Asyncronously render composer map previews

(Forward port from Sourcepole fork)

Author: manisandro

src/core/composer/qgscomposermap.cpp

@@ -206,12 +206,20 @@ void QgsComposerMap::cache()
     return;
   }
 
-  if ( mDrawing )
+  if ( mPainterJob )
   {
-    return;
+    if ( mPainterCancelWait )
+    {
+      return; // Already waiting
+    }
+    QgsDebugMsg( "Aborting composer painter job" );
+    mPainterCancelWait = true;
+    mPainterJob->cancel();
+    mPainterCancelWait = false;
   }
 
-  mDrawing = true;
+  Q_ASSERT( !mPainterJob );
+  Q_ASSERT( !mPainter );
 
   double horizontalVScaleFactor = horizontalViewScaleFactor();
   if ( horizontalVScaleFactor < 0 )
@@ -260,13 +268,24 @@ void QgsComposerMap::cache()
     mCacheImage.fill( QColor( 255, 255, 255, 0 ).rgba() );
   }
 
-  QPainter p( &mCacheImage );
+  mPainter = new QPainter( &mCacheImage );
+  QgsMapSettings settings( mapSettings( ext, QSizeF( w, h ), mCacheImage.logicalDpiX() ) );
+  mPainterJob = new QgsMapRendererCustomPainterJob( settings, mPainter );
+  connect( mPainterJob, SIGNAL( finished() ), this, SLOT( painterJobFinished() ) );
+  QgsDebugMsg( "Starting new composer painter job" );
+  mPainterJob->start();
+}
 
-  draw( &p, ext, QSizeF( w, h ), mCacheImage.logicalDpiX() );
-  p.end();
+void QgsComposerMap::painterJobFinished()
+{
+  QgsDebugMsg( "Finished composer painter job" );
+  mPainter->end();
+  delete mPainterJob;
+  mPainterJob = nullptr;
+  delete mPainter;
+  mPainter = nullptr;
   mCacheUpdated = true;
-
-  mDrawing = false;
+  updateItem();
 }
 
 void QgsComposerMap::paint( QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *pWidget )
@@ -1031,8 +1050,10 @@ void QgsComposerMap::updateItem()
 
   if ( mPreviewMode != QgsComposerMap::Rectangle && !mCacheUpdated )
   {
+    QgsDebugMsg( "Requesting new cache image item" );
     cache();
   }
+  QgsDebugMsg( "Updating item" );
   QgsComposerItem::updateItem();
 }
 

src/core/composer/qgscomposermap.h

@@ -43,6 +43,7 @@ class QgsFillSymbol;
 class QgsLineSymbol;
 class QgsVectorLayer;
 class QgsAnnotation;
+class QgsMapRendererCustomPainterJob;
 
 /** \ingroup core
  *  \class QgsComposerMap
@@ -491,6 +492,8 @@ class CORE_EXPORT QgsComposerMap : public QgsComposerItem
   private slots:
     void layersAboutToBeRemoved( QList<QgsMapLayer *> layers );
 
+    void painterJobFinished();
+
   private:
 
     //! Unique identifier
@@ -587,6 +590,10 @@ class CORE_EXPORT QgsComposerMap : public QgsComposerItem
     //! Margin size for atlas driven extents (percentage of feature size) - when in auto scaling mode
     double mAtlasMargin = 0.10;
 
+    QPainter *mPainter = nullptr;
+    QgsMapRendererCustomPainterJob *mPainterJob = nullptr;
+    bool mPainterCancelWait = false;
+
     void init();
 
     //! Resets the item tooltip to reflect current map id