- Multi-platform graphics engine based on OpenGL for Android and Metal for iOS
- Touch and gesture handling
- Tiled Map Layers
- Polygon Layers
- Icon Layers
...and more to come! See our roadmap at openmobilemaps.io
To support both the Android and iOS, most of the code-base is written in C++ and shared between the two platforms. The Kotlin and Swift interface bindings are generated with a fork of the Djinni library. The library intentionally is designed to have a modular structure, so that most parts of it can be adjusted or completely replaced with custom implementations. Most of the interfaces are also exposed to Swift and Kotlin, so extensions can also conveniently be programmed in those languages.
The internal structure of the project is split into two main modules: the graphics-core and the maps-core. While the first implements a generic structure for rendering basic graphic primitives on Android and iOS, the latter is a collection of classes that provide the basics for creating a digital map.
The rendering concept in the graphics core is built around generic graphics primitives to achieve a versatile base structure. While the basic logic for organizing the primitives is shared, the implementations of those graphics object interfaces are platform-specific. For Android, the OpenGL code is kept in C++, while the Metal-implementations for iOS are written in Swift. The SceneInterface is the shared, central collection of the necessary interfaces for both creating and rendering such graphics objects.
Building on top of the graphics core, the MapCore wraps the generic render code into a more accessible collection of higher-level classes with the functionality to build and display a digital map.
On both platforms, the MapView builds the central ui element that can directly be added to the app and be interacted with. It handles the interactions between each platform and the shared library, the lifecycle of the view, as well as setting up relevant platform-specific components and exposing the necessary methods for manipulating all elements of the map.
The MapScene, implementing the MapInterface, holds the necessary resources for interacting with the underlying render system and creating the graphics primitives, but also builds the main access point for the other components that are relevant for a functioning map. For instance, the map requires a configuration file, a camera, a touch handler and others. The MapScene also holds the collection of all layers in the scene and provides the necessary methods to adjust it.
When setting up the map, a coordinate system for it needs to be specified. In the current implementation, the system is assumed to be a uniform, two-dimensional grid.
All map positions handled within maps core are of the type Coord. Along with the three-dimensional position values, it holds a coordinate system identifier with the purpose of specifically exposing to the system in which the values should be interpreted at that time. To switch between different coordinate systems, the MapScene holds a CoordinateConversionHelper. This helper uses pre-defined and additionally registered custom converters to transform coordinates between two systems, specified by their system identifier.
This library comes with the implementations for two prominent coordinate systems: EPSG:2056 (LV95/LV03+) and EPSG:3857 (Pseudo-Mercator). They can be created using the CoordinateSystemFactory.
The camera attached to the MapScene defines the section of the map that is rendered when a frame is drawn. It also handles and interprets interaction events passed to it by a TouchHandler. MapCore contains an implementation for a simple orthographic camera moving in the x/y-plane and a DefaultTouchHandler for a matching gesture recognition. The camera component offers an interface for querying and setting its current position in the space defined by the map's coordinate system.
The graphical content displayed in the MapScene is grouped in layers. A layer contains one to many LayerObjects. These are collections of the information necessary to place a graphics primitive in the maps coordinate space and that define their appearance. Before a new frame is drawn, the MapScene queries all added layers for a configuration, specifying which graphics need to be drawn in which respective order.
Two layer types are available with MapCore: Tiled2dMapRasterLayer and PolygonLayer.
The content of most digital maps is split into hierarchical layers of map tiles. This layer supports both the loading and displaying of the relevant tiles for a given camera position and zoom-value. On creation of such a layer, a Tiled2dMapLayerConfig needs to be defined. It specifies the layers coordinate system by setting the bounds coordinates, as well as the different zoom layers and provides the url/identifier for loading the tiles.
In addition to the configuration, an implementation of the TextureLoaderInterface needs to be supplied. A default implementation to load tiles from a given URL is contained in maps core on both platforms.
The PolygonLayer provides an interface to create and draw uniformly colored polygons in the map space.
This project is licensed under the terms of the MPL 2 license. See the LICENSE file.