector source could have a simple spatial index for features (by tile coord). Need to also discuss how to work with this animation framework (to avoid the excess work while waiting for tiles to load on every other layer).
