QGIS API Documentation  2.5.0-Master
 All Classes Namespaces Files Functions Variables Typedefs Enumerations Enumerator Friends Macros Modules Pages
Public Member Functions | Protected Attributes | List of all members
QgsMapLayerRenderer Class Referenceabstract

Base class for utility classes that encapsulate information necessary for rendering of map layers. More...

#include <qgsmaplayerrenderer.h>

Inheritance diagram for QgsMapLayerRenderer:
Inheritance graph
[legend]

Public Member Functions

 QgsMapLayerRenderer (const QString &layerID)
 
virtual ~QgsMapLayerRenderer ()
 
virtual bool render ()=0
 Do the rendering (based on data stored in the class) More...
 
QStringList errors () const
 Return list of errors (problems) that happened during the rendering. More...
 
QString layerID () const
 Get access to the ID of the layer rendered by this class. More...
 

Protected Attributes

QStringList mErrors
 
QString mLayerID
 

Detailed Description

Base class for utility classes that encapsulate information necessary for rendering of map layers.

The rendering is typically done in a background thread, so it is necessary to keep all structures required for rendering away from the original map layer because it may change any time.

Because the data needs to be copied (to avoid the need for locking), is is highly desirable to use copy-on-write where possible. This way, the overhead of copying (both memory and CPU) will be kept low. Qt containers and various Qt classes use implicit sharing.

The scenario will be:

  1. renderer job (doing preparation in the GUI thread) calls QgsMapLayer::createMapRenderer() and gets instance of this class. The instance is initialized at that point and should not need additional calls to QgsVectorLayer.
  2. renderer job (still in GUI thread) stores the renderer for later use.
  3. renderer job (in worker thread) calls QgsMapLayerRenderer::render()
  4. renderer job (again in GUI thread) will check errors() and report them
Note
added in 2.4

Constructor & Destructor Documentation

QgsMapLayerRenderer::QgsMapLayerRenderer ( const QString &  layerID)
inline
virtual QgsMapLayerRenderer::~QgsMapLayerRenderer ( )
inlinevirtual

Member Function Documentation

QStringList QgsMapLayerRenderer::errors ( ) const
inline

Return list of errors (problems) that happened during the rendering.

QString QgsMapLayerRenderer::layerID ( ) const
inline

Get access to the ID of the layer rendered by this class.

virtual bool QgsMapLayerRenderer::render ( )
pure virtual

Do the rendering (based on data stored in the class)

Implemented in QgsVectorLayerRenderer, QgsPluginLayerRenderer, and QgsRasterLayerRenderer.

Member Data Documentation

QStringList QgsMapLayerRenderer::mErrors
protected
QString QgsMapLayerRenderer::mLayerID
protected

The documentation for this class was generated from the following file: