Ensure that item painter is correctly scaled so that painter units are pixels

Author: nyalldawson

python/core/layout/qgslayoutitem.sip

@@ -173,6 +173,8 @@ class QgsLayoutItem : QgsLayoutObject, QGraphicsRectItem
     virtual void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle = 0 ) = 0;
 %Docstring
  Draws the item's contents using the specified render ``context``.
+ Note that the context's painter has been scaled so that painter units are pixels.
+ Use the QgsRenderContext methods to convert from millimeters or other units to the painter's units.
 %End
 
     virtual void setFixedSize( const QgsLayoutSize &size );

src/core/layout/qgslayoutitem.cpp

@@ -18,11 +18,14 @@
 #include "qgslayout.h"
 #include "qgslayoututils.h"
 #include <QPainter>
+#include <QStyleOptionGraphicsItem>
 
 QgsLayoutItem::QgsLayoutItem( QgsLayout *layout )
   : QgsLayoutObject( layout )
   , QGraphicsRectItem( 0 )
 {
+  // needed to access current view transform during paint operations
+  setFlags( flags() | QGraphicsItem::ItemUsesExtendedStyleOption );
   setCacheMode( QGraphicsItem::DeviceCoordinateCache );
 
   //record initial position
@@ -50,7 +53,10 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
   }
   else
   {
-    QgsRenderContext context = QgsLayoutUtils::createRenderContextForLayout( mLayout, painter );
+    double destinationDpi = itemStyle->matrix.m11() * 25.4;
+    QgsRenderContext context = QgsLayoutUtils::createRenderContextForMap( nullptr, painter, destinationDpi );
+    // scale painter from mm to dots
+    painter->scale( 1.0 / context.scaleFactor(), 1.0 / context.scaleFactor() );
     draw( context, itemStyle );
   }
 

src/core/layout/qgslayoutitem.h

@@ -186,6 +186,8 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
 
     /**
      * Draws the item's contents using the specified render \a context.
+     * Note that the context's painter has been scaled so that painter units are pixels.
+     * Use the QgsRenderContext methods to convert from millimeters or other units to the painter's units.
      */
     virtual void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle = nullptr ) = 0;
 

src/core/layout/qgslayoutitemregistry.cpp

@@ -15,6 +15,8 @@
  ***************************************************************************/
 
 #include "qgslayoutitemregistry.h"
+#include "qgsgloweffect.h"
+#include "qgseffectstack.h"
 #include <QPainter>
 
 QgsLayoutItemRegistry::QgsLayoutItemRegistry( QObject *parent )
@@ -98,13 +100,24 @@ TestLayoutItem::TestLayoutItem( QgsLayout *layout )
 void TestLayoutItem::draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle )
 {
   Q_UNUSED( itemStyle );
+
+  QgsEffectStack stack;
+  stack.appendEffect( new QgsDrawSourceEffect() );
+  stack.appendEffect( new QgsInnerGlowEffect() );
+  stack.begin( context );
+
   QPainter *painter = context.painter();
 
   painter->save();
   painter->setRenderHint( QPainter::Antialiasing, false );
   painter->setPen( Qt::NoPen );
   painter->setBrush( mColor );
-  painter->drawRect( rect() );
+
+  double scale = context.convertToPainterUnits( 1, QgsUnitTypes::RenderMillimeters );
+  QRectF r = QRectF( rect().left() * scale, rect().top() * scale,
+                     rect().width() * scale, rect().height() * scale );
+  painter->drawRect( r );
   painter->restore();
+  stack.end( context );
 }
 ///@endcond