At the moment, the annotations implementation in the `mapbox-gl-native`
core is creating concrete layer instances apart from `LayerManager/LayerFactory`
code path.
So, annotations must be disabled if the `LayerManager` implementation does
not provide line, fill or symbol layers (those, used by the annotations).
Note: in future, annotations implementation will be moved from the core to the
platform SDK level(see https://github.com/mapbox/mapbox-plugins-android/tree/master/plugin-annotation)
and `LayerManager` won't need to disable it.
`LayerManager` is now responsible for `RenderLayer` instances creation,
so that there is a single entry point for creating of objects, which
correspond to a certain layer type.
The `LayerType type` field is dropped from `Layer::Impl`.
The `LayerTypeInfo` contains static meta data about certain layer type.
Each layer module should have a single immutable `LayerTypeInfo` instance
for the represented layer type. Both `LayerImpl` and `LayerFactory` from the
module always refer to the same `LayerTypeInfo` instance, so address of this
instance can be used as a layer module Id during the process life time.
This patch introduces the initial implementation of
- A `LayerFactory` abstract class that creates `style::Layer` instances of
a certain layer type (line, hillshade, round, ..)
- A singleton `LayerManager` class, which is responsible for initializing
the `LayerFactory` instances and forwarding the `create()` calls to the
corresponding factory.
The `style::Layer` class now exposes all the properties contained at `style::LayerImpl`.
This allowed to drop `style::Layer::accept()` method usage, avoid the repeated generated code
and thus save some binary size.
This patch is a part of the layers modularization effort.
Avoid dangling references in the following sequence:
auto& id = layer->getID();
layer->setMaxZoom(2);
std::cout << id;
The reference would be dangling because mutating the layer allocates a new Immutable impl, and there may be no references to the prior impl, which held the id.
* Layer source ID is immutable; must be provided to the constructor
* Layer source layer is mutable
* Layers with GeoJSON sources do not have a source layer
While here, make Layer::copy impl-private.
