From b444c012b99b19de5bd5ee3d57388a0343f9f1af Mon Sep 17 00:00:00 2001
From: Jean Felder <jean.felder@oslandia.com>
Date: Sat, 9 Nov 2024 10:53:05 +0100
Subject: [PATCH] qgisapp: Update raster layer style when render details have
 changed

`QgsRasterLayer` updates the GUI (the renderer widget and the legend)
when the rendered values are updated. This does not work when multiple
canvas are displayed because each canvas causes a renderer update.

This issue is fixed by removing the GUI update from the raster layer
code. With this change, when the rendered values are updated, these
statistics are propagated to the canvas by the use of a
`QgsRenderedItemDetails`: `QgsRenderedCalculatedResults`. Then, only
the main canvas is notified of this change and updates the GUI
accordingly.
---
 src/app/qgisapp.cpp                | 38 ++++++++++++++++++++++++++++++
 src/app/qgisapp.h                  |  2 ++
 src/core/raster/qgsrasterlayer.cpp |  5 ----
 3 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/src/app/qgisapp.cpp b/src/app/qgisapp.cpp
index a4a5d942c682..149b8c05cd25 100644
--- a/src/app/qgisapp.cpp
+++ b/src/app/qgisapp.cpp
@@ -446,6 +446,8 @@
 #include "devtools/querylogger/qgsappquerylogger.h"
 #include "devtools/querylogger/qgsqueryloggerwidgetfactory.h"
 #include "devtools/profiler/qgsprofilerwidgetfactory.h"
+#include "qgsrendereditemresults.h"
+#include "qgsrenderedcalculatedresults.h"
 
 #include "browser/qgsinbuiltdataitemproviders.h"
 
@@ -1071,6 +1073,7 @@ QgisApp::QgisApp( QSplashScreen *splash, bool restorePlugins, bool skipBadLayers
   mMapCanvas = new QgsMapCanvas( centralWidget );
   mMapCanvas->setObjectName( QStringLiteral( "theMapCanvas" ) );
   mMapCanvas->setFlags( Qgis::MapCanvasFlag::ShowMainAnnotationLayer );
+  connect( mMapCanvas, &QgsMapCanvas::calculatedRenderDetailsChanged, this, &QgisApp::onCalculatedRenderDetailsChanged );
 
   // before anything, let's freeze canvas redraws
   QgsCanvasRefreshBlocker refreshBlocker;
@@ -17588,3 +17591,38 @@ void QgisApp::showEvent( QShowEvent *event )
     }
   } );
 }
+
+void QgisApp::onCalculatedRenderDetailsChanged()
+{
+  const QgsRenderedItemResults *renderedItemResults = mMapCanvas->renderedItemResults( false );
+  if ( !renderedItemResults )
+  {
+    return;
+  }
+
+  const QList<QgsRenderedItemDetails *> items = renderedItemResults->renderedItems();
+  QList<QString> computedLayerIds;
+  for ( const QgsRenderedItemDetails *item : renderedItemResults->renderedItems() )
+  {
+    if ( const QgsRenderedCalculatedResults *calculatedResults = dynamic_cast< const QgsRenderedCalculatedResults *>( item ) )
+    {
+      computedLayerIds.append( calculatedResults->layerId() );
+    }
+  }
+
+  if ( !computedLayerIds.empty() )
+  {
+    for ( QgsMapLayer *layer : mMapCanvas->layers() )
+    {
+      // refresh the legend and style of the raster layer
+      if ( QgsRasterLayer *rasterLayer = qobject_cast<QgsRasterLayer *>( layer ) )
+      {
+        if ( computedLayerIds.contains( rasterLayer->id() ) )
+        {
+          rasterLayer->emitStyleChanged();
+          emit rasterLayer->rendererChanged();
+        }
+      }
+    }
+  }
+}
diff --git a/src/app/qgisapp.h b/src/app/qgisapp.h
index 7514bb96ccde..ce3323bd985b 100644
--- a/src/app/qgisapp.h
+++ b/src/app/qgisapp.h
@@ -1445,6 +1445,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
 
     void onSnappingConfigChanged();
 
+    void onCalculatedRenderDetailsChanged();
+
     /**
      * Triggers validation of the specified \a crs.
      */
diff --git a/src/core/raster/qgsrasterlayer.cpp b/src/core/raster/qgsrasterlayer.cpp
index 04f70f668ed2..bc518636fc0f 100644
--- a/src/core/raster/qgsrasterlayer.cpp
+++ b/src/core/raster/qgsrasterlayer.cpp
@@ -1613,9 +1613,6 @@ bool QgsRasterLayer::refreshRenderer( QgsRasterRenderer *rasterRenderer, const Q
         }
       }
 
-      emit repaintRequested();
-      emitStyleChanged();
-      emit rendererChanged();
       return true;
     }
 
@@ -1650,8 +1647,6 @@ bool QgsRasterLayer::refreshRenderer( QgsRasterRenderer *rasterRenderer, const Q
         }
       }
 
-      emitStyleChanged();
-      emit rendererChanged();
       refreshed = true;
     }
   }