From 381c8819fa4f10d210cc48ed502652a12776649e Mon Sep 17 00:00:00 2001
From: Mathieu Pellerin <nirvn.asia@gmail.com>
Date: Tue, 30 Jan 2024 14:10:11 +0700
Subject: [PATCH] [layouts] Fix rendering of map preview on high DPI screens

---
 src/core/layout/qgslayoutitemmap.cpp | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/core/layout/qgslayoutitemmap.cpp b/src/core/layout/qgslayoutitemmap.cpp
index 16314c597342..55527059157d 100644
--- a/src/core/layout/qgslayoutitemmap.cpp
+++ b/src/core/layout/qgslayoutitemmap.cpp
@@ -40,7 +40,9 @@
 #include "qgsvectortileutils.h"
 #include "qgsunittypes.h"
 
+#include <QApplication>
 #include <QPainter>
+#include <QScreen>
 #include <QStyleOptionGraphicsItem>
 #include <QTimer>
 
@@ -1112,7 +1114,7 @@ void QgsLayoutItemMap::paint( QPainter *painter, const QStyleOptionGraphicsItem
       //Background color is already included in cached image, so no need to draw
 
       double imagePixelWidth = mCacheFinalImage->width(); //how many pixels of the image are for the map extent?
-      double scale = rect().width() / imagePixelWidth;
+      double scale = rect().width() / imagePixelWidth * mCacheFinalImage->devicePixelRatio();
 
       QgsScopedQPainterState rotatedPainterState( painter );
 
@@ -1592,11 +1594,18 @@ void QgsLayoutItemMap::recreateCachedImageInBackground()
   if ( w <= 0 || h <= 0 )
     return;
 
-  mCacheRenderingImage.reset( new QImage( w, h, QImage::Format_ARGB32 ) );
+  double devicePixelRatio = 1.0;
+  if ( QWidget *activeWindow = QApplication::activeWindow() )
+  {
+    devicePixelRatio = ( activeWindow->screen() ? QApplication::activeWindow()->screen()->devicePixelRatio() : 1.0 );
+  }
+
+  mCacheRenderingImage.reset( new QImage( w * devicePixelRatio, h * devicePixelRatio, QImage::Format_ARGB32 ) );
 
   // set DPI of the image
   mCacheRenderingImage->setDotsPerMeterX( static_cast< int >( std::round( 1000 * w / widthLayoutUnits ) ) );
   mCacheRenderingImage->setDotsPerMeterY( static_cast< int >( std::round( 1000 * h / heightLayoutUnits ) ) );
+  mCacheRenderingImage->setDevicePixelRatio( devicePixelRatio );
 
   //start with empty fill to avoid artifacts
   mCacheRenderingImage->fill( QColor( 255, 255, 255, 0 ).rgba() );
@@ -1667,7 +1676,15 @@ QgsMapSettings QgsLayoutItemMap::mapSettings( const QgsRectangle &extent, QSizeF
   jobMapSettings.setOutputSize( size.toSize() );
   jobMapSettings.setOutputDpi( dpi );
   if ( layout()->renderContext().isPreviewRender() )
+  {
     jobMapSettings.setDpiTarget( layout()->renderContext().dpi() );
+    double devicePixelRatio = 1.0;
+    if ( QWidget *activeWindow = QApplication::activeWindow() )
+    {
+      devicePixelRatio = ( activeWindow->screen() ? QApplication::activeWindow()->screen()->devicePixelRatio() : 1.0 );
+    }
+    jobMapSettings.setDevicePixelRatio( devicePixelRatio );
+  }
   jobMapSettings.setBackgroundColor( Qt::transparent );
   jobMapSettings.setRotation( mEvaluatedMapRotation );
   if ( mLayout )