MGLLineStyleLayer

@interface MGLLineStyleLayer : MGLVectorStyleLayer

An MGLLineStyleLayer is a style layer that renders one or more stroked polylines on the map.

Use a line style layer to configure the visual appearance of polyline or multipolyline features. These features can come from vector tiles loaded by an MGLVectorTileSource object, or they can be MGLPolyline, MGLPolylineFeature, MGLMultiPolyline, or MGLMultiPolylineFeature instances in an MGLShapeSource or MGLComputedShapeSource object.

You can access an existing line style layer using the -[MGLStyle layerWithIdentifier:] method if you know its identifier; otherwise, find it using the MGLStyle.layers property. You can also create a new line style layer and add it to the style using a method such as -[MGLStyle addLayer:].

Example

let layer = MGLLineStyleLayer(identifier: "trails-path", source: trails)
layer.sourceLayerIdentifier = "trails"
layer.lineWidth = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'exponential', 1.5, %@)",
                           [14: 2,
                            18: 20])
layer.lineColor = NSExpression(forConstantValue: UIColor.brown)
layer.lineCap = NSExpression(forConstantValue: "round")
layer.predicate = NSPredicate(format: "%K == %@", "trail-type", "mountain-biking")
mapView.style?.addLayer(layer)

-initWithIdentifier:source:

Returns a line style layer initialized with an identifier and source.

After initializing and configuring the style layer, add it to a map view’s style using the -[MGLStyle addLayer:] or -[MGLStyle insertLayer:belowLayer:] method.

Declaration

Objective-C

- (nonnull instancetype)initWithIdentifier:(nonnull NSString *)identifier
                                source:(nonnull MGLSource *)source;

Swift

init(identifier: String, source: MGLSource)

Parameters

identifier

A string that uniquely identifies the source in the style to which it is added.

source

The source from which to obtain the data to style. If the source has not yet been added to the current style, the behavior is undefined.

Return Value

An initialized foreground style layer.

Accessing the Layout Attributes

lineCap

The display of line endings.

The default value of this property is an expression that evaluates to butt. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant MGLLineCap values
• Any of the following constant string values:
• butt: A cap with a squared-off end which is drawn to the exact endpoint of the line.
• round: A cap with a rounded end which is drawn beyond the endpoint of the line at a radius of one-half of the line’s width and centered on the endpoint of the line.
• square: A cap with a squared-off end which is drawn beyond the endpoint of the line at a distance of one-half of the line’s width.
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Step functions applied to the $zoomLevel variable

This property does not support applying interpolation functions to the $zoomLevel variable or applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineCap;

Swift

var lineCap: NSExpression! { get set }

lineJoin

The display of lines when joining.

The default value of this property is an expression that evaluates to miter. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant MGLLineJoin values
• Any of the following constant string values:
• bevel: A join with a squared-off end which is drawn beyond the endpoint of the line at a distance of one-half of the line’s width.
• round: A join with a rounded end which is drawn beyond the endpoint of the line at a radius of one-half of the line’s width and centered on the endpoint of the line.
• miter: A join with a sharp, angled corner which is drawn with the outer sides beyond the endpoint of the path until they meet.
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineJoin;

Swift

var lineJoin: NSExpression! { get set }

lineMiterLimit

Used to automatically convert miter joins to bevel joins for sharp angles.

The default value of this property is an expression that evaluates to the float 2. Set this property to nil to reset it to the default value.

This property is only applied to the style if lineJoin is set to an expression that evaluates to miter. Otherwise, it is ignored.

You can set this property to an expression containing any of the following:

• Constant numeric values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineMiterLimit;

Swift

var lineMiterLimit: NSExpression! { get set }

lineRoundLimit

Used to automatically convert round joins to miter joins for shallow angles.

The default value of this property is an expression that evaluates to the float 1.05. Set this property to nil to reset it to the default value.

This property is only applied to the style if lineJoin is set to an expression that evaluates to round. Otherwise, it is ignored.

You can set this property to an expression containing any of the following:

• Constant numeric values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineRoundLimit;

Swift

var lineRoundLimit: NSExpression! { get set }

lineSortKey

Sorts features in ascending order based on this value. Features with a higher sort key will appear above features with a lower sort key.

You can set this property to an expression containing any of the following:

• Constant numeric values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineSortKey;

Swift

var lineSortKey: NSExpression! { get set }

Accessing the Paint Attributes

lineBlur

Blur applied to the line, in points.

This property is measured in points.

The default value of this property is an expression that evaluates to the float 0. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant numeric values no less than 0
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineBlur;

Swift

var lineBlur: NSExpression! { get set }

lineBlurTransition

The transition affecting any changes to this layer’s lineBlur property.

This property corresponds to the line-blur-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineBlurTransition;

Swift

var lineBlurTransition: MGLTransition { get set }

lineColor

The color with which the line will be drawn.

The default value of this property is an expression that evaluates to UIColor.blackColor. Set this property to nil to reset it to the default value.

This property is only applied to the style if linePattern is set to nil. Otherwise, it is ignored.

You can set this property to an expression containing any of the following:

• Constant UIColor values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineColor;

Swift

var lineColor: NSExpression! { get set }

lineColorTransition

The transition affecting any changes to this layer’s lineColor property.

This property corresponds to the line-color-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineColorTransition;

Swift

var lineColorTransition: MGLTransition { get set }

lineDashPattern

Specifies the lengths of the alternating dashes and gaps that form the dash pattern. The lengths are later scaled by the line width. To convert a dash length to points, multiply the length by the current line width. Note that GeoJSON sources with lineMetrics: true specified won’t render dashed lines to the expected scale. Also note that zoom-dependent expressions will be evaluated only at integer zoom levels.

This property is measured in line widths.

This property is only applied to the style if linePattern is set to nil. Otherwise, it is ignored.

This attribute corresponds to the line-dasharray layout property in the GL Style Specification.

You can set this property to an expression containing any of the following:

• Constant array values no less than 0
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Step functions applied to the $zoomLevel variable

This property does not support applying interpolation functions to the $zoomLevel variable or applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineDashPattern;

Swift

var lineDashPattern: NSExpression! { get set }

lineDashPatternTransition

The transition affecting any changes to this layer’s lineDashPattern property.

This property corresponds to the line-dasharray-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineDashPatternTransition;

Swift

var lineDashPatternTransition: MGLTransition { get set }

lineGapWidth

Draws a line casing outside of a line’s actual path. Value indicates the width of the inner gap.

This property is measured in points.

The default value of this property is an expression that evaluates to the float 0. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant numeric values no less than 0
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineGapWidth;

Swift

var lineGapWidth: NSExpression! { get set }

lineGapWidthTransition

The transition affecting any changes to this layer’s lineGapWidth property.

This property corresponds to the line-gap-width-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineGapWidthTransition;

Swift

var lineGapWidthTransition: MGLTransition { get set }

lineGradient

The color gradient with which the line will be drawn. This property only has an effect on lines defined by an MGLShapeSource whose MGLShapeSourceOptionLineDistanceMetrics option is set to YES.

This property is only applied to the style if lineDasharray is set to nil, and linePattern is set to nil, and the data source requirements are met. Otherwise, it is ignored.

You can set this property to an expression containing any of the following:

• Constant UIColor values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $lineProgress variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineGradient;

Swift

var lineGradient: NSExpression! { get set }

lineOffset

The line’s offset. For linear features, a positive value offsets the line to the right, relative to the direction of the line, and a negative value to the left. For polygon features, a positive value results in an inset, and a negative value results in an outset.

This property is measured in points.

The default value of this property is an expression that evaluates to the float 0. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant numeric values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineOffset;

Swift

var lineOffset: NSExpression! { get set }

lineOffsetTransition

The transition affecting any changes to this layer’s lineOffset property.

This property corresponds to the line-offset-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineOffsetTransition;

Swift

var lineOffsetTransition: MGLTransition { get set }

lineOpacity

The opacity at which the line will be drawn.

The default value of this property is an expression that evaluates to the float 1. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant numeric values between 0 and 1 inclusive
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineOpacity;

Swift

var lineOpacity: NSExpression! { get set }

lineOpacityTransition

The transition affecting any changes to this layer’s lineOpacity property.

This property corresponds to the line-opacity-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineOpacityTransition;

Swift

var lineOpacityTransition: MGLTransition { get set }

linePattern

Name of image in style images to use for drawing image lines. For seamless patterns, image width must be a factor of two (2, 4, 8, …, 512).

You can set this property to an expression containing any of the following:

• Constant string values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *linePattern;

Swift

var linePattern: NSExpression! { get set }

linePatternTransition

The transition affecting any changes to this layer’s linePattern property.

This property corresponds to the line-pattern-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition linePatternTransition;

Swift

var linePatternTransition: MGLTransition { get set }

lineTranslation

The geometry’s offset.

This property is measured in points.

The default value of this property is an expression that evaluates to an NSValue object containing a CGVector struct set to 0 points rightward and 0 points downward. Set this property to nil to reset it to the default value.

This attribute corresponds to the line-translate layout property in the GL Style Specification.

You can set this property to an expression containing any of the following:

• Constant CGVector values
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable

This property does not support applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineTranslation;

Swift

var lineTranslation: NSExpression! { get set }

lineTranslationTransition

The transition affecting any changes to this layer’s lineTranslation property.

This property corresponds to the line-translate-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineTranslationTransition;

Swift

var lineTranslationTransition: MGLTransition { get set }

lineTranslationAnchor

Controls the frame of reference for lineTranslation.

The default value of this property is an expression that evaluates to map. Set this property to nil to reset it to the default value.

This property is only applied to the style if lineTranslation is non-nil. Otherwise, it is ignored.

This attribute corresponds to the line-translate-anchor layout property in the GL Style Specification.

You can set this property to an expression containing any of the following:

• Constant MGLLineTranslationAnchor values
• Any of the following constant string values:
• map: The line is translated relative to the map.
• viewport: The line is translated relative to the viewport.
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Step functions applied to the $zoomLevel variable

This property does not support applying interpolation functions to the $zoomLevel variable or applying interpolation or step functions to feature attributes.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineTranslationAnchor;

Swift

var lineTranslationAnchor: NSExpression! { get set }

lineWidth

Stroke thickness.

This property is measured in points.

The default value of this property is an expression that evaluates to the float 1. Set this property to nil to reset it to the default value.

You can set this property to an expression containing any of the following:

• Constant numeric values no less than 0
• Predefined functions, including mathematical and string operators
• Conditional expressions
• Variable assignments and references to assigned variables
• Interpolation and step functions applied to the $zoomLevel variable and/or feature attributes

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite, null_resettable)
NSExpression *lineWidth;

Swift

var lineWidth: NSExpression! { get set }

lineWidthTransition

The transition affecting any changes to this layer’s lineWidth property.

This property corresponds to the line-width-transition property in the style JSON file format.

Declaration

Objective-C

@property (nonatomic, assign, unsafe_unretained, readwrite)
MGLTransition lineWidthTransition;

Swift

var lineWidthTransition: MGLTransition { get set }