[android] Add support for data driven styling

[ivovandongen]

Adds support for data driven styling to the Android SDK.

TODO:

Functions

• Camera (Zoom)
  • Exponential
  • Interval
  • Unit tests
• Source (Property)
  • Categorical
  • Exponential
  • Identity
  • Interval
  • Unit tests
• Composite (ZoomAndProperty)
  • Categorical
  • Exponential
  • Interval
  • Unit tests

Other:

• Merge Property and PropertyValue
• Test activity/examples
• JavaDoc

[mention-bot]

@ivovandongen, thanks for your PR! By analyzing this pull request, we identified @incanus and @jfirebaugh to be potential reviewers.

[ivovandongen]

@mapbox/android I've restored support for exponential zoom functions on this branch and set up the basis for the property / zoom-and-property functions. For this I adhered to the naming in the style spec and not the core naming. So, for example, ZoomFunction and not CameraFunction.

[ivovandongen]

After the discussion yesterday I've re-implemented the functions and stops with typed stops in 0a28d4d. Overall, I think it looks good.

We now have:

Functions:

• CameraFunction
• SourceFunction - Contains the referenced property
• CompositeFunction (not implemented yet)

Stops:

• CategoricalStops (not implemented yet)
• ExponentialStops - Contains base, stops (and soon colorSpace)
• IdentityStops - Empty, marker class
• IntervalStops - Contains stops

The DSL is spread out in Function, Stop and Stops and looks like this for CameraFunctions (exponential):

    //Set
    layer.setProperties(
      fillOpacity(
        zoom(
          exponential(
            0.5f,
            stop(2, fillOpacity(0.3f))
          )
        )
      )
    );

    //Get
    float base = ((ExponentialStops) layer.getFillOpacity().getFunction().getStops()).getBase();
    Stop[] stops = ((ExponentialStops) layer.getFillOpacity().getFunction().getStops()).stops;

And like this for SourceFunctions (identity):

    //Set
    layer.setProperties(
      fillOpacity(property("FeaturePropertyA", Stops.<Float>identity()))
    );

    //Get
    String property = ((SourceFunction) layer.getFillOpacity().getFunction()).getProperty();

The typing is a little uncomfortable when interrogating the style. Suggestions are welcome.

[tobrun]

API looks great, can't think of a simpler construction as the proposed DSL.

[ivovandongen]

I've implemented the composite functions (unit test generation forthcoming). The DSL for composite functions looks similar to the style spec format for Zoom-And-Property functions:

      fillOpacity(
        composite(
          "FeaturePropertyA",
          exponential(
            0.5f,
            stop(0, 0.3f, fillOpacity(1f)),
            stop(0, 0.5f, fillOpacity(0.3f)),
            stop(1, 0.3f, fillOpacity(1f)),
            stop(1, 0.5f, fillOpacity(0.3f))
          )
        )
      )

Where there is only one stops implementation for all zoom levels.

An alternative which is closer to the representation in the core implementation and the proposal for function revision:

    layer.setProperties(
      fillOpacity(
        composite(
          "FeaturePropertyA",
          stop(0,
            exponential(
              0.5f,
              stop(0.3f, fillOpacity(1f)),
              stop(0.5f, fillOpacity(0.3f))
            )
          ),
          stop(1,
            exponential(
              0.5f,
              stop(0.3f, fillOpacity(1f)),
              stop(0.5f, fillOpacity(0.3f))
            )
          )
        )
      )

This offers more flexibility, but is also more verbose.

The data representation follows the core and stores a Stops implementation per zoom level instead of a list with composite keys (eg Stop<CompositeValue<Z, I>, O>). This involves a awkward conversion step internally as the conversion templates expect the latter format for compatibility with the spec, but this can be optimised later if needed.

In addition, I made some changes to the Stops classes and added a IterableStops abstract base class so it is easier to access the actual stops collections without code like getStops().getStops().length (now getStops().size()). This does involve some generics acrobatics:

CompositeStops<Float, Float, Float, ExponentialStops<Float, Float>> stops = (CompositeStops<Float, Float, Float, ExponentialStops<Float, Float>>) layer.getFillOpacity().getFunction().getStops();

[ivovandongen]

@jfirebaugh Finished up on this. After reviews, shall I merge it back into the dds-wip branch?