[FEATURE] Preview of WMTS layers + add XYZ tile layers (PR #3473)

This introduces live preview when rendering WMTS layers - as soon as individual tiles are loaded, they are shown in map canvas... no need to wait with a blank map until all tiles are fully downloaded. Additionally, if there are already locally cached tiles of other zoom levels, they may be used in the preview while the tiles with best matching zoom level are being downloaded. This greatly improves the user experience when working with WMTS layers.

Additionally, I have added native support for XYZ tile layers into WMS provider (based on existing implementation of WMTS tiling). This allows loading of various new raster tile sources (e.g. OpenStreetMap tiles) that were before available only with QuickMapServices or OpenLayers plugins. To use XYZ tile layers, open the browser dock in QGIS and look for "Tile Servers (XYZ)" root entry. Right-clicking will open a menu to add connections. For example for OpenStreetMap the URL would be http://c.tile.openstreetmap.org/{z}/{x}/{y}.png

The work on WMTS live preview has been funded by Land Information New Zealand.

The work on XYZ tile layers has been funded by Lutra Consulting.

Author: wonder-sk

python/core/qgsmapsettings.sip

@@ -116,7 +116,8 @@ class QgsMapSettings
       UseRenderingOptimization,   //!< Enable vector simplification and other rendering optimizations
       DrawSelection,              //!< Whether vector selections should be shown in the rendered map
       DrawSymbolBounds,           //!< Draw bounds of symbols (for debugging/testing)
-      RenderMapTile               //!< Draw map such that there are no problems between adjacent tiles
+      RenderMapTile,              //!< Draw map such that there are no problems between adjacent tiles
+      RenderPartialOutput,        //!< Whether to make extra effort to update map image with partially rendered layers (better for interactive map canvas). Added in QGIS 3.0
     };
     typedef QFlags<QgsMapSettings::Flag> Flags;
 

python/core/qgsrendercontext.sip

@@ -23,6 +23,7 @@ class QgsRenderContext
       DrawSymbolBounds,         //!< Draw bounds of symbols (for debugging/testing)
       RenderMapTile,            //!< Draw map such that there are no problems between adjacent tiles
       Antialiasing,             //!< Use antialiasing while drawing
+      RenderPartialOutput,      //!< Whether to make extra effort to update map image with partially rendered layers (better for interactive map canvas). Added in QGIS 3.0
     };
     typedef QFlags<QgsRenderContext::Flag> Flags;
 

python/core/raster/qgsrasterinterface.sip

@@ -9,7 +9,30 @@ class QgsRasterBlockFeedback : QgsFeedback
 %TypeHeaderCode
 #include <qgsrasterinterface.h>
 %End
-    // TODO: extend with preview functionality??
+
+  public:
+    //! Construct a new raster block feedback object
+    QgsRasterBlockFeedback( QObject* parent = nullptr );
+
+    //! May be emitted by raster data provider to indicate that some partial data are available
+    //! and a new preview image may be produced
+    virtual void onNewData();
+
+    //! Whether the raster provider should return only data that are already available
+    //! without waiting for full result. By default this flag is not enabled.
+    //! @see setPreviewOnly()
+    bool isPreviewOnly() const;
+    //! set flag whether the block request is for preview purposes only
+    //! @see isPreviewOnly()
+    void setPreviewOnly( bool preview );
+
+    //! Whether our painter is drawing to a temporary image used just by this layer
+    //! @see setRenderPartialOutput()
+    bool renderPartialOutput() const;
+    //! Set whether our painter is drawing to a temporary image used just by this layer
+    //! @see renderPartialOutput()
+    void setRenderPartialOutput( bool enable );
+
 };
 
 
@@ -256,5 +279,10 @@ class QgsRasterInterface
                          int theStats = QgsRasterBandStats::All,
                          const QgsRectangle & theExtent = QgsRectangle(),
                          int theBinCount = 0 );
+
+  private:
+    QgsRasterInterface(const QgsRasterInterface &);
+    QgsRasterInterface &operator=(const QgsRasterInterface &);
+
 };
 

python/core/raster/qgsrasterprojector.sip

@@ -1,6 +1,10 @@
 
-/** Raster projector */
-
+/** \ingroup core
+ * \brief QgsRasterProjector implements approximate projection support for
+ * it calculates grid of points in source CRS for target CRS + extent
+ * which are used to calculate affine transformation matrices.
+ * \class QgsRasterProjector
+ */
 class QgsRasterProjector : QgsRasterInterface
 {
 %TypeHeaderCode
@@ -18,33 +22,6 @@ class QgsRasterProjector : QgsRasterInterface
       Exact,   //!< Exact, precise but slow
     };
 
-    /** \brief QgsRasterProjector implements approximate projection support for
-     * it calculates grid of points in source CRS for target CRS + extent
-     * which are used to calculate affine transformation matrices.
-     */
-
-    QgsRasterProjector( const QgsCoordinateReferenceSystem& theSrcCRS,
-                        const QgsCoordinateReferenceSystem& theDestCRS,
-                        int theSrcDatumTransform,
-                        int theDestDatumTransform,
-                        const QgsRectangle& theDestExtent,
-                        int theDestRows, int theDestCols,
-                        double theMaxSrcXRes, double theMaxSrcYRes,
-                        const QgsRectangle& theExtent
-                      );
-
-    QgsRasterProjector( const QgsCoordinateReferenceSystem& theSrcCRS,
-                        const QgsCoordinateReferenceSystem& theDestCRS,
-                        const QgsRectangle& theDestExtent,
-                        int theDestRows, int theDestCols,
-                        double theMaxSrcXRes, double theMaxSrcYRes,
-                        const QgsRectangle& theExtent
-                      );
-    QgsRasterProjector( const QgsCoordinateReferenceSystem& theSrcCRS,
-                        const QgsCoordinateReferenceSystem& theDestCRS,
-                        double theMaxSrcXRes, double theMaxSrcYRes,
-                        const QgsRectangle& theExtent
-                      );
     QgsRasterProjector();
 
     /** \brief The destructor */
@@ -66,9 +43,6 @@ class QgsRasterProjector : QgsRasterInterface
     /** \brief Get destination CRS */
     QgsCoordinateReferenceSystem destinationCrs() const;
 
-    /** \brief set maximum source resolution */
-    void setMaxSrcRes( double theMaxSrcXRes, double theMaxSrcYRes );
-
     Precision precision() const;
     void setPrecision( Precision precision );
     // Translated precision mode, for use in ComboBox etc.

src/app/qgslayerstylingwidget.cpp

@@ -38,6 +38,7 @@
 #include "qgsrenderer.h"
 #include "qgsrendererregistry.h"
 #include "qgsmaplayerregistry.h"
+#include "qgsrasterdataprovider.h"
 #include "qgsrasterlayer.h"
 #include "qgsmaplayerconfigwidget.h"
 #include "qgsmaplayerstylemanagerwidget.h"
@@ -171,10 +172,14 @@ void QgsLayerStylingWidget::setLayer( QgsMapLayer *layer )
     transparencyItem->setToolTip( tr( "Transparency" ) );
     transparencyItem->setData( Qt::UserRole, RasterTransparency );
     mOptionsListWidget->addItem( transparencyItem );
-    QListWidgetItem* histogramItem = new QListWidgetItem( QgsApplication::getThemeIcon( "propertyicons/histogram.png" ), QString() );
-    histogramItem->setData( Qt::UserRole, RasterHistogram );
-    mOptionsListWidget->addItem( histogramItem );
-    histogramItem->setToolTip( tr( "Histogram" ) );
+
+    if ( static_cast<QgsRasterLayer*>( layer )->dataProvider()->capabilities() & QgsRasterDataProvider::Size )
+    {
+      QListWidgetItem* histogramItem = new QListWidgetItem( QgsApplication::getThemeIcon( "propertyicons/histogram.png" ), QString() );
+      histogramItem->setData( Qt::UserRole, RasterHistogram );
+      mOptionsListWidget->addItem( histogramItem );
+      histogramItem->setToolTip( tr( "Histogram" ) );
+    }
   }
 
   Q_FOREACH ( QgsMapLayerConfigWidgetFactory* factory, mPageFactories )
@@ -392,21 +397,24 @@ void QgsLayerStylingWidget::updateCurrentWidgetLayer()
       }
       case 2: // Histogram
       {
-        if ( mRasterStyleWidget )
+        if ( rlayer->dataProvider()->capabilities() & QgsRasterDataProvider::Size )
         {
-          mRasterStyleWidget->deleteLater();
-          delete mRasterStyleWidget;
+          if ( mRasterStyleWidget )
+          {
+            mRasterStyleWidget->deleteLater();
+            delete mRasterStyleWidget;
+          }
+          mRasterStyleWidget = new QgsRendererRasterPropertiesWidget( rlayer, mMapCanvas, mWidgetStack );
+          mRasterStyleWidget->syncToLayer( rlayer );
+          connect( mRasterStyleWidget, SIGNAL( widgetChanged() ), this, SLOT( autoApply() ) );
+
+          QgsRasterHistogramWidget* widget = new QgsRasterHistogramWidget( rlayer, mWidgetStack );
+          connect( widget, SIGNAL( widgetChanged() ), this, SLOT( autoApply() ) );
+          QString name = mRasterStyleWidget->currentRenderWidget()->renderer()->type();
+          widget->setRendererWidget( name, mRasterStyleWidget->currentRenderWidget() );
+
+          mWidgetStack->addMainPanel( widget );
         }
-        mRasterStyleWidget = new QgsRendererRasterPropertiesWidget( rlayer, mMapCanvas, mWidgetStack );
-        mRasterStyleWidget->syncToLayer( rlayer );
-        connect( mRasterStyleWidget, SIGNAL( widgetChanged() ), this, SLOT( autoApply() ) );
-
-        QgsRasterHistogramWidget* widget = new QgsRasterHistogramWidget( rlayer, mWidgetStack );
-        connect( widget, SIGNAL( widgetChanged() ), this, SLOT( autoApply() ) );
-        QString name = mRasterStyleWidget->currentRenderWidget()->renderer()->type();
-        widget->setRendererWidget( name, mRasterStyleWidget->currentRenderWidget() );
-
-        mWidgetStack->addMainPanel( widget );
         break;
       }
       default:

src/core/qgsdataitemproviderregistry.cpp

@@ -21,6 +21,8 @@
 #include "qgslogger.h"
 #include "qgsproviderregistry.h"
 
+typedef QList<QgsDataItemProvider*> dataItemProviders_t();
+
 
 /**
  * \ingroup core
@@ -64,6 +66,17 @@ QgsDataItemProviderRegistry::QgsDataItemProviderRegistry()
     if ( !library )
       continue;
 
+    // new / better way of returning data items from providers
+
+    dataItemProviders_t* dataItemProvidersFn = reinterpret_cast< dataItemProviders_t * >( cast_to_fptr( library->resolve( "dataItemProviders" ) ) );
+    if ( dataItemProvidersFn )
+    {
+      // the function is a factory - we keep ownership of the returned providers
+      mProviders << dataItemProvidersFn();
+    }
+
+    // legacy support - using dataItem() and dataCapabilities() methods
+
     dataCapabilities_t * dataCapabilities = reinterpret_cast< dataCapabilities_t * >( cast_to_fptr( library->resolve( "dataCapabilities" ) ) );
     if ( !dataCapabilities )
     {

src/core/qgsmaplayer.cpp

@@ -234,7 +234,9 @@ bool QgsMapLayer::readLayerXml( const QDomElement& layerElement )
     // This is modified version of old QgsWmsProvider::parseUri
     // The new format has always params crs,format,layers,styles and that params
     // should not appear in old format url -> use them to identify version
-    if ( !mDataSource.contains( "crs=" ) && !mDataSource.contains( "format=" ) )
+    // XYZ tile layers do not need to contain crs,format params, but they have type=xyz
+    if ( !mDataSource.contains( "type=" ) &&
+         !mDataSource.contains( "crs=" ) && !mDataSource.contains( "format=" ) )
     {
       QgsDebugMsg( "Old WMS URI format detected -> converting to new format" );
       QgsDataSourceUri uri;

src/core/qgsmaprenderercustompainterjob.cpp

@@ -333,6 +333,12 @@ bool QgsMapRendererJob::needTemporaryImage( QgsMapLayer* ml )
       return true;
     }
   }
+  else if ( ml->type() == QgsMapLayer::RasterLayer )
+  {
+    // preview of intermediate raster rendering results requires a temporary output image
+    if ( mSettings.testFlag( QgsMapSettings::RenderPartialOutput ) )
+      return true;
+  }
 
   return false;
 }

src/core/qgsmapsettings.h

@@ -164,7 +164,8 @@ class CORE_EXPORT QgsMapSettings
       UseRenderingOptimization = 0x20,  //!< Enable vector simplification and other rendering optimizations
       DrawSelection            = 0x40,  //!< Whether vector selections should be shown in the rendered map
       DrawSymbolBounds         = 0x80,  //!< Draw bounds of symbols (for debugging/testing)
-      RenderMapTile            = 0x100  //!< Draw map such that there are no problems between adjacent tiles
+      RenderMapTile            = 0x100, //!< Draw map such that there are no problems between adjacent tiles
+      RenderPartialOutput      = 0x200, //!< Whether to make extra effort to update map image with partially rendered layers (better for interactive map canvas). Added in QGIS 3.0
       // TODO: ignore scale-based visibility (overview)
     };
     Q_DECLARE_FLAGS( Flags, Flag )

src/core/qgsrendercontext.cpp

@@ -129,6 +129,7 @@ QgsRenderContext QgsRenderContext::fromMapSettings( const QgsMapSettings& mapSet
   ctx.setFlag( DrawSymbolBounds, mapSettings.testFlag( QgsMapSettings::DrawSymbolBounds ) );
   ctx.setFlag( RenderMapTile, mapSettings.testFlag( QgsMapSettings::RenderMapTile ) );
   ctx.setFlag( Antialiasing, mapSettings.testFlag( QgsMapSettings::Antialiasing ) );
+  ctx.setFlag( RenderPartialOutput, mapSettings.testFlag( QgsMapSettings::RenderPartialOutput ) );
   ctx.setRasterScaleFactor( 1.0 );
   ctx.setScaleFactor( mapSettings.outputDpi() / 25.4 ); // = pixels per mm
   ctx.setRendererScale( mapSettings.scale() );

src/core/qgsrendercontext.h

@@ -65,6 +65,7 @@ class CORE_EXPORT QgsRenderContext
       DrawSymbolBounds         = 0x20,  //!< Draw bounds of symbols (for debugging/testing)
       RenderMapTile            = 0x40,  //!< Draw map such that there are no problems between adjacent tiles
       Antialiasing             = 0x80,  //!< Use antialiasing while drawing
+      RenderPartialOutput      = 0x100, //!< Whether to make extra effort to update map image with partially rendered layers (better for interactive map canvas). Added in QGIS 3.0
     };
     Q_DECLARE_FLAGS( Flags, Flag )
 

src/core/raster/qgsrasterdrawer.cpp

@@ -88,10 +88,20 @@ void QgsRasterDrawer::draw( QPainter* p, QgsRasterViewPort* viewPort, const QgsM
       }
     }
 
+    if ( feedback && feedback->renderPartialOutput() )
+    {
+      // there could have been partial preview written before
+      // so overwrite anything with the resulting image.
+      // (we are guaranteed to have a temporary image for this layer, see QgsMapRendererJob::needTemporaryImage)
+      p->setCompositionMode( QPainter::CompositionMode_Source );
+    }
+
     drawImage( p, viewPort, img, topLeftCol, topLeftRow, theQgsMapToPixel );
 
     delete block;
 
+    p->setCompositionMode( QPainter::CompositionMode_SourceOver );  // go back to the default composition mode
+
     // ok this does not matter much anyway as the tile size quite big so most of the time
     // there would be just one tile for the whole display area, but it won't hurt...
     if ( feedback && feedback->isCancelled() )

src/core/raster/qgsrasterinterface.h

@@ -36,7 +36,36 @@
  */
 class CORE_EXPORT QgsRasterBlockFeedback : public QgsFeedback
 {
-    // TODO: extend with preview functionality??
+  public:
+    //! Construct a new raster block feedback object
+    QgsRasterBlockFeedback( QObject* parent = nullptr ) : QgsFeedback( parent ), mPreviewOnly( false ), mRenderPartialOutput( false ) {}
+
+    //! May be emitted by raster data provider to indicate that some partial data are available
+    //! and a new preview image may be produced
+    virtual void onNewData() {}
+
+    //! Whether the raster provider should return only data that are already available
+    //! without waiting for full result. By default this flag is not enabled.
+    //! @see setPreviewOnly()
+    bool isPreviewOnly() const { return mPreviewOnly; }
+    //! set flag whether the block request is for preview purposes only
+    //! @see isPreviewOnly()
+    void setPreviewOnly( bool preview ) { mPreviewOnly = preview; }
+
+    //! Whether our painter is drawing to a temporary image used just by this layer
+    //! @see setRenderPartialOutput()
+    bool renderPartialOutput() const { return mRenderPartialOutput; }
+    //! Set whether our painter is drawing to a temporary image used just by this layer
+    //! @see renderPartialOutput()
+    void setRenderPartialOutput( bool enable ) { mRenderPartialOutput = enable; }
+
+  private:
+    //! Whether the raster provider should return only data that are already available
+    //! without waiting for full result
+    bool mPreviewOnly;
+
+    //! Whether our painter is drawing to a temporary image used just by this layer
+    bool mRenderPartialOutput;
 };
 
 
@@ -258,6 +287,9 @@ class CORE_EXPORT QgsRasterInterface
                          int theStats = QgsRasterBandStats::All,
                          const QgsRectangle & theExtent = QgsRectangle(),
                          int theBinCount = 0 );
+
+  private:
+    Q_DISABLE_COPY( QgsRasterInterface )   // there is clone() for copying
 };
 
 #endif

src/core/raster/qgsrasterlayerrenderer.cpp

@@ -29,7 +29,7 @@ QgsRasterLayerRenderer::QgsRasterLayerRenderer( QgsRasterLayer* layer, QgsRender
     , mRasterViewPort( nullptr )
     , mPipe( nullptr )
     , mContext( rendererContext )
-    , mFeedback( new QgsRasterBlockFeedback() )
+    , mFeedback( new Feedback( this ) )
 {
   mPainter = rendererContext.painter();
   const QgsMapToPixel& theQgsMapToPixel = rendererContext.mapToPixel();
@@ -226,3 +226,35 @@ QgsFeedback* QgsRasterLayerRenderer::feedback() const
 {
   return mFeedback;
 }
+
+QgsRasterLayerRenderer::Feedback::Feedback( QgsRasterLayerRenderer *r )
+    : mR( r )
+    , mMinimalPreviewInterval( 250 )
+{
+  setRenderPartialOutput( r->mContext.testFlag( QgsRenderContext::RenderPartialOutput ) );
+}
+
+void QgsRasterLayerRenderer::Feedback::onNewData()
+{
+  if ( !renderPartialOutput() )
+    return;  // we were not asked for partial renders and we may not have a temporary image for overwriting...
+
+  // update only once upon a time
+  // (preview itself takes some time)
+  if ( mLastPreview.isValid() && mLastPreview.msecsTo( QTime::currentTime() ) < mMinimalPreviewInterval )
+    return;
+
+  // TODO: update only the area that got new data
+
+  QgsDebugMsg( QString( "new raster preview! %1" ).arg( mLastPreview.msecsTo( QTime::currentTime() ) ) );
+  QTime t;
+  t.start();
+  QgsRasterBlockFeedback feedback;
+  feedback.setPreviewOnly( true );
+  feedback.setRenderPartialOutput( true );
+  QgsRasterIterator iterator( mR->mPipe->last() );
+  QgsRasterDrawer drawer( &iterator );
+  drawer.draw( mR->mPainter, mR->mRasterViewPort, mR->mMapToPixel, &feedback );
+  QgsDebugMsg( QString( "total raster preview time: %1 ms" ).arg( t.elapsed() ) );
+  mLastPreview = QTime::currentTime();
+}