[composer] Use reference map when creating render context for

draw shape/arrow/nodes/paper symbols

This commit removes some more instances where changes in the
canvas affect compositions. Previously the symbols drawn
in shape/arrow/etc items were using the scale from the canvas.
This meant that the appearance of these items in composer
would change depending on canvas zoom if they used symbols
with map unit sizes.

Now they take their map scale from the composition's reference
map. While this has the nice side effect that now map units
can be used in the appearance of these items and they're
guaranteed to match up with the reference map item, the main
intention here is to remove more of the forced links between
compositions (core) and the main canvas (app).

python/core/composer/qgscomposerutils.sip

@@ -243,4 +243,11 @@ class QgsComposerUtils
      */
     static void drawText( QPainter* painter, const QRectF& rect, const QString& text, const QFont& font, const QColor& color = QColor(), const Qt::AlignmentFlag halignment = Qt::AlignLeft, const Qt::AlignmentFlag valignment = Qt::AlignTop, const int flags = Qt::TextWordWrap );
 
+    /**
+     * Creates a render context suitable for the specified composition and QPainter destination.
+     * This method returns a new QgsRenderContext which matches the scale and settings from the composition's
+     * QgsComposition::referenceMap().
+     * @note added in QGIS 3.0
+     */
+    static QgsRenderContext createRenderContext( QgsComposition* composition, QPainter& painter );
 };

src/core/composer/qgscomposerarrow.cpp

@@ -182,12 +182,9 @@ void QgsComposerArrow::drawLine( QPainter *painter )
   painter->scale( 1 / dotsPerMM, 1 / dotsPerMM ); //scale painter from mm to dots
 
   //setup render context
-  QgsMapSettings ms = mComposition->mapSettings();
-  //context units should be in dots
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
-  context.setPainter( painter );
+
   QgsExpressionContext expressionContext = createExpressionContext();
   context.setExpressionContext( expressionContext );
 

src/core/composer/qgscomposernodesitem.cpp

@@ -137,11 +137,7 @@ void QgsComposerNodesItem::drawNodes( QPainter *painter ) const
   symbol.data()->setSize( rectSize );
   symbol.data()->setAngle( 45 );
 
-  QgsMapSettings ms = mComposition->mapSettings();
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( painter );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
 
   QgsExpressionContext expressionContext = createExpressionContext();
@@ -172,11 +168,7 @@ void QgsComposerNodesItem::drawSelectedNode( QPainter *painter ) const
   symbol.reset( QgsMarkerSymbol::createSimple( properties ) );
   symbol.data()->setSize( rectSize );
 
-  QgsMapSettings ms = mComposition->mapSettings();
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( painter );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
 
   QgsExpressionContext expressionContext = createExpressionContext();

src/core/composer/qgscomposerpolygon.cpp

@@ -73,13 +73,8 @@ void QgsComposerPolygon::_draw( QPainter *painter )
   //setup painter scaling to dots so that raster symbology is drawn to scale
   const double dotsPerMM = painter->device()->logicalDpiX() / 25.4;
 
-  QgsMapSettings ms = mComposition->mapSettings();
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( painter );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
-
   context.setExpressionContext( createExpressionContext() );
 
   painter->scale( 1 / dotsPerMM, 1 / dotsPerMM ); // scale painter from mm to dots

src/core/composer/qgscomposerpolyline.cpp

@@ -100,11 +100,7 @@ void QgsComposerPolyline::_draw( QPainter *painter )
 {
   double dotsPerMM = painter->device()->logicalDpiX() / 25.4;
 
-  QgsMapSettings ms = mComposition->mapSettings();
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( painter );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
 
   QgsExpressionContext expressionContext = createExpressionContext();

src/core/composer/qgscomposershape.cpp

@@ -21,6 +21,7 @@
 #include "qgssymbollayerutils.h"
 #include "qgscomposermodel.h"
 #include "qgsmapsettings.h"
+#include "qgscomposerutils.h"
 #include <QPainter>
 
 QgsComposerShape::QgsComposerShape( QgsComposition* composition )
@@ -178,11 +179,7 @@ void QgsComposerShape::drawShapeUsingSymbol( QPainter* p )
   double dotsPerMM = p->device()->logicalDpiX() / 25.4;
 
   //setup render context
-  QgsMapSettings ms = mComposition->mapSettings();
-  //context units should be in dots
-  ms.setOutputDpi( p->device()->logicalDpiX() );
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( p );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *p );
   context.setForceVectorOutput( true );
   QgsExpressionContext expressionContext = createExpressionContext();
   context.setExpressionContext( expressionContext );

src/core/composer/qgscomposerutils.cpp

@@ -18,6 +18,8 @@
 #include "qgscomposerutils.h"
 #include "qgscomposition.h"
 #include "qgsdatadefined.h"
+#include "qgsmapsettings.h"
+#include "qgscomposermap.h"
 #include <QPainter>
 
 #define FONT_WORKAROUND_SCALE 10 //scale factor for upscaling fontsize and downscaling painter
@@ -545,3 +547,24 @@ void QgsComposerUtils::drawText( QPainter *painter, const QRectF &rect, const QS
   painter->drawText( scaledRect, halignment | valignment | flags, text );
   painter->restore();
 }
+
+QgsRenderContext QgsComposerUtils::createRenderContext( QgsComposition* composition, QPainter &painter )
+{
+  QgsComposerMap* referenceMap = composition ? composition->referenceMap() : nullptr;
+  if ( !referenceMap )
+  {
+    return QgsRenderContext::fromQPainter( &painter );
+  }
+
+  int dpi = painter.device()->logicalDpiX();
+  double dotsPerMM = dpi / 25.4;
+
+  // get map settings from reference map
+  QgsRectangle extent = *( referenceMap->currentMapExtent() );
+  QSizeF mapSizeMM = referenceMap->rect().size();
+  QgsMapSettings ms = referenceMap->mapSettings( extent, mapSizeMM * dotsPerMM, dpi );
+
+  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
+  context.setPainter( &painter );
+  return context;
+}

src/core/composer/qgscomposerutils.h

@@ -19,6 +19,7 @@
 
 #include "qgis_core.h"
 #include "qgscomposition.h" //for page size and orientation enums
+#include "qgsrendercontext.h"
 #include <QPointF>
 #include <QRectF>
 
@@ -265,6 +266,14 @@ class CORE_EXPORT QgsComposerUtils
      */
     static void drawText( QPainter* painter, const QRectF& rect, const QString& text, const QFont& font, const QColor& color = QColor(), const Qt::AlignmentFlag halignment = Qt::AlignLeft, const Qt::AlignmentFlag valignment = Qt::AlignTop, const int flags = Qt::TextWordWrap );
 
+    /**
+     * Creates a render context suitable for the specified composition and QPainter destination.
+     * This method returns a new QgsRenderContext which matches the scale and settings from the composition's
+     * QgsComposition::referenceMap().
+     * @note added in QGIS 3.0
+     */
+    static QgsRenderContext createRenderContext( QgsComposition* composition, QPainter& painter );
+
 };
 
 #endif

src/core/composer/qgspaperitem.cpp

@@ -20,6 +20,7 @@
 #include "qgsstyle.h"
 #include "qgslogger.h"
 #include "qgsmapsettings.h"
+#include "qgscomposerutils.h"
 #include <QGraphicsRectItem>
 #include <QGraphicsView>
 #include <QPainter>
@@ -155,12 +156,9 @@ void QgsPaperItem::paint( QPainter* painter, const QStyleOptionGraphicsItem* ite
   double dotsPerMM = painter->device()->logicalDpiX() / 25.4;
 
   //setup render context
-  QgsMapSettings ms = mComposition->mapSettings();
-  //context units should be in dots
-  ms.setOutputDpi( painter->device()->logicalDpiX() );
-  QgsRenderContext context = QgsRenderContext::fromMapSettings( ms );
-  context.setPainter( painter );
+  QgsRenderContext context = QgsComposerUtils::createRenderContext( mComposition, *painter );
   context.setForceVectorOutput( true );
+
   QgsExpressionContext expressionContext = createExpressionContext();
   context.setExpressionContext( expressionContext );
 

tests/src/core/testqgscomposerutils.cpp

@@ -18,10 +18,12 @@
 #include "qgsapplication.h" //for standard test font
 #include "qgscomposerutils.h"
 #include "qgscomposition.h"
+#include "qgscomposermap.h"
 #include "qgsmultirenderchecker.h"
 #include "qgsdatadefined.h"
 #include "qgsfontutils.h"
 #include "qgsproject.h"
+#include "qgstestutils.h"
 #include <QObject>
 #include "qgstest.h"
 #include <QMap>
@@ -61,6 +63,7 @@ class TestQgsComposerUtils : public QObject
     void textHeightMM(); //test calculating text height in mm
     void drawTextPos(); //test drawing text at a pos
     void drawTextRect(); //test drawing text in a rect
+    void createRenderContext();
 
   private:
     bool renderCheck( const QString& testName, QImage &image, int mismatchCount = 0 );
@@ -701,6 +704,42 @@ void TestQgsComposerUtils::drawTextRect()
   QVERIFY( renderCheck( "composerutils_drawtext_rectflag", testImage, 100 ) );
 }
 
+void TestQgsComposerUtils::createRenderContext()
+{
+  QImage testImage = QImage( 250, 250, QImage::Format_RGB32 );
+  testImage.setDotsPerMeterX( 150 / 25.4 * 1000 );
+  testImage.setDotsPerMeterY( 150 / 25.4 * 1000 );
+  QPainter p( &testImage );
+
+  // no composition
+  QgsRenderContext rc = QgsComposerUtils::createRenderContext( nullptr, p );
+  QGSCOMPARENEAR( rc.scaleFactor(), 150 / 25.4, 0.001 );
+  QCOMPARE( rc.painter(), &p );
+
+  //create composition with no reference map
+  QgsRectangle extent( 2000, 2800, 2500, 2900 );
+  QgsMapSettings ms;
+  ms.setExtent( extent );
+  QgsComposition* composition = new QgsComposition( ms, QgsProject::instance() );
+  rc = QgsComposerUtils::createRenderContext( composition, p );
+  QGSCOMPARENEAR( rc.scaleFactor(), 150 / 25.4, 0.001 );
+  QCOMPARE( rc.painter(), &p );
+
+  // add a reference map
+  QgsComposerMap* map = new QgsComposerMap( composition );
+  map->setNewExtent( extent );
+  map->setSceneRect( QRectF( 30, 60, 200, 100 ) );
+  composition->addComposerMap( map );
+  composition->setReferenceMap( map );
+
+  rc = QgsComposerUtils::createRenderContext( composition, p );
+  QGSCOMPARENEAR( rc.scaleFactor(), 150 / 25.4, 0.001 );
+  QGSCOMPARENEAR( rc.rendererScale(), map->scale(), 100000 );
+  QCOMPARE( rc.painter(), &p );
+
+  p.end();
+}
+
 bool TestQgsComposerUtils::renderCheck( const QString& testName, QImage &image, int mismatchCount )
 {
   mReport += "<h2>" + testName + "</h2>\n";