[layouts][FEATURE] Don't force the whole layout to be rasterized

when exporting to PDF

If an individual layout item needs rasterisation in order to
be exported correctly, it can now be individually rasterised
without forcing every other item to also be rasterised.

This allows exports to PDF keeping as much as possible as vectors,
e.g. a map with layer opacity won't force labels, scalebars, etc
to be rasterised too.

To accompany this, a new "Always export as vectors" checkbox
was added to layout properties. If checked, this will force
the export to keep items as vectors, even when it causes the
output to look different to layouts.

Fixes #7885

python/core/layout/qgslayoutcontext.sip

@@ -27,6 +27,7 @@ class QgsLayoutContext : QObject
       FlagOutlineOnly,
       FlagAntialiasing,
       FlagUseAdvancedEffects,
+      FlagForceVectorOutput,
     };
     typedef QFlags<QgsLayoutContext::Flag> Flags;
 

python/core/layout/qgslayoutexporter.sip

@@ -212,7 +212,18 @@ Resolution to export layout at. If dpi <= 0 the default layout dpi will be used.
 
       bool rasterizeWholeImage;
 %Docstring
-Set to true to force whole layout to be rasterized while exporting
+ Set to true to force whole layout to be rasterized while exporting.
+
+ This option is mutually exclusive with forceVectorOutput.
+%End
+
+      bool forceVectorOutput;
+%Docstring
+ Set to true to force vector object exports, even when the resultant appearance will differ
+ from the layout. If false, some items may be rasterized in order to maintain their
+ correct appearance in the output.
+
+ This option is mutually exclusive with rasterizeWholeImage.
 %End
 
       QgsLayoutContext::Flags flags;

python/core/layout/qgslayoutitem.sip

@@ -827,6 +827,16 @@ Sets whether the item should be excluded from composer exports and prints.
 
  Subclasses should ensure that implemented overrides of this method
  also check the base class result.
+
+.. seealso:: :py:func:`requiresRasterization()`
+ :rtype: bool
+%End
+
+    virtual bool requiresRasterization() const;
+%Docstring
+ Returns true if the item is drawn in such a way that forces the whole layout
+ to be rasterised when exporting to vector formats.
+.. seealso:: :py:func:`containsAdvancedEffects()`
  :rtype: bool
 %End
 

python/core/layout/qgslayoutitempicture.sip

@@ -296,6 +296,8 @@ Forces a recalculation of the picture's frame size
 
     virtual void refreshDataDefinedProperty( const QgsLayoutObject::DataDefinedProperty property = QgsLayoutObject::AllProperties );
 
+    virtual bool containsAdvancedEffects() const;
+
 
   signals:
     void pictureRotationChanged( double newRotation );

src/app/layout/qgslayoutdesignerdialog.cpp

@@ -1552,9 +1552,14 @@ void QgsLayoutDesignerDialog::exportToPdf()
     showWmsPrintingWarning();
   }
 
-  if ( containsAdvancedEffects() )
+  if ( requiresRasterization() )
   {
-    showAdvancedEffectsWarning();
+    showRasterizationWarning();
+  }
+
+  if ( containsAdvancedEffects() && ( mLayout->customProperty( QStringLiteral( "forceVector" ), false ).toBool() ) )
+  {
+    showForceVectorWarning();
   }
 
   QgsSettings settings;
@@ -1602,7 +1607,8 @@ void QgsLayoutDesignerDialog::exportToPdf()
   QApplication::setOverrideCursor( Qt::BusyCursor );
 
   QgsLayoutExporter::PdfExportSettings pdfSettings;
-  pdfSettings.rasteriseWholeImage = mLayout->customProperty( QStringLiteral( "rasterise" ), false ).toBool();
+  pdfSettings.rasterizeWholeImage = mLayout->customProperty( QStringLiteral( "rasterise" ), false ).toBool();
+  pdfSettings.forceVectorOutput = mLayout->customProperty( QStringLiteral( "forceVector" ), false ).toBool();
 
   QgsLayoutExporter exporter( mLayout );
   switch ( exporter.exportToPdf( outputFileName, pdfSettings ) )
@@ -1783,6 +1789,19 @@ void QgsLayoutDesignerDialog::showWmsPrintingWarning()
   }
 }
 
+bool QgsLayoutDesignerDialog::requiresRasterization() const
+{
+  QList< QgsLayoutItem *> items;
+  mLayout->layoutItems( items );
+
+  for ( QgsLayoutItem *currentItem : qgis::as_const( items ) )
+  {
+    if ( currentItem->requiresRasterization() )
+      return true;
+  }
+  return false;
+}
+
 bool QgsLayoutDesignerDialog::containsAdvancedEffects() const
 {
   QList< QgsLayoutItem *> items;
@@ -1796,10 +1815,11 @@ bool QgsLayoutDesignerDialog::containsAdvancedEffects() const
   return false;
 }
 
-void QgsLayoutDesignerDialog::showAdvancedEffectsWarning()
+void QgsLayoutDesignerDialog::showRasterizationWarning()
 {
-  bool rasterize = mLayout->customProperty( QStringLiteral( "rasterise" ), false ).toBool();
-  if ( rasterise )
+
+  if ( mLayout->customProperty( QStringLiteral( "rasterise" ), false ).toBool() ||
+       mLayout->customProperty( QStringLiteral( "forceVector" ), false ).toBool() )
     return;
 
   QgsMessageViewer *m = new QgsMessageViewer( this, QgsGuiUtils::ModalDialogFlags, false );
@@ -1817,6 +1837,27 @@ void QgsLayoutDesignerDialog::showAdvancedEffectsWarning()
   delete m;
 }
 
+void QgsLayoutDesignerDialog::showForceVectorWarning()
+{
+  QgsSettings settings;
+  if ( settings.value( QStringLiteral( "LayoutDesigner/hideForceVectorWarning" ), false, QgsSettings::App ).toBool() )
+    return;
+
+  QgsMessageViewer *m = new QgsMessageViewer( this, QgsGuiUtils::ModalDialogFlags, false );
+  m->setWindowTitle( tr( "Force Vector" ) );
+  m->setMessage( tr( "This layout has the \"Always export as vectors\" option enabled, but the layout contains effects such as blend modes or vector layer transparency, which cannot be printed as vectors. The generated file will differ from the layout contents." ), QgsMessageOutput::MessageText );
+  m->setCheckBoxText( tr( "Never show this message again" ) );
+  m->setCheckBoxState( Qt::Unchecked );
+  m->setCheckBoxVisible( true );
+  m->showMessage( true );
+
+  if ( m->checkBoxState() == Qt::Checked )
+  {
+    settings.setValue( QStringLiteral( "LayoutDesigner/hideForceVectorWarning" ), true, QgsSettings::App );
+  }
+  delete m;
+}
+
 void QgsLayoutDesignerDialog::selectItems( const QList<QgsLayoutItem *> items )
 {
   for ( QGraphicsItem *item : items )

src/app/layout/qgslayoutdesignerdialog.h

@@ -371,10 +371,13 @@ class QgsLayoutDesignerDialog: public QMainWindow, private Ui::QgsLayoutDesigner
     void showWmsPrintingWarning();
 
     //! True if the layout contains advanced effects, such as blend modes
+    bool requiresRasterization() const;
+
     bool containsAdvancedEffects() const;
 
     //! Displays a warning because of incompatibility between blend modes and QPrinter
-    void showAdvancedEffectsWarning();
+    void showRasterizationWarning();
+    void showForceVectorWarning();
 };
 
 #endif // QGSLAYOUTDESIGNERDIALOG_H

src/app/layout/qgslayoutpropertieswidget.cpp

@@ -59,6 +59,7 @@ QgsLayoutPropertiesWidget::QgsLayoutPropertiesWidget( QWidget *parent, QgsLayout
   connect( mGenerateWorldFileCheckBox, &QCheckBox::toggled, this, &QgsLayoutPropertiesWidget::worldFileToggled );
 
   connect( mRasterizeCheckBox, &QCheckBox::toggled, this, &QgsLayoutPropertiesWidget::rasteriseToggled );
+  connect( mForceVectorCheckBox, &QCheckBox::toggled, this, &QgsLayoutPropertiesWidget::forceVectorToggled );
 
   mTopMarginSpinBox->setValue( topMargin );
   mMarginUnitsComboBox->linkToWidget( mTopMarginSpinBox );
@@ -93,6 +94,19 @@ void QgsLayoutPropertiesWidget::updateGui()
 
   bool rasterise = mLayout->customProperty( QStringLiteral( "rasterise" ), false ).toBool();
   whileBlocking( mRasterizeCheckBox )->setChecked( rasterise );
+
+  bool forceVectors = mLayout->customProperty( QStringLiteral( "forceVector" ), false ).toBool();
+  whileBlocking( mForceVectorCheckBox )->setChecked( forceVectors );
+
+  if ( rasterise )
+  {
+    mForceVectorCheckBox->setChecked( false );
+    mForceVectorCheckBox->setEnabled( false );
+  }
+  else
+  {
+    mForceVectorCheckBox->setEnabled( true );
+  }
 }
 
 void QgsLayoutPropertiesWidget::updateSnappingElements()
@@ -197,6 +211,21 @@ void QgsLayoutPropertiesWidget::worldFileToggled()
 void QgsLayoutPropertiesWidget::rasteriseToggled()
 {
   mLayout->setCustomProperty( QStringLiteral( "rasterise" ), mRasterizeCheckBox->isChecked() );
+
+  if ( mRasterizeCheckBox->isChecked() )
+  {
+    mForceVectorCheckBox->setChecked( false );
+    mForceVectorCheckBox->setEnabled( false );
+  }
+  else
+  {
+    mForceVectorCheckBox->setEnabled( true );
+  }
+}
+
+void QgsLayoutPropertiesWidget::forceVectorToggled()
+{
+  mLayout->setCustomProperty( QStringLiteral( "forceVector" ), mForceVectorCheckBox->isChecked() );
 }
 
 void QgsLayoutPropertiesWidget::blockSignals( bool block )

src/app/layout/qgslayoutpropertieswidget.h

@@ -47,6 +47,7 @@ class QgsLayoutPropertiesWidget: public QgsPanelWidget, private Ui::QgsLayoutWid
     void dpiChanged( int value );
     void worldFileToggled();
     void rasteriseToggled();
+    void forceVectorToggled();
 
   private:
 

src/core/layout/qgslayoutcontext.h

@@ -45,6 +45,7 @@ class CORE_EXPORT QgsLayoutContext : public QObject
       FlagOutlineOnly = 1 << 2, //!< Render items as outlines only.
       FlagAntialiasing = 1 << 3, //!< Use antialiasing when drawing items.
       FlagUseAdvancedEffects = 1 << 4, //!< Enable advanced effects such as blend modes.
+      FlagForceVectorOutput = 1 << 5, //!< Force output in vector format where possible, even if items require rasterization to keep their correct appearance.
     };
     Q_DECLARE_FLAGS( Flags, Flag )
 

src/core/layout/qgslayoutexporter.cpp

@@ -310,7 +310,9 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::exportToPdf( const QString &f
   // If we are not printing as raster, temporarily disable advanced effects
   // as QPrinter does not support composition modes and can result
   // in items missing from the output
-  mLayout->context().setFlag( QgsLayoutContext::FlagUseAdvancedEffects, settings.rasteriseWholeImage );
+  mLayout->context().setFlag( QgsLayoutContext::FlagUseAdvancedEffects, !settings.forceVectorOutput );
+
+  mLayout->context().setFlag( QgsLayoutContext::FlagForceVectorOutput, settings.forceVectorOutput );
 
   QPrinter printer;
   preparePrintAsPdf( printer, filePath );
@@ -322,7 +324,7 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::exportToPdf( const QString &f
     return PrintError;
   }
 
-  ExportResult result = printPrivate( printer, p, false, settings.dpi, settings.rasteriseWholeImage );
+  ExportResult result = printPrivate( printer, p, false, settings.dpi, settings.rasterizeWholeImage );
   p.end();
 
 #if 0//TODO

src/core/layout/qgslayoutexporter.h

@@ -216,9 +216,22 @@ class CORE_EXPORT QgsLayoutExporter
       //! Resolution to export layout at. If dpi <= 0 the default layout dpi will be used.
       double dpi = -1;
 
-      //! Set to true to force whole layout to be rasterized while exporting
+      /**
+       * Set to true to force whole layout to be rasterized while exporting.
+       *
+       * This option is mutually exclusive with forceVectorOutput.
+       */
       bool rasterizeWholeImage = false;
 
+      /**
+       * Set to true to force vector object exports, even when the resultant appearance will differ
+       * from the layout. If false, some items may be rasterized in order to maintain their
+       * correct appearance in the output.
+       *
+       * This option is mutually exclusive with rasterizeWholeImage.
+       */
+      bool forceVectorOutput = false;
+
       /**
        * Layout context flags, which control how the export will be created.
        */

src/core/layout/qgslayoutitem.cpp

@@ -242,18 +242,32 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
     return;
   }
 
-  double destinationDpi = itemStyle->matrix.m11() * 25.4;
+  bool previewRender = !mLayout || mLayout->context().isPreviewRender();
+  double destinationDpi = previewRender ? itemStyle->matrix.m11() * 25.4 : mLayout->context().dpi();
   bool useImageCache = false;
+  bool forceRasterOutput = containsAdvancedEffects() && ( !mLayout || !( mLayout->context().flags() & QgsLayoutContext::FlagForceVectorOutput ) );
 
-  if ( useImageCache )
+  if ( useImageCache || forceRasterOutput )
   {
-    double widthInPixels = boundingRect().width() * itemStyle->matrix.m11();
-    double heightInPixels = boundingRect().height() * itemStyle->matrix.m11();
+    double widthInPixels = 0;
+    double heightInPixels = 0;
+
+    if ( previewRender )
+    {
+      widthInPixels = boundingRect().width() * itemStyle->matrix.m11();
+      heightInPixels = boundingRect().height() * itemStyle->matrix.m11();
+    }
+    else
+    {
+      double layoutUnitsToPixels = mLayout ? mLayout->convertFromLayoutUnits( 1, QgsUnitTypes::LayoutPixels ).length() : destinationDpi / 25.4;
+      widthInPixels = boundingRect().width() * layoutUnitsToPixels;
+      heightInPixels = boundingRect().height() * layoutUnitsToPixels;
+    }
 
     // limit size of image for better performance
-    double scale = 1.0;
-    if ( widthInPixels > CACHE_SIZE_LIMIT || heightInPixels > CACHE_SIZE_LIMIT )
+    if ( previewRender && ( widthInPixels > CACHE_SIZE_LIMIT || heightInPixels > CACHE_SIZE_LIMIT ) )
     {
+      double scale = 1.0;
       if ( widthInPixels > heightInPixels )
       {
         scale = widthInPixels / CACHE_SIZE_LIMIT;
@@ -269,7 +283,7 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
       destinationDpi = destinationDpi / scale;
     }
 
-    if ( !mItemCachedImage.isNull() && qgsDoubleNear( mItemCacheDpi, destinationDpi ) )
+    if ( previewRender && !mItemCachedImage.isNull() && qgsDoubleNear( mItemCacheDpi, destinationDpi ) )
     {
       // can reuse last cached image
       QgsRenderContext context = QgsLayoutUtils::createRenderContextForMap( nullptr, painter, destinationDpi );
@@ -284,13 +298,11 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
     }
     else
     {
-      mItemCacheDpi = destinationDpi;
-
-      mItemCachedImage = QImage( widthInPixels, heightInPixels, QImage::Format_ARGB32 );
-      mItemCachedImage.fill( Qt::transparent );
-      mItemCachedImage.setDotsPerMeterX( 1000 * destinationDpi * 25.4 );
-      mItemCachedImage.setDotsPerMeterY( 1000 * destinationDpi * 25.4 );
-      QPainter p( &mItemCachedImage );
+      QImage image = QImage( widthInPixels, heightInPixels, QImage::Format_ARGB32 );
+      image.fill( Qt::transparent );
+      image.setDotsPerMeterX( 1000 * destinationDpi * 25.4 );
+      image.setDotsPerMeterY( 1000 * destinationDpi * 25.4 );
+      QPainter p( &image );
 
       preparePainter( &p );
       QgsRenderContext context = QgsLayoutUtils::createRenderContextForLayout( nullptr, &p, destinationDpi );
@@ -306,8 +318,14 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
       // scale painter from mm to dots
       painter->scale( 1.0 / context.scaleFactor(), 1.0 / context.scaleFactor() );
       painter->drawImage( boundingRect().x() * context.scaleFactor(),
-                          boundingRect().y() * context.scaleFactor(), mItemCachedImage );
+                          boundingRect().y() * context.scaleFactor(), image );
       painter->restore();
+
+      if ( previewRender )
+      {
+        mItemCacheDpi = destinationDpi;
+        mItemCachedImage = image;
+      }
     }
   }
   else
@@ -842,7 +860,12 @@ void QgsLayoutItem::setExcludeFromExports( bool exclude )
 
 bool QgsLayoutItem::containsAdvancedEffects() const
 {
-  return blendMode() != QPainter::CompositionMode_SourceOver;
+  return false;
+}
+
+bool QgsLayoutItem::requiresRasterization() const
+{
+  return itemOpacity() < 1.0 || blendMode() != QPainter::CompositionMode_SourceOver;
 }
 
 double QgsLayoutItem::estimatedFrameBleed() const

src/core/layout/qgslayoutitem.h

@@ -748,9 +748,18 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
      *
      * Subclasses should ensure that implemented overrides of this method
      * also check the base class result.
+     *
+     * \see requiresRasterization()
      */
     virtual bool containsAdvancedEffects() const;
 
+    /**
+     * Returns true if the item is drawn in such a way that forces the whole layout
+     * to be rasterised when exporting to vector formats.
+     * \see containsAdvancedEffects()
+     */
+    virtual bool requiresRasterization() const;
+
     /**
      * Returns the estimated amount the item's frame bleeds outside the item's
      * actual rectangle. For instance, if the item has a 2mm frame stroke, then

src/core/layout/qgslayoutitemmap.cpp

@@ -798,19 +798,46 @@ void QgsLayoutItemMap::paint( QPainter *painter, const QStyleOptionGraphicsItem
     }
 
     QgsRectangle cExtent = extent();
-
     QSizeF size( cExtent.width() * mapUnitsToLayoutUnits(), cExtent.height() * mapUnitsToLayoutUnits() );
 
-    painter->save();
-    painter->translate( mXOffset, mYOffset );
+    if ( containsAdvancedEffects() && ( !mLayout || !( mLayout->context().flags() & QgsLayoutContext::FlagForceVectorOutput ) ) )
+    {
+      // rasterise
+      double destinationDpi = mLayout ? mLayout->context().dpi() : style->matrix.m11() * 25.4;
 
-    double dotsPerMM = paintDevice->logicalDpiX() / 25.4;
-    size *= dotsPerMM; // output size will be in dots (pixels)
-    painter->scale( 1 / dotsPerMM, 1 / dotsPerMM ); // scale painter from mm to dots
-    drawMap( painter, cExtent, size, paintDevice->logicalDpiX() );
+      double layoutUnitsToPixels = mLayout ? mLayout->convertFromLayoutUnits( 1, QgsUnitTypes::LayoutPixels ).length() : destinationDpi / 25.4;
+      double widthInPixels = boundingRect().width() * layoutUnitsToPixels;
+      double heightInPixels = boundingRect().height() * layoutUnitsToPixels;
+      QImage image = QImage( widthInPixels, heightInPixels, QImage::Format_ARGB32 );
+
+      image.fill( Qt::transparent );
+      image.setDotsPerMeterX( 1000 * destinationDpi / 25.4 );
+      image.setDotsPerMeterY( 1000 * destinationDpi / 25.4 );
+      QPainter p( &image );
+      double dotsPerMM = image.logicalDpiX() / 25.4;
+      drawMap( &p, cExtent, image.size(), destinationDpi );
+      p.end();
+
+      dotsPerMM = paintDevice->logicalDpiX() / 25.4;
+      painter->save();
+      painter->scale( 1 / dotsPerMM, 1 / dotsPerMM ); // scale painter from mm to dots
+      painter->drawImage( 0, 0, image );
+      painter->restore();
+
+    }
+    else
+    {
+      painter->save();
+      painter->translate( mXOffset, mYOffset );
+
+      double dotsPerMM = paintDevice->logicalDpiX() / 25.4;
+      size *= dotsPerMM; // output size will be in dots (pixels)
+      painter->scale( 1 / dotsPerMM, 1 / dotsPerMM ); // scale painter from mm to dots
+      drawMap( painter, cExtent, size, paintDevice->logicalDpiX() );
+
+      painter->restore();
+    }
 
-    //restore rotation
-    painter->restore();
     mDrawing = false;
   }
 

src/core/layout/qgslayoutitempicture.cpp

@@ -666,6 +666,14 @@ void QgsLayoutItemPicture::refreshDataDefinedProperty( const QgsLayoutObject::Da
   QgsLayoutItem::refreshDataDefinedProperty( property );
 }
 
+bool QgsLayoutItemPicture::containsAdvancedEffects() const
+{
+  if ( QgsLayoutItem::containsAdvancedEffects() )
+    return true;
+
+  return mMode == FormatSVG && itemOpacity() < 1.0;
+}
+
 void QgsLayoutItemPicture::setPicturePath( const QString &path )
 {
   mSourcePath = path;

src/core/layout/qgslayoutitempicture.h

@@ -265,6 +265,7 @@ class CORE_EXPORT QgsLayoutItemPicture: public QgsLayoutItem
     void recalculateSize();
 
     void refreshDataDefinedProperty( const QgsLayoutObject::DataDefinedProperty property = QgsLayoutObject::AllProperties ) override;
+    bool containsAdvancedEffects() const override;
 
   signals:
     //! Is emitted on picture rotation change

src/ui/layout/qgslayoutwidgetbase.ui

@@ -53,9 +53,9 @@
       <property name="geometry">
        <rect>
         <x>0</x>
-        <y>0</y>
+        <y>-316</y>
         <width>297</width>
-        <height>778</height>
+        <height>810</height>
        </rect>
       </property>
       <layout class="QVBoxLayout" name="verticalLayout_2">
@@ -210,7 +210,7 @@
           <string>Export settings</string>
          </property>
          <layout class="QGridLayout" name="gridLayout_3">
-          <item row="3" column="0" colspan="2">
+          <item row="4" column="0" colspan="2">
            <widget class="QCheckBox" name="mGenerateWorldFileCheckBox">
             <property name="sizePolicy">
              <sizepolicy hsizetype="Minimum" vsizetype="Preferred">
@@ -251,8 +251,21 @@
           </item>
           <item row="2" column="0" colspan="2">
            <widget class="QCheckBox" name="mRasterizeCheckBox">
+            <property name="toolTip">
+             <string>If checked, exports from this layout will be rasterized.</string>
+            </property>
             <property name="text">
-             <string>Export as raster</string>
+             <string>Print as raster</string>
+            </property>
+           </widget>
+          </item>
+          <item row="3" column="0" colspan="2">
+           <widget class="QCheckBox" name="mForceVectorCheckBox">
+            <property name="toolTip">
+             <string>If checked, the layout will always be kept as vector objects when exported to a compatible format, even if the appearance of the resultant file does not match the layouts settings. If unchecked, some elements in the layout may be rasterised in order to keep their appearance intact.</string>
+            </property>
+            <property name="text">
+             <string>Always export as vectors</string>
             </property>
            </widget>
           </item>
@@ -445,6 +458,7 @@
   <tabstop>mSnapToleranceSpinBox</tabstop>
   <tabstop>mResolutionSpinBox</tabstop>
   <tabstop>mRasterizeCheckBox</tabstop>
+  <tabstop>mForceVectorCheckBox</tabstop>
   <tabstop>mGenerateWorldFileCheckBox</tabstop>
   <tabstop>mMarginUnitsComboBox</tabstop>
   <tabstop>mTopMarginSpinBox</tabstop>