AW: [Qgis-developer] Rendering single layer from mapcanvas
ashjas
ashjas at gmail.com
Thu Jul 9 14:05:05 EDT 2009
Hi Marco,
My requirement is also similar to what this post asks...
There are some doubts about ur method...please see if u can find time to
answer these..
would I be able to use all the mapTools like selection,identification etc on
the layer that i need to update constantly
by using your method (apart the normal static layers..)??
and can i add this live layer on to the legend and also set its symbology
from the layer property dialog box?
and i have a doubt about what u said .."In this subclass you need to create
a QgsVectorLayer.." so u mean that this subclass should have a
QgsVectorlayer object (or as many as the need may be for live layers) on
which i keep adding the live objects...and within this subclass i call the
paint method which will draw the objects??
and i guess i have to keep the same reference to the only Qgsmapcanvas
object for this subclass aswell as the objects are to be drawn only on the
mainCanvas.. and what about maprenderer object??should it be also the same
object as for the main layers??
and about implementing the paint method.. in short i would be calling the
drawFeature of the QgsVectorLayer Class(for all the features on the layer )
from within the paint function that would be custom implemented.. is it?
Please enlighten me..
Thanks for finding time and helping us.. :)
Best Regards.
Ashish
Hugentobler Marco wrote:
>
> Hi Bonar
>
> QGIS renders the map into one image canvas item (QgsMapCanvasMap).
> Currently, it is not possible to refresh only one layer in this item.
> However, it is possible to render the content of the three layers that
> stay constant into a QgsMapCanvasMap (as you do now with all the four
> layers). For the layer that changes you could create a new canvas item (as
> a new subclass of QgsMapCanvasItem). In this subclass you need to create a
> QgsVectorLayer configured with your database instance . Then you could
> implement the paint method, there query all the features inside the view
> extent, use the transformation methods of QgsMapCanvasItem
> (toCanvasCoordinates()) and finally use QPainter to draw the objects as
> you want. Important is that the new item has the same size as the
> mapcanvas and also a transparent background such that you may see the
> content of the other three background layers.
>
> If then something in the datasource changes, you update your item class
> and only the item with one layer is repainted. The background with the
> three other layers stays the same.
>
>
> Regards,
> Marco
>
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: qgis-developer-bounces at lists.osgeo.org im Auftrag von bonar
> Gesendet: Mo 25.05.2009 11:41
> An: qgis-developer at lists.osgeo.org
> Betreff: [Qgis-developer] Rendering single layer from mapcanvas
>
>
> Hi guys, Tim & Dr.Marco
>
> I was tried to display real-time data in my mapcanvas. In my mapcanvas, i
> have 4 layer, but i juz want to refresh 1 layer only(this layer retrieve
> data from PostGis) from the mapcanvas without refreshing all layer in the
> mapcanvas. I already searching from this forum and Google it, and the
> result
> is i should use QgsMapCanvasItem that have that capabilities to rendering
> single layer without refreshing mapcanvas. But, i don't know how to
> implement it in my application. I'm using sample application from Mr.Tim
> Sutton, it is a great tutorial for a beginner like me, and i think its
> better to include the code in here. This is what i already done:
>
>
> //Setting my layer
>
> mpMapCanvas= new QgsMapCanvas(0, 0);
> mpMapCanvas->enableAntiAliasing(true);
> mpMapCanvas->useImageToRender(true);
> mpMapCanvas->setCanvasColor(QColor(255, 255, 255));
> mpMapCanvas->freeze(false);
> mpMapCanvas->setVisible(true);
>
> QString myLayerPathNegeri = LAYERPATH() + "klkv_state.shp";
> QString myLayerBaseNameNegeri = "klkv_state";
> QString myProviderName = "ogr";
>
> QString myLayerPathDistrict = LAYERPATH() + "klkv_district.shp";
> QString myLayerBaseNameDistrict = "klkv_district";
>
> QString myLayerPathMukim = LAYERPATH() + "klkv_mukim.shp";
> QString myLayerBaseNameMukim = "klkv_mukim";
>
> QString myLayerPathPoi = "location_poi";
> QString myLayerBaseNamePoi = "location_poi";
>
> QgsVectorLayer * mypLayerNegeri = new QgsVectorLayer(myLayerPathNegeri,
> myLayerBaseNameNegeri, myProviderName);
>
> QgsVectorLayer * mypLayerDistrict = new
> QgsVectorLayer(myLayerPathDistrict, myLayerBaseNameDistrict,
> myProviderName);
>
> QgsVectorLayer * mypLayerMukim = new QgsVectorLayer(myLayerPathMukim,
> myLayerBaseNameMukim, myProviderName);
>
> QgsVectorLayer * mypLayerPoi = new
> QgsVectorLayer(POSTGIS_LAYER_SETUP_INCIDENT_POI_FUNC(),
> myLayerBaseNamePoi,
> "postgres");
>
>
> QgsSingleSymbolRenderer *mypRendererNegeri = new
> QgsSingleSymbolRenderer(mypLayerNegeri->geometryType());
> QList<QgsMapCanvasLayer> myLayerSet;
> mypLayerNegeri->setRenderer(mypRendererNegeri);
>
> QgsSingleSymbolRenderer *mypRendererDistrict = new
> QgsSingleSymbolRenderer(mypLayerDistrict->geometryType());
> mypLayerDistrict->setRenderer(mypRendererDistrict);
>
> QgsSingleSymbolRenderer *mypRendererMukim = new
> QgsSingleSymbolRenderer(mypLayerMukim->geometryType());
> mypLayerMukim->setRenderer(mypRendererMukim);
>
>
> QgsSingleSymbolRenderer *mypRendererPoi = new
> QgsSingleSymbolRenderer(mypLayerPoi->geometryType());
> mypLayerPoi->setRenderer(mypRendererPoi);
>
>
> QgsMapLayerRegistry::instance()->addMapLayer(mypLayerNegeri, TRUE);
> QgsMapLayerRegistry::instance()->addMapLayer(mypLayerDistrict, TRUE);
> QgsMapLayerRegistry::instance()->addMapLayer(mypLayerMukim, TRUE);
> QgsMapLayerRegistry::instance()->addMapLayer(mypLayerPoi, TRUE);
>
> myLayerSet.append(QgsMapCanvasLayer(mypLayerPoi));
> myLayerSet.append(QgsMapCanvasLayer(mypLayerMukim));
> myLayerSet.append(QgsMapCanvasLayer(mypLayerDistrict));
> myLayerSet.append(QgsMapCanvasLayer(mypLayerNegeri));
>
> mpMapCanvas->setLayerSet(myLayerSet);
>
>
> //I make a Qtimer to check if any update position for mypLayerPoi from
> updatingLocationPoiLayer() function
>
> QTimer *timerPoiRenderer = new QTimer(this);
> connect(timerPoiRenderer, SIGNAL(timeout()), this,
> SLOT(updatingLocationPoiLayer()));
> timerPoiRenderer->start(10 * 1000);// 10 seconds
>
>
> //this is how i tried to using QgsMapCanvasItem, sorry for the code
> because
> i am beginner for this QGis, so i juz try to play-around with the
> QgsMapCanvasItem code .
>
> void MyMain::updatingLocationPoiLayer()
> {
>
> QGraphicsScene *mScene = new QGraphicsScene();
> QgsMapCanvasMap* mMap = new QgsMapCanvasMap(mpMapCanvas);
> mScene->addItem( mMap );
> mScene->update();
> QList<QGraphicsItem*> list = mScene->items();
> QList<QGraphicsItem*>::iterator it = list.begin();
>
> while ( it != list.end() ){
> QgsMapCanvasItem* item = dynamic_cast<QgsMapCanvasItem*>( *it );
>
> if(item){
> item->updatePosition();
> QMessageBox::information( this, tr( "TEST" ), tr(
> "Update
> rendering" ) );
> }else{
> //it will goes here.
> QMessageBox::information( this, tr( "TEST" ), tr( "NOT
> Update rendering" ) );
> }
>
> it++;
> }
> }
>
> from my reading,what i understand is i should use
> QgsMapCanvasItem::updatePosition() to make my mapcanvas look like
> real-time.
> Is it true? And i really hope you guys can teach me about how to implement
> it in my code.
>
>
> Thanks in advance,
> Bonar
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