OpenLayers.Renderer.Canvas

A renderer based on the 2D ‘canvas’ drawing element.

Inherits

OpenLayers.Renderer

Summary

OpenLayers.Renderer.Canvas	A renderer based on the 2D ‘canvas’ drawing element.
Properties
hitDetection	{Boolean} Allow for hit detection of features.
hitOverflow	{Number} The method for converting feature identifiers to color values supports 16777215 sequential values.
canvas	{Canvas} The canvas context object.
features	{Object} Internal object of feature/style pairs for use in redrawing the layer.
pendingRedraw	{Boolean} The renderer needs a redraw call to render features added while the renderer was locked.
cachedSymbolBounds	{Object} Internal cache of calculated symbol extents.
Constructor
OpenLayers.Renderer.Canvas
Functions
setExtent	Set the visible part of the layer.
eraseGeometry	Erase a geometry from the renderer.
supported	{Boolean} Whether or not the browser supports the renderer class
setSize	Sets the size of the drawing surface.
drawFeature	Draw the feature.
drawGeometry	Used when looping (in redraw) over the features; draws the canvas.
drawExternalGraphic	Called to draw External graphics.
drawNamedSymbol	Called to draw Well Known Graphic Symbol Name.
setCanvasStyle	Prepare the canvas for drawing by setting various global settings.
featureIdToHex	Convert a feature ID string into an RGB hex string.
setHitContextStyle	Prepare the hit canvas for drawing by setting various global settings.
drawPoint	This method is only called by the renderer itself.
drawLineString	This method is only called by the renderer itself.
drawLinearRing	This method is only called by the renderer itself.
renderPath	Render a path with stroke and optional fill.
drawPolygon	This method is only called by the renderer itself.
drawText	This method is only called by the renderer itself.
getLocalXY	transform geographic xy into pixel xy
clear	Clear all vectors from the renderer.
getFeatureIdFromEvent	Returns a feature id from an event on the renderer.
eraseFeatures	This is called by the layer to erase features; removes the feature from the list, then redraws the layer.
redraw	The real ‘meat’ of the function: any time things have changed, redraw() can be called to loop over all the data and (you guessed it) redraw it.
Constants
OpenLayers.Renderer.Canvas.LABEL_ALIGN	{Object}
OpenLayers.Renderer.Canvas.LABEL_FACTOR	{Object}
OpenLayers.Renderer.Canvas.drawImageScaleFactor	{Number} Scale factor to apply to the canvas drawImage arguments.

Properties

hitDetection

{Boolean} Allow for hit detection of features. Default is true.

hitOverflow

{Number} The method for converting feature identifiers to color values supports 16777215 sequential values. Two features cannot be predictably detected if their identifiers differ by more than this value. The hitOverflow allows for bigger numbers (but the difference in values is still limited).

canvas

{Canvas} The canvas context object.

features

{Object} Internal object of feature/style pairs for use in redrawing the layer.

pendingRedraw

{Boolean} The renderer needs a redraw call to render features added while the renderer was locked.

cachedSymbolBounds

{Object} Internal cache of calculated symbol extents.

Constructor

OpenLayers.Renderer.Canvas

Parameters

containerID	{String}
options	{Object} Optional properties to be set on the renderer.

Functions

setExtent

setExtent: function()

Set the visible part of the layer.

Parameters

extent	{OpenLayers.Bounds}
resolutionChanged	{Boolean}

Returns

{Boolean} true to notify the layer that the new extent does not exceed the coordinate range, and the features will not need to be redrawn. False otherwise.

eraseGeometry

eraseGeometry: function( geometry,
featureId )

Erase a geometry from the renderer. Because the Canvas renderer has ‘memory’ of the features that it has drawn, we have to remove the feature so it doesn’t redraw.

Parameters

geometry	{OpenLayers.Geometry}
featureId	{String}

supported

supported: function()

Returns

{Boolean} Whether or not the browser supports the renderer class

setSize

setSize: function( size )

Sets the size of the drawing surface.

Once the size is updated, redraw the canvas.

Parameters

size	{OpenLayers.Size}

drawFeature

drawFeature: function( feature,
style )

Draw the feature. Stores the feature in the features list, then redraws the layer.

Parameters

feature	{OpenLayers.Feature.Vector}
style	{<Object>}

Returns

{Boolean} The feature has been drawn completely. If the feature has no geometry, undefined will be returned. If the feature is not rendered for other reasons, false will be returned.

drawGeometry

drawGeometry: function( geometry,
style,
featureId )

Used when looping (in redraw) over the features; draws the canvas.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}

drawExternalGraphic

drawExternalGraphic: function( geometry,
style,
featureId )

Called to draw External graphics.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

drawNamedSymbol

drawNamedSymbol: function( geometry,
style,
featureId )

Called to draw Well Known Graphic Symbol Name. This method is only called by the renderer itself.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

setCanvasStyle

setCanvasStyle: function( type,
style )

Prepare the canvas for drawing by setting various global settings.

Parameters

type	{String} one of ‘stroke’, ‘fill’, or ‘reset’
style	{Object} Symbolizer hash

featureIdToHex

featureIdToHex: function( featureId )

Convert a feature ID string into an RGB hex string.

Parameters

featureId

{String} Feature id

Returns

{String} RGB hex string.

setHitContextStyle

setHitContextStyle: function( type,
featureId,
symbolizer,
strokeScaling )

Prepare the hit canvas for drawing by setting various global settings.

Parameters

type	{String} one of ‘stroke’, ‘fill’, or ‘reset’
featureId	{String} The feature id.
symbolizer	{OpenLayers.Symbolizer} The symbolizer.

drawPoint

drawPoint: function( geometry,
style,
featureId )

This method is only called by the renderer itself.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

drawLineString

drawLineString: function( geometry,
style,
featureId )

This method is only called by the renderer itself.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

drawLinearRing

drawLinearRing: function( geometry,
style,
featureId )

This method is only called by the renderer itself.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

renderPath

renderPath: function( context,
geometry,
style,
featureId,
type )

Render a path with stroke and optional fill.

drawPolygon

drawPolygon: function( geometry,
style,
featureId )

This method is only called by the renderer itself.

Parameters

geometry	{OpenLayers.Geometry}
style	{Object}
featureId	{String}

drawText

drawText: function( location,
style )

This method is only called by the renderer itself.

Parameters

location	{<OpenLayers.Point>}
style	{Object}

getLocalXY

getLocalXY: function( point )

transform geographic xy into pixel xy

Parameters

point

{OpenLayers.Geometry.Point}

clear

clear: function()

Clear all vectors from the renderer.

getFeatureIdFromEvent

getFeatureIdFromEvent: function( evt )

Returns a feature id from an event on the renderer.

Parameters

evt	{OpenLayers.Event}

Returns

{<OpenLayers.Feature.Vector} A feature or undefined. This method returns a feature instead of a feature id to avoid an unnecessary lookup on the layer.

eraseFeatures

eraseFeatures: function( features )

This is called by the layer to erase features; removes the feature from the list, then redraws the layer.

Parameters

features

{Array(OpenLayers.Feature.Vector)}

redraw

redraw: function()

The real ‘meat’ of the function: any time things have changed, redraw() can be called to loop over all the data and (you guessed it) redraw it. Unlike Elements-based Renderers, we can’t interact with things once they’re drawn, to remove them, for example, so instead we have to just clear everything and draw from scratch.

Constants

OpenLayers.Renderer.Canvas.LABEL_ALIGN

{Object}

OpenLayers.Renderer.Canvas.LABEL_FACTOR

{Object}

OpenLayers.Renderer.Canvas.drawImageScaleFactor

{Number} Scale factor to apply to the canvas drawImage arguments. This is always 1 except for Android 2.1 devices, to work around http://code.google.com/p/android/issues/detail?id=5141.