Unofficial Mapbox GL Native bindings for Qt QML: API

This is a description of an API that was written for platforms lacking QtLocation 5.9 support. I would like to acknowledge the use of QtLocation 5.9 Mapbox GL plugin documentation while this API documentation.

API consists of two items: MapboxMap for displaying the map and MapboxMapGestureArea that can be used within MapboxMap for interacting with it.

QQuickItemMapboxGL (C++) / MapboxMap (QML)

QML Quick Item for displaying maps using Mapbox GL. See qquickitemmapboxgl.h for specific syntax, if needed.

In QML, MapboxMap type is defined by this plugin. In C++, use QQuickItemMapboxGL class.

Include statements

In QML

import MapboxMap 1.0

In C++

#include <qquickitemmapboxgl.h>

General comments

This Mapbox GL interface is written to keep map properties, sources, layers, and properties persistent to the style changes. In particular, all sources, layers, paint and layer properties that were introduced via add* or update* methods will be re-added to the map when changing styles until they are removed using remove* methods.

When using GeoJSON sources, note that there is a difference in the order of coordinates when using GeoJSON and Qt native representation. Here, the methods accepting coordinates as explicit arguments, such as updateSourcePoint, use the same order as in Qt.

As an example of the use of this API, see QML file app/qml/main.qml in this repository.

Properties

Map properties are classified and listed in the following sub-sections. Each property is given with the corresponding type in front of it.

Map settings on initialization

The properties in this subsection should be set on initialization of the map. If modified later, the properties may not be applied until the map's frame buffer object is recreated. Some of them (such as cache-related properties) would be used as they were specified for the first created map.

string accessToken When hosted vector tiles and styles require an API access token, you can specify them using accessToken. For example , for Mapbox you can obtain it from the Mapbox account page. Access tokens associate requests to Mapbox's vector tile and style APIs with your Mapbox account. They also deter other developers from using your styles without your permission.
string apiBaseUrl The API base URL is the URL that the mapbox:// protocol will be resolved to. It defaults to "https://api.mapbox.com" but can be changed, for instance, to a tile cache server address.
string assetPath Returns the asset path, which is the root directory from where the asset:// scheme gets resolved in a style. asset:// can be used for loading a resource from the disk in a style rather than fetching it from the network.

By default, it is set to the value returned by QCoreApplication::applicationDirPath().
bool cacheDatabaseDefaultPath When set to true, the path of the cache database is named mapboxgl-qml-cache.db and is stored at QStandardPaths::CacheLocation. Set to false by default.

See also general comment regarding cache settings given in the description of cacheDatabasePath.
int cacheDatabaseMaximalSize Returns the cache database maximum hard size in bytes. The database will grow until the limit is reached. Setting a maximum size smaller than the current size of an existing database results in undefined behavior

By default, it is set to 50 MB.

See also general comment regarding cache settings given in the description of cacheDatabasePath.
string cacheDatabasePath Returns the cache database path. The cache is used for storing recently used resources like tiles and also an offline tile database pre-populated by the Offline Tool.

By default, it is set to :memory: meaning it will create an in-memory cache instead of a file on disk.

Cache-related settings are shared between all QMapboxGL instances because different maps will share the same cache database file. The first map to configure cache properties such as size and path will force the configuration to all newly instantiated QMapboxGL objects.
bool cacheDatabaseStoreSettings When set to true, cache database settings will be preserved between runs and, on initialization, loaded from configuration file using QSettings. At present, this concerns only cache maximal size.
qrealdevicePixelRatio Device pixel ratio that is used during construction of the map widget. This should correspond to the true physical to logical pixel ratio as given in Qt via devicePixelRatio method of QScreen. This property allows sharp rendering of the widget in HiDPI cases if the rendering through framebuffer is used (see useFBO). For direct rendering case (useFBO=false), devicePixelRatio is not used.

If devicePixelRatio is not specified, it is determined on the basis of the parent QQuickItem, or if absent, on the basis of the primary screen.

See also pixelRatio that can be changed after the widget is constructed.
bool useFBO When set to true (default), Mapbox GL will use a framebuffer object to render a map. When set to false, the map is rendered issuing OpenGL commands directly, through a QSGRenderNode. This is supported only for platforms starting with Qt version 5.8.

Map rendering

real bearing The map bearing angle in degrees. Negative values and values over 360 are valid and will wrap. The direction of the rotation is counterclockwise.

When center is defined, the map will rotate around the center pixel coordinate respecting the margins if defined.
QGeoCoordinate center Coordinates of the map center. Centers the map at a geographic coordinate respecting the margins, if set.

In QML, use QtPositioning.coordinate(latitude, longitude) construct (see http://doc.qt.io/qt-5/qml-coordinate.html and http://doc.qt.io/qt-5/qgeocoordinate.html for details).
real mapToQtPixelRatio Ratio between logical map and Qt pixel sizes. When wishing to add elements on a map which should have a fixed size in relation to other Qt UI elements, use this property to when specifying sizes in map styles. For example, when adding icons to the map.
rect margins Relative margins that determine position of the center on the map. Margins specify the relative active area of the widget and the position of the active area. When given by a rectangle (x, y, width, height), the margins are specified by the active area with the left bottom given by x and y as well as the size of the active area as specified by width and height.

For example, margins given with the rectangle (0.1, 0.2, 0.8, 0.3) would correspond to the active area that is shifted 0.1*width from the left, 0.2*height up from the bottom, is 0.8*width wide leaving 0.1*width pixels to the right margin, and is 0.3*height high leaving the top half of the widget as a margin. Through use of the margins one can shift the center within the widget and ensure that it is not covered by other GUI elements drawn on the top of the map, for example.
real maximumZoomLevel Maximum zoom level allowed for the map.
real minimumZoomLevel Minimum zoom level allowed for the map.
real pitch Pitch toward the horizon measured in degrees, with 0 resulting in a two-dimensional map. It is constrained at 60 degrees.
real pixelRatio Relative pixel density of the screen when compared to 96dpi. All the map elements will be scaled by this ratio when drawn. This allows to use the same style on the screens with the different pixel densities and adjust the scale on fly. Note that the minimal pixelRatio is set to devicePixelRatio used at the map widget construction.

It is recommended to use this property for adjusting map overall zoom for HiDPI cases. However, do not assume relationships between Qt and map logical pixel sizes as it will depend on selected implementation of the rendering and may change in future. Instead, for adding custom elements through map styles, use the properties made for such conversion: mapToQtPixelRatio, metersPerPixel, metersPerMapPixel.
string styleJson The map style in JSON given as a string. Sets a new style from a JSON that must conform to the Mapbox style specification. If the style is loaded via URL, one can track changes in styleJson and adjust it via setting to a new value for runtime styling in QML. For example, replacing all {name_en} to some other supported language indicator would allow to change the language of the map.
string styleUrl The map style URL. Sets a URL for fetching a JSON that will be later fed to setStyleJson. URLs using the Mapbox scheme (mapbox://) are also accepted and translated automatically to an actual HTTPS request.

The Mapbox scheme is not enforced and a style can be fetched from anything that QNetworkAccessManager can handle.

Note that all given URLs can be altered before fetching from internet, as described below under Mangling of URLs.
real zoomLevel The map zoom factor. This property is used to zoom the map.

Mangling of URLs

Before fetching resources from internet, URLs can be either printed for debugging purposes or changed by adding them given suffix.

bool urlDebug When set to true, all URLs are printed out in stdout before fetching them.
string urlSuffix When set, this string will be appended to all URLs before fetching them online. For example, you can append your server's specific api key by setting urlSuffix to ?apikey=ABCD if it has to be specified in such format at the end of each requested URL.

Other properties

string errorString Current error string. Please note that this property is not covering all possible errors in the API. When set, it is never cleared. Thus, please connect to the signal errorChanged to trigger error processing and don't rely on clearance of errorString property.
real metersPerPixel Meters per Qt logical pixel at the center of the map.
real metersPerMapPixel Meters per map logical pixel at the center of the map. Use this property when drawing objects on the map that are specified in pixels, such as map style, and can be then converted to meters. For example, when drawing location precision with a circle by giving its radius in map pixels.
real metersPerPixelTolerance Tolerance with which metersPerPixel is updated.

Queries and Signals

Several properties of the map can be queried via signals. This relatively complicated way of querying the properties is induced to ensure thread-safety of the queries.

In general, the queries consist of a method that is called to initiate it and a signal that is emitted by the map object with the response to the query. Query can carry an id or a tag that can be used to filter only the responses that are of interest.

void querySourceExists(const QString id)

signal replySourceExists(const QString id, bool exists)

Query whether the source with given id exists.
void queryLayerExists(const QString id)

signal replyLayerExists(const QString id, bool exists)

Query whether the layer with given id exists.
void queryCoordinateForPixel(const QPointF p, const QVariant &tag = QVariant())

signal replyCoordinateForPixel(const QPointF pixel, QGeoCoordinate geocoordinate, qreal degLatPerPixel, qreal degLonPerPixel, const QVariant &tag)

Query geographical location geocoordinate for a position in the widget given as a pixel coordinates p. For bookkeeping purposes, tag of any type supported by QVariant can be added. In addition to geocoordinates, an approximated sensitivity of geocoordinate changes to pixel coordinates are given by degLatPerPixel and degLonPerPixel. degLatPerPixel and degLonPerPixel can be used to process mouse clicks by the user to decide whether the user pressed a certain location within few pixels from it or not.

For example, the following code will compare the geographical location returned by the signal to the current position and run a specific method if it was deemed to be nearby:
```
  // 15 pixels at 96dpi would correspond to 4 mm
  var nearby_lat = 15 * degLatPerPixel;
  var nearby_lon = 15 * degLonPerPixel;

  // check if its current position
  if ( Math.abs(coordinate.longitude - map.position.coordinate.longitude) < nearby_lon &&
  	Math.abs(coordinate.latitude - map.position.coordinate.latitude) < nearby_lat ) {
      positionMarker.mouseClick();
      return;
  }
```

Methods

Map methods are classified and listed in the following sub-sections.

General methods

void clearCache()

Deletes all data from the current cache database. In addition to performing DELETE statements, VACUUM is performed to recover the storage.
QVariantList defaultStyles() const

List of default Mapbox styles returned as a JSON array
void fitView(const QVariantList &coordinates, bool preserve = false)

Finds zoom and the center that would allow to fit the given list of coordinates in the map view taking into account current margins, pitch, and bearing. Note that the expected list elements are coordinates as given by QGeoCoordinate (QtPositioning.coordinate in QML). For example, to fit Helsinki and Tallinn on a map, use
```
   map.fitView([QtPositioning.coordinate(60.170448, 24.942046),
  	  QtPositioning.coordinate(59.436962, 24.753574)])
```
Optionally, it can fit the given list if preserve is set to true. This will compensate changes in margins or map size to ensure that the given coordinates are visible. Such automatic fit can be stopped either by user interaction (pan, change of center, zoom, bearing, or pitch) or by calling stopFitView.

When only one coordinate is given in coordinates, the given coordinate will be centered if it falls out of the current margins. As with the list, preserve can be used to make it automatic until disabled.
void pan(int dx, int dy)

Pan the map by dx, dy pixels.
void setMargins(qreal left, qreal top, qreal right, qreal bottom)

Margins are given relative to the widget width (left and right margin) and height (top and bottom). By default, the margins are 0 for all. In this case, the given center will be on the center of the widget. To shift the center to the bottom by 25%, set the top margin to 0.5. Then the center will be found between the middle line and the bottom. Margins allow to switch between navigation and browsing mode, for example.

See also property margins for description on how to set margins using active area described by rectangle.
void setZoomLevel(qreal zoomLevel, const QPointF &center = QPointF())

Method to set zoomLevel that can be used with the defined center (pixel coordinates on the widget) to keep the given center position unchanged while zooming the map. This function could be used for implementing a pinch gesture or zooming by using the mouse scroll wheel.
void stopFitView()

Stops automatic fit to view. See fitView and its argument preserve for description.

Map sources

Map sources can be added, updated, and removed. Note that, since in Mapbox GL update would automatically add source when such source is absent, addition and update in these bindings use internally update methods of QMapboxGL and can be considered synonyms withing this API.

void addSource(const QString &sourceID, const QVariantMap& params)

Adds a source id to the map as specified by the Mapbox style specification with params. For example, GeoJSON type can be used to specify road, position on the map, or many other features that can added and later modified by application.

The following QML snippet adds a point on the map

	map.addSource("location",
		  {"type": "geojson",
		      "data": {
			  "type": "Feature",
			  "properties": { "name": "location" },
			  "geometry": {
			      "type": "Point",
			      "coordinates": [
				  (24.94),
				  (60.16)
			      ]
			  }
		      }
		  })

and the following QML snippet adds a small line source

    var routeSource = {
	"type": "geojson",
	"data": '{
	    "type": "Feature",
	    "properties": {},
	    "geometry": {
		"type": "LineString",
		"coordinates": [
		    [24.942046, 60.170448],
		    [
			24.934420000000003,
			60.163500000000006
		    ],
		    [
			24.923490008921945,
			60.16159500239787
		    ],
		    [
			24.916150000000002,
			60.171530000000004
		    ],
		    [
			24.931620000000002,
			60.18218
		    ],
		    [
			24.961660000000002,
			60.17557000000001
		    ],
		    [
			24.954860000000004,
			60.158930000000005
		    ],
		    [
			24.943690000000004,
			60.155280000000005
		    ]
		]
	    }
	}'
    }

    map.addSource("route", routeSource)

Notice that the data component for GeoJSON can be given either as a string or a JSON object.

void addSourceLine(const QString &sourceID, const QVariantList &coordinates, const QString &name = QString())

Constructs and adds line source to the map. Source description is constructed in GeoJSON format with the given sourceID as a LineString, coordinates given as a list of QGeoCoordinate objects, and, if specified, property name.
void addSourcePoint(const QString &sourceID, const QGeoCoordinate &coordinate, const QString &name = QString())

void addSourcePoint(const QString &sourceID, qreal latitude, qreal longitude, const QString &name = QString())

Constructs and adds source to the map consisting of a single point. Source description is constructed in GeoJSON format with the given sourceID, coordinates, and, if specified, property name.
void addSourcePoints(const QString &sourceID, const QVariantList &coordinates, const QVariantList &names = QVariantList())

Constructs and adds source to the map consisting of a list of points. Source description is constructed in GeoJSON format with the given sourceID as a FeatureCollection, coordinates given as a list of QGeoCoordinate objects, and, if specified, names for each of the points as a list of strings encoded in GeoJSON as a properties for each of the points. For example, this method together with the corresponding layer could be used to add POIs to the map.
void updateSource(const QString &sourceID, const QVariantMap& params)

Update source given by sourceID. If absent, the corresponding source will be added. See addSource for the description of the arguments.
void updateSourceLine(const QString &sourceID, const QVariantList &coordinates, const QString &name = QString())

Update source given by sourceID. If absent, the corresponding source will be added. See addSourceLine for the description of the arguments.
void updateSourcePoint`(const QString &sourceID, const QGeoCoordinate &coordinate, const QString &name = QString())

void updateSourcePoint(const QString &sourceID, qreal latitude, qreal longitude, const QString &name = QString())`

Update source given by sourceID. If absent, the corresponding source will be added. See addSourcePoint for the description of the arguments.
void updateSourcePoints(const QString &sourceID, const QVariantList &coordinates, const QVariantList &names = QVariantList())

Update source given by sourceID. If absent, the corresponding source will be added. See addSourcePoints for the description of the arguments.
void removeSource(const QString &sourceID)

Remove the source with sourceID from the map. This method has no effect if the source does not exist.

Map layers

Map layers can be added or removed.

void addLayer(const QString &id, const QVariantMap &params, const QString& before = QString())

Adds a style layer with id to the map as specified by the Mapbox style specification with params. The layer will be added under the layer specified by before, if specified. Otherwise it will be added as the topmost layer.

If the layer with such id already exists, the old layer will be removed and it will be replaced with the layer specified here.
void removeLayer(const QString &id)

Removes the layer with given id.
void addImage(const QString &name, const QImage &sprite)

Add image with name given by QImage sprite. After addition of the image, it can be referred to by its name in the layer or paint properties.
bool addImagePath(const QString &name, const QString &path, int svgX=-1, int svgY=-1)

Add image using image file path or url starting with file://. For example, this can be used to specify the image in QML as in
```
map.addImagePath("position-icon", Qt.resolvedUrl("icons/position"))
```
The method can load and render SVGs (determined by file extension "svg") using the size provided via svgX and svgY. If only svgX is given, it is assumed that svgY=svgX. If none of the sizes are given and file is assumed to be SVG, it is rendered to 32x32 pixels.

The method would return true if image was found and loaded by Qt.
void removeImage(const QString &name)

Remove image specified by name.

Map layout and paint properties

void setLayoutProperty(const QString &layer, const QString &property, const QVariant &value)

void setLayoutPropertyList(const QString &layer, const QString &property, const QVariantList &value)

Sets a layout property value to an existing layer. The property string can be any as defined by the Mapbox style specification for layout properties. Use setLayoutPropertyList when the property value is given by the list, such as text-offset, for example.
void setPaintProperty(const QString &layer, const QString &property, const QVariant &value)

void setPaintPropertyList(const QString &layer, const QString &property, const QVariantList &value)

Sets a paint property value to an existing layer. The property string can be any as defined by the Mapbox style specification for layout properties. Use setPaintPropertyList when the property value is given by the list, such as text-translate, for example.

Tracking locations on the map

To allow tracking position of certain locations on the widget, a set of methods and signals are available. This allows to draw interactive QML items on the top of the certain geographical location shown on the map and change the location of QML items on the screen and their visibility in response to the map movement, rotation, and pitch changes.

void trackLocation(const QString &id, const QGeoCoordinate &coordinates)

Register new location given by its coordinates using id. If there was a location registered for tracking with the same id, its coordinates will be replaced by the coordinates given here.

On the first update and the change of the position on screen, signal locationChanged is emitted.
void removeLocationTracking(const QString &id)

Remove location id from tracking. On removal, signal locationTrackingRemoved is emitted.
void removeAllLocationTracking()

Remove tracking for all locations. No signals are emitted in this case.
signal locationChanged(QString id, bool visible, const QPoint pixel)

On the change of location position in the widget or its visibility, locationChanged signal is emitted specifying id of the tracked location, its visibility given by visible, and location in the widget given by pixel.
signal locationTrackingRemoved(QString id)

When location tracking is removed through removeLocationTracking, this signal is emitted specifying the removed location id.

MapboxMapGestureArea

MapboxMapGestureArea is intended to be used within MapboxMap for mouse and touch interaction. On construction, MapboxMapGestureArea property map should be given MapboxMap id for interaction with the map.

Example of MapboxMapGestureArea use is shown below

    MapboxMap {
	id: map
	anchors.fill: parent

	MapboxMapGestureArea {
	    id: mouseArea
	    map: map
	    activeClickedGeo: true
	    activeDoubleClickedGeo: true
	    activePressAndHoldGeo: true

	    onClicked: console.log("Click: " + mouse)
	    onDoubleClicked: console.log("Double click: " + mouse)
	    onPressAndHold: console.log("Press and hold: " + mouse)

	    onClickedGeo: console.log("Click geo: " + geocoordinate + " sensitivity: " + degLatPerPixel + " " + degLonPerPixel)
	    onDoubleClickedGeo: console.log("Double click geo: " + geocoordinate + " sensitivity: " + degLatPerPixel + " " + degLonPerPixel)
	    onPressAndHoldGeo: console.log("Press and hold geo: " + geocoordinate + " sensitivity: " + degLatPerPixel + " " + degLonPerPixel)
	}
    }

Signals

Emitted signals follow the signals emitted by MouseArea. In addition to regular MouseArea signals forwarded by MapboxMapGestureArea, there are similar signals that forward geographical coordinates at which user performed a click, double click, or pressed and hold the mouse. To enable signals with geographical coordinates, a corresponding property has to be set to true (see description of properties below). Note that finding geographical coordinates corresponding to the event requires some additional processing by the map object and, if not used, is recommended to be left disabled.

For regular MouseArea signals, see Qt documentation.

clicked(MouseEvent mouse)

doubleClicked(MouseEvent mouse)

pressAndHold(MouseEvent mouse)

In addition to regular MouseArea signals, geographical coordinate at which user has interacted with the map and its sensitivity is forwarded via the following signals:

clickedGeo(var geocoordinate, real degLatPerPixel, real degLonPerPixel)

doubleClickedGeo(var geocoordinate, real degLatPerPixel, real degLonPerPixel)

pressAndHoldGeo(var geocoordinate, real degLatPerPixel, real degLonPerPixel)

In these signals, geocoordinate is QtPositioning.coordinate object. See description of replyCoordinateForPixel signal of MapboxMap for the description of degLatPerPixel and degLonPerPixel values.

Properties

var map Map object to be interacted with through the gesture area. This property must be set on construction.
bool activeClickedGeo If true, clickedGeo signal will be emitted after a click event. False by default.
bool activeDoubleClickedGeo If true, doubleClickedGeo signal will be emitted after a double click event. False by default.
bool activePressAndHoldGeo If true, pressAndHoldGeo signal will be emitted after a double click event. False by default.
boolintegerZoomLevels If true, the result of pinch-zoom will snap to integer zoom levels, which should look better with raster sources in terms of sharpness and level of detail. False by default.

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api.md

api.md

Unofficial Mapbox GL Native bindings for Qt QML: API

Table of Contents

QQuickItemMapboxGL (C++) / MapboxMap (QML)

Include statements

General comments

Properties

Map settings on initialization

Map rendering

Mangling of URLs

Other properties

Queries and Signals

Methods

General methods

Map sources

Map layers

Map layout and paint properties

Tracking locations on the map

MapboxMapGestureArea

Signals

Properties

Files

api.md

Latest commit

History

api.md

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Unofficial Mapbox GL Native bindings for Qt QML: API

Table of Contents

QQuickItemMapboxGL (C++) / MapboxMap (QML)

Include statements

General comments

Properties

Map settings on initialization

Map rendering

Mangling of URLs

Other properties

Queries and Signals

Methods

General methods

Map sources

Map layers

Map layout and paint properties

Tracking locations on the map

MapboxMapGestureArea

Signals

Properties