Fix html labels rendering before they are fully loaded. Prevents missing images in html labels when composer layout is output for the first time.

nyalldawson · nyalldawson · commit f7732d3a2724 · 2013-04-09T13:31:47.000+10:00
diff --git a/src/core/composer/qgscomposerlabel.cpp b/src/core/composer/qgscomposerlabel.cpp
@@ -24,10 +24,11 @@
 #include <QPainter>
 #include <QWebFrame>
 #include <QWebPage>
+#include <QEventLoop>
 
 QgsComposerLabel::QgsComposerLabel( QgsComposition *composition ):
     QgsComposerItem( composition ), mHtmlState( 0 ), mHtmlUnitsToMM( 1.0 ),
-    mMargin( 1.0 ), mFontColor( QColor( 0, 0, 0 ) ),
+    mHtmlLoaded( false ), mMargin( 1.0 ), mFontColor( QColor( 0, 0, 0 ) ),
     mHAlignment( Qt::AlignLeft ), mVAlignment( Qt::AlignTop ),
     mExpressionFeature( 0 ), mExpressionLayer( 0 )
 {
@@ -64,6 +65,11 @@ void QgsComposerLabel::paint( QPainter* painter, const QStyleOptionGraphicsItem*
 
     QWebPage* webPage = new QWebPage();
 
+    //Setup event loop and timeout for rendering html
+    QEventLoop loop;
+    QTimer timeoutTimer;
+    timeoutTimer.setSingleShot( true );
+
     //This makes the background transparent. Found on http://blog.qt.digia.com/blog/2009/06/30/transparent-qwebview-or-qwebpage/
     QPalette palette = webPage->palette();
     palette.setBrush( QPalette::Base, Qt::transparent );
@@ -74,7 +80,30 @@ void QgsComposerLabel::paint( QPainter* painter, const QStyleOptionGraphicsItem*
     webPage->mainFrame()->setZoomFactor( 10.0 );
     webPage->mainFrame()->setScrollBarPolicy( Qt::Horizontal, Qt::ScrollBarAlwaysOff );
     webPage->mainFrame()->setScrollBarPolicy( Qt::Vertical, Qt::ScrollBarAlwaysOff );
+
+    //Connect timeout and webpage loadFinished signals to loop
+    connect( &timeoutTimer, SIGNAL( timeout() ), &loop, SLOT( quit() ) );
+    connect( webPage, SIGNAL( loadFinished( bool ) ), &loop, SLOT( quit() ) );
+
+    //mHtmlLoaded tracks whether the QWebPage has completed loading
+    //its html contents, set it initially to false. The loadingHtmlFinished slot will
+    //set this to true after html is loaded.
+    mHtmlLoaded = false;
+    connect( webPage, SIGNAL( loadFinished( bool ) ), SLOT( loadingHtmlFinished( bool ) ) );
+
     webPage->mainFrame()->setHtml( displayText() );
+
+    //For very basic html labels with no external assets, the html load will already be
+    //complete before we even get a chance to start the QEventLoop. Make sure we check
+    //this before starting the loop
+    if ( !mHtmlLoaded )
+    {
+      // Start a 20 second timeout in case html loading will never complete
+      timeoutTimer.start( 20000 );
+      // Pause until html is loaded
+      loop.exec();
+    }
+
     webPage->mainFrame()->render( painter );//DELETE WEBPAGE ?
   }
   else
@@ -90,9 +119,6 @@ void QgsComposerLabel::paint( QPainter* painter, const QStyleOptionGraphicsItem*
     drawText( painter, painterRect, displayText(), mFont, mHAlignment, mVAlignment );
   }
 
-
-
-
   painter->restore();
 
   drawFrame( painter );
@@ -102,6 +128,13 @@ void QgsComposerLabel::paint( QPainter* painter, const QStyleOptionGraphicsItem*
   }
 }
 
+/*Track when QWebPage has finished loading its html contents*/
+void QgsComposerLabel::loadingHtmlFinished( bool result )
+{
+  Q_UNUSED (result);
+  mHtmlLoaded = true;
+}
+
 double QgsComposerLabel::htmlUnitsToMM()
 {
   if ( !mComposition )
diff --git a/src/core/composer/qgscomposerlabel.h b/src/core/composer/qgscomposerlabel.h
@@ -104,6 +104,9 @@ class CORE_EXPORT QgsComposerLabel: public QgsComposerItem
   public slots:
     virtual void setRotation( double r );
 
+  private slots:
+    void loadingHtmlFinished( bool );
+
   private:
     // Text
     QString mText;
@@ -112,6 +115,7 @@ class CORE_EXPORT QgsComposerLabel: public QgsComposerItem
     int mHtmlState;
     double mHtmlUnitsToMM;
     double htmlUnitsToMM(); //calculate scale factor
+    bool mHtmlLoaded;
 
     /**Helper function to calculate x/y shift for adjustSizeToText() depending on rotation, current size and alignment*/
     void itemShiftAdjustSize( double newWidth, double newHeight, double& xShift, double& yShift ) const;
@@ -142,6 +146,8 @@ class CORE_EXPORT QgsComposerLabel: public QgsComposerItem
     QgsFeature* mExpressionFeature;
     QgsVectorLayer* mExpressionLayer;
     QMap<QString, QVariant> mSubstitutions;
+
+
 };
 
 #endif
