diff --git a/python/core/raster/qgsrasterinterface.sip b/python/core/raster/qgsrasterinterface.sip
index b51a01336c8..5d935a9caf3 100644
--- a/python/core/raster/qgsrasterinterface.sip
+++ b/python/core/raster/qgsrasterinterface.sip
@@ -9,7 +9,21 @@ 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 );
+
+    //! whether the raster provider should return only data that are already available
+    //! without waiting for full result
+    bool preview_only;
+
+    //! whether our painter is drawing to a temporary image used just by this layer
+    bool render_partial_output;
+
+    //! 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();
 };
 
 
diff --git a/src/core/raster/qgsrasterinterface.h b/src/core/raster/qgsrasterinterface.h
index cdc8805022a..931b0ff8809 100644
--- a/src/core/raster/qgsrasterinterface.h
+++ b/src/core/raster/qgsrasterinterface.h
@@ -37,6 +37,7 @@
 class CORE_EXPORT QgsRasterBlockFeedback : public QgsFeedback
 {
   public:
+    //! construct a new raster block feedback object
     QgsRasterBlockFeedback( QObject* parent = nullptr ) : QgsFeedback( parent ), preview_only( false ), render_partial_output( false ) {}
 
     //! whether the raster provider should return only data that are already available
diff --git a/src/core/raster/qgsrasterlayerrenderer.cpp b/src/core/raster/qgsrasterlayerrenderer.cpp
index 33f6cbfd741..1a164330284 100644
--- a/src/core/raster/qgsrasterlayerrenderer.cpp
+++ b/src/core/raster/qgsrasterlayerrenderer.cpp
@@ -29,7 +29,7 @@ QgsRasterLayerRenderer::QgsRasterLayerRenderer( QgsRasterLayer* layer, QgsRender
     , mRasterViewPort( nullptr )
     , mPipe( nullptr )
     , mContext( rendererContext )
-    , mFeedback( new MyFeedback( this ) )
+    , mFeedback( new Feedback( this ) )
 {
   mPainter = rendererContext.painter();
   const QgsMapToPixel& theQgsMapToPixel = rendererContext.mapToPixel();
@@ -227,14 +227,14 @@ QgsFeedback* QgsRasterLayerRenderer::feedback() const
   return mFeedback;
 }
 
-MyFeedback::MyFeedback( QgsRasterLayerRenderer *r )
+QgsRasterLayerRenderer::Feedback::Feedback( QgsRasterLayerRenderer *r )
     : mR( r )
     , mMinimalPreviewInterval( 250 )
 {
   render_partial_output = r->mContext.testFlag( QgsRenderContext::RenderPartialOutput );
 }
 
-void MyFeedback::onNewData()
+void QgsRasterLayerRenderer::Feedback::onNewData()
 {
   qDebug( "\nGOT NEW DATA!\n" );
 
diff --git a/src/core/raster/qgsrasterlayerrenderer.h b/src/core/raster/qgsrasterlayerrenderer.h
index b4c30e3115b..70b9b4ca120 100644
--- a/src/core/raster/qgsrasterlayerrenderer.h
+++ b/src/core/raster/qgsrasterlayerrenderer.h
@@ -31,18 +31,6 @@ class QgsRasterLayerRenderer;
 
 #include "qgsrasterinterface.h"
 
-class MyFeedback : public QgsRasterBlockFeedback
-{
-  public:
-    explicit MyFeedback( QgsRasterLayerRenderer* r );
-
-    virtual void onNewData() override;
-  private:
-    QgsRasterLayerRenderer* mR;
-    int mMinimalPreviewInterval;  //!< in miliseconds
-    QTime mLastPreview;
-};
-
 
 /** \ingroup core
  * Implementation of threaded rendering for raster layers.
@@ -69,8 +57,22 @@ class QgsRasterLayerRenderer : public QgsMapLayerRenderer
     QgsRasterPipe* mPipe;
     QgsRenderContext& mContext;
 
-    MyFeedback* mFeedback;
-    friend class MyFeedback;
+    //! Specific feedback class to provide preview of raster layer rendering.
+    class Feedback : public QgsRasterBlockFeedback
+    {
+      public:
+        explicit Feedback( QgsRasterLayerRenderer* r );
+
+        //! when notified of new data in data provider it launches a preview draw of the raster
+        virtual void onNewData() override;
+      private:
+        QgsRasterLayerRenderer* mR;   //!< parent renderer instance
+        int mMinimalPreviewInterval;  //!< in miliseconds
+        QTime mLastPreview;           //!< when last preview has been generated
+    };
+
+    //! feedback class for cancellation and preview generation
+    Feedback* mFeedback;
 };