qgsrasterlayerrenderer: Change the logic to refresh the renderers

This replaces the existing logic in `QgsRasterLayerRenderer` which
calls `QgsRasterLayer::refreshRendererIfNeeded()` to refresh the
renderer associated `QgsRasterLayerRenderer` and the raster associated
with `QgsRasterLayer`. It also makes GUI updates.

With this approach, the following new logic is done:
 1. `QgsRasterRenderer::needsRefresh()` is called to check if
 `rasterRenderer` needs to be updated.
 2. If a refresh is needed, the new min/max values are computed by
 calling `QgsRasterLayer::computeMinMax()`
 3. The min/max values are used to refresh `rasterRenderer`
 4. The min/max values are stored in a `QgsRenderedLayerStatistics`
 and propagated to `QgisApp`
 5. In QgisApp, `QgsRenderedLayerStatistics` is used to refresh the
 renderer of `QgsRasterLayer` and force a refresh of the style and the
 legend if the change comes from the main canvas.

src/app/qgisapp.cpp

@@ -378,8 +378,11 @@
 #include "qgsbrightnesscontrastfilter.h"
 #include "qgsrasterlayersaveasdialog.h"
 #include "qgsrasterprojector.h"
+#include "qgsrasterrenderer.h"
 #include "qgsreadwritecontext.h"
 #include "qgsrectangle.h"
+#include "qgsrendereditemresults.h"
+#include "qgsrenderedlayerstatistics.h"
 #include "qgsreport.h"
 #include "qgsscalevisibilitydialog.h"
 #include "qgsgroupwmsdatadialog.h"
@@ -5212,12 +5215,19 @@ void QgisApp::createDecorations()
   addDecorationItem( decorationScaleBar );
   addDecorationItem( decorationLayoutExtent );
 
-  connect( mMapCanvas, &QgsMapCanvas::renderComplete, this, &QgisApp::renderDecorationItems );
+  connect( mMapCanvas, &QgsMapCanvas::renderComplete, this, &QgisApp::onRenderComplete );
   connect( this, &QgisApp::newProject, this, &QgisApp::projectReadDecorationItems );
   connect( this, &QgisApp::projectRead, this, &QgisApp::projectReadDecorationItems );
 }
 
-void QgisApp::renderDecorationItems( QPainter *p )
+void QgisApp::onRenderComplete( QPainter *p )
+{
+  renderDecorationItems( p );
+  handleRenderedLayerStatistics();
+}
+
+
+void QgisApp::renderDecorationItems( QPainter *p ) const
 {
   QgsRenderContext context = QgsRenderContext::fromMapSettings( mMapCanvas->mapSettings() );
   context.setPainter( p );
@@ -17581,3 +17591,27 @@ void QgisApp::showEvent( QShowEvent *event )
     }
   } );
 }
+
+void QgisApp::handleRenderedLayerStatistics() const
+{
+  const QgsRenderedItemResults *renderedItemResults = mMapCanvas->renderedItemResults( false );
+  if ( !renderedItemResults )
+  {
+    return;
+  }
+
+  for ( const QgsRenderedItemDetails *item : renderedItemResults->renderedItems() )
+  {
+    if ( const QgsRenderedLayerStatistics *layerStatistics = dynamic_cast< const QgsRenderedLayerStatistics *>( item ) )
+    {
+      QgsRasterLayer *rasterLayer = qobject_cast<QgsRasterLayer *>( QgsProject::instance()->mapLayer( layerStatistics->layerId() ) );
+      if ( rasterLayer )
+      {
+        // refresh the renderer of the layer, the style and the legend of the main canvas
+        rasterLayer->renderer()->refresh( layerStatistics->boundingBox(), layerStatistics->minimum(), layerStatistics->maximum() );
+        rasterLayer->emitStyleChanged();
+        emit rasterLayer->rendererChanged();
+      }
+    }
+  }
+}

src/app/qgisapp.h

@@ -2050,7 +2050,7 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     //! Activates label property tool
     void changeLabelProperties();
 
-    void renderDecorationItems( QPainter *p );
+    void onRenderComplete( QPainter *p );
     void projectReadDecorationItems();
 
     //! clear out any stuff from project
@@ -2430,6 +2430,10 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
      */
     QList< QgsMapToolCapture * > captureTools();
 
+    void renderDecorationItems( QPainter *p ) const;
+
+    void handleRenderedLayerStatistics() const;
+
     QgsScreenHelper *mScreenHelper = nullptr;
 
     QgisAppStyleSheet *mStyleSheetBuilder = nullptr;

src/core/raster/qgsrasterlayer.cpp

@@ -1695,7 +1695,21 @@ bool QgsRasterLayer::setSubsetString( const QString &subset )
   if ( res )
   {
     setExtent( mDataProvider->extent() );
-    refreshRenderer( renderer(), extent() );
+    QList<double> minValues;
+    QList<double> maxValues;
+    const QgsRasterMinMaxOrigin &minMaxOrigin = renderer()->minMaxOrigin();
+    for ( const int bandIdx : renderer()->usesBands() )
+    {
+      double min;
+      double max;
+
+      computeMinMax( bandIdx, minMaxOrigin, minMaxOrigin.limits(),
+                     extent(), static_cast<int>( QgsRasterLayer::SAMPLE_SIZE ),
+                     min, max );
+      minValues.append( min );
+      maxValues.append( max );
+    }
+    renderer()->refresh( extent(), minValues, maxValues, true );
     emit subsetStringChanged();
   }
 

src/core/raster/qgsrasterlayerrenderer.cpp

@@ -39,6 +39,7 @@
 #include "qgsinterval.h"
 #include "qgsunittypes.h"
 #include "qgsrasternuller.h"
+#include "qgsrenderedlayerstatistics.h"
 
 #include <QElapsedTimer>
 #include <QPointer>
@@ -273,7 +274,27 @@ QgsRasterLayerRenderer::QgsRasterLayerRenderer( QgsRasterLayer *layer, QgsRender
        && !( rendererContext.flags() & Qgis::RenderContextFlag::RenderPreviewJob )
        && !( rendererContext.flags() & Qgis::RenderContextFlag::Render3DMap ) )
   {
-    layer->refreshRendererIfNeeded( rasterRenderer, rendererContext.extent() );
+    if ( rasterRenderer->needsRefresh( rendererContext.extent() ) )
+    {
+      QList<double> minValues;
+      QList<double> maxValues;
+      const QgsRasterMinMaxOrigin &minMaxOrigin = rasterRenderer->minMaxOrigin();
+      for ( const int bandIdx : rasterRenderer->usesBands() )
+      {
+        double min;
+        double max;
+        layer->computeMinMax( bandIdx, minMaxOrigin, minMaxOrigin.limits(),
+                              rendererContext.extent(), static_cast<int>( QgsRasterLayer::SAMPLE_SIZE ),
+                              min, max );
+        minValues.append( min );
+        maxValues.append( max );
+      }
+
+      rasterRenderer->refresh( rendererContext.extent(), minValues, maxValues );
+      QgsRenderedLayerStatistics *layerStatistics = new QgsRenderedLayerStatistics( layer->id(), minValues, maxValues );
+      layerStatistics->setBoundingBox( rendererContext.extent() );
+      appendRenderedItemDetails( layerStatistics );
+    }
   }
 
   mPipe->evaluateDataDefinedProperties( rendererContext.expressionContext() );

src/gui/qgsmapcanvas.cpp

@@ -952,7 +952,7 @@ void QgsMapCanvas::rendererJobFinished()
 
     QImage img = mJob->renderedImage();
 
-    // emit renderComplete to get our decorations drawn
+    // emit renderComplete to get our decorations drawn and to handle computed statistics
     QPainter p( &img );
     emit renderComplete( &p );