Currently, the dirty flag is never reset (to false). This is a bug. Because renderFrame is called very often (every layer render gets called when every other layer needs to re-render), it is criticial to know when we can bail out early. The dirty flag is currently the way that the vector layer renderer knows that it needs to do more work. On an empty cache, the renderFrame method of the vector layer renderer is called ~30 times for a single zoom in the vector layer example (due to tiles loading on other layers). Without this change, we miss the fast path out and clear/re-render the canvas all 30 times. With this change, we are only clear the canvas and redraw 6 times in a typical zoom animation.
The reason for this change is that symbolSizes and maxSymbolSize
on the instance will be wrong as soon as the resolution changes
and cached tiles are used. It turned out that the approach used
now has several advantages: smaller symbolSizes objects, no need
to merge symbolSizes objects, and cache management for free (no
risk of memory leaks). Note that the symbolSizes and
maxSymbolSize for each tile are not strictly tile specific -
they represent the rendering pass that created the tile. This
has no negative side effects, and it has the advantage that
there is not a single additional loop needed to create these
structures.
With this change, hit detection for lines and points gets very
accurate, because the vector renderer instance keeps track of
line widths and point symbol sizes. After doing a bbox query in
the RTree, returned lines and points are evaluated against the
thresholds of their line width or symbol size. The KML example
with its different symbolizers now has getFeatureInfo too to
show this in action.
This method is an entry point for getting feature information.
Renderers can use a hit canvas or defer to a layer (source) to
get matching features for a pixel.
For now this is only implemented for vector layers, and it uses
a bbox query because we cannot refine the result because of
missing geometry intersection functions yet.
ahocevar
Tom Payne
Frederic Junod
Tim Schaub
Éric Lemoine