Change QgsLayoutItem::draw to use a renderContext instead of

direct QPainter argument

This will make use of other rendering code within layout items
much easier - since symbology/text renderer/diagrams/etc all
require QgsRenderContexts for use, it makes sense for
layout item rendering to also use this approach.

This also avoids lots of duplicate code which was scattered
throughout different composer item types to manually handle
creation of QgsRenderContexts when required.

python/core/layout/qgslayoutitem.sip

@@ -170,9 +170,9 @@ class QgsLayoutItem : QgsLayoutObject, QGraphicsRectItem
  @param painter destination QPainter
 %End
 
-    virtual void draw( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget ) = 0;
+    virtual void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle = 0 ) = 0;
 %Docstring
- Draws the item's contents on a specified ``painter``.
+ Draws the item's contents using the specified render ``context``.
 %End
 
     virtual void setFixedSize( const QgsLayoutSize &size );

src/core/layout/qgslayoutitem.cpp

@@ -33,7 +33,7 @@ QgsLayoutItem::QgsLayoutItem( QgsLayout *layout )
   initConnectionsToLayout();
 }
 
-void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget )
+void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget * )
 {
   if ( !painter || !painter->device() )
   {
@@ -50,7 +50,8 @@ void QgsLayoutItem::paint( QPainter *painter, const QStyleOptionGraphicsItem *it
   }
   else
   {
-    draw( painter, itemStyle, pWidget );
+    QgsRenderContext context = QgsLayoutUtils::createRenderContextForLayout( mLayout, painter );
+    draw( context, itemStyle );
   }
 
   painter->restore();

src/core/layout/qgslayoutitem.h

@@ -21,6 +21,7 @@
 #include "qgslayoutobject.h"
 #include "qgslayoutsize.h"
 #include "qgslayoutpoint.h"
+#include "qgsrendercontext.h"
 #include <QGraphicsRectItem>
 
 class QgsLayout;
@@ -184,9 +185,9 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     virtual void drawDebugRect( QPainter *painter );
 
     /**
-     * Draws the item's contents on a specified \a painter.
+     * Draws the item's contents using the specified render \a context.
      */
-    virtual void draw( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget ) = 0;
+    virtual void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle = nullptr ) = 0;
 
     /**
      * Sets a fixed \a size for the layout item, which prevents it from being freely

src/core/layout/qgslayoutitemregistry.cpp

@@ -95,10 +95,11 @@ TestLayoutItem::TestLayoutItem( QgsLayout *layout )
   mColor = QColor::fromHsv( h, s, v );
 }
 
-void TestLayoutItem::draw( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget )
+void TestLayoutItem::draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle )
 {
   Q_UNUSED( itemStyle );
-  Q_UNUSED( pWidget );
+  QPainter *painter = context.painter();
+
   painter->save();
   painter->setRenderHint( QPainter::Antialiasing, false );
   painter->setPen( Qt::NoPen );

src/core/layout/qgslayoutitemregistry.h

@@ -267,7 +267,7 @@ class TestLayoutItem : public QgsLayoutItem
 
     //implement pure virtual methods
     int type() const { return QgsLayoutItemRegistry::LayoutItem + 102; }
-    void draw( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget );
+    void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem *itemStyle = nullptr );
 
   private:
     QColor mColor;

tests/src/core/testqgslayoutitem.cpp

@@ -69,10 +69,11 @@ class TestQgsLayoutItem: public QObject
 
         //implement pure virtual methods
         int type() const { return QgsLayoutItemRegistry::LayoutItem + 101; }
-        void draw( QPainter *painter, const QStyleOptionGraphicsItem *itemStyle, QWidget *pWidget )
+
+      protected:
+        void draw( QgsRenderContext &context, const QStyleOptionGraphicsItem * = nullptr ) override
         {
-          Q_UNUSED( itemStyle );
-          Q_UNUSED( pWidget );
+          QPainter *painter = context.painter();
           painter->save();
           painter->setRenderHint( QPainter::Antialiasing, false );
           painter->setPen( Qt::NoPen );

tests/src/gui/testqgslayoutview.cpp

@@ -242,7 +242,7 @@ class TestItem : public QgsLayoutItem
 
     //implement pure virtual methods
     int type() const override { return QgsLayoutItemRegistry::LayoutItem + 101; }
-    void draw( QPainter *, const QStyleOptionGraphicsItem *, QWidget * ) override
+    void draw( QgsRenderContext &, const QStyleOptionGraphicsItem * = nullptr ) override
     {    }
 };