Fix SVG preview blocks QGIS (fix #14255)

Now SVG preview loading occurs in a background thread so that
dialogs can open instantly

Author: nyalldawson

src/core/qgsapplication.cpp

@@ -715,7 +715,7 @@ QStringList QgsApplication::svgPaths()
   }
 
   myPathList << ABISYM( mDefaultSvgPaths );
-  return myPathList;
+  return myPathList.toSet().toList();
 }
 
 /*!

src/gui/symbology-ng/qgssvgselectorwidget.cpp

@@ -32,29 +32,221 @@
 #include <QStyle>
 #include <QTime>
 
+// QgsSvgSelectorLoader
 
-//--- QgsSvgSelectorListModel
+///@cond PRIVATE
+QgsSvgSelectorLoader::QgsSvgSelectorLoader( QObject* parent )
+    : QThread( parent )
+    , mCancelled( false )
+    , mTimerThreshold( 0 )
+{
+}
+
+QgsSvgSelectorLoader::~QgsSvgSelectorLoader()
+{
+  stop();
+}
+
+void QgsSvgSelectorLoader::run()
+{
+  mCancelled = false;
+  mQueuedSvgs.clear();
+
+  // start with a small initial timeout (ms)
+  mTimerThreshold = 10;
+  mTimer.start();
+
+  loadPath( mPath );
+
+  if ( !mQueuedSvgs.isEmpty() )
+  {
+    // make sure we notify model of any remaining queued svgs (ie svgs added since last foundSvgs() signal was emitted)
+    emit foundSvgs( mQueuedSvgs );
+  }
+  mQueuedSvgs.clear();
+}
+
+void QgsSvgSelectorLoader::stop()
+{
+  mCancelled = true;
+  while ( isRunning() ) {}
+}
+
+void QgsSvgSelectorLoader::loadPath( const QString& path )
+{
+  if ( mCancelled )
+    return;
+
+  // QgsDebugMsg( QString( "loading path: %1" ).arg( path ) );
+
+  if ( path.isEmpty() )
+  {
+    QStringList svgPaths = QgsApplication::svgPaths();
+    Q_FOREACH ( const QString& svgPath, svgPaths )
+    {
+      if ( mCancelled )
+        return;
+
+      loadPath( svgPath );
+    }
+  }
+  else
+  {
+    loadImages( path );
+
+    QDir dir( path );
+    Q_FOREACH ( const QString& item, dir.entryList( QDir::Dirs | QDir::NoDotAndDotDot ) )
+    {
+      if ( mCancelled )
+        return;
+
+      QString newPath = dir.path() + '/' + item;
+      loadPath( newPath );
+      // QgsDebugMsg( QString( "added path: %1" ).arg( newPath ) );
+    }
+  }
+}
+
+void QgsSvgSelectorLoader::loadImages( const QString& path )
+{
+  QDir dir( path );
+  Q_FOREACH ( const QString& item, dir.entryList( QStringList( "*.svg" ), QDir::Files ) )
+  {
+    if ( mCancelled )
+      return;
+
+    // TODO test if it is correct SVG
+    QString svgPath = dir.path() + '/' + item;
+    // QgsDebugMsg( QString( "adding svg: %1" ).arg( svgPath ) );
+
+    // add it to the list of queued SVGs
+    mQueuedSvgs << svgPath;
+
+    // we need to avoid spamming the model with notifications about new svgs, so foundSvgs
+    // is only emitted for blocks of SVGs (otherwise the view goes all flickery)
+    if ( mTimer.elapsed() > mTimerThreshold )
+    {
+      emit foundSvgs( mQueuedSvgs );
+      mQueuedSvgs.clear();
+
+      // increase the timer threshold - this ensures that the first lots of svgs loaded are added
+      // to the view quickly, but as the list grows new svgs are added at a slower rate.
+      // ie, good for initial responsiveness but avoid being spammy as the list grows.
+      if ( mTimerThreshold < 1000 )
+        mTimerThreshold *= 2;
+      mTimer.restart();
+    }
+  }
+}
+
+
+//
+// QgsSvgGroupLoader
+//
+
+QgsSvgGroupLoader::QgsSvgGroupLoader( QObject* parent )
+    : QThread( parent )
+    , mCancelled( false )
+{
+
+}
+
+QgsSvgGroupLoader::~QgsSvgGroupLoader()
+{
+  stop();
+}
+
+void QgsSvgGroupLoader::run()
+{
+  mCancelled = false;
+
+  while ( !mCancelled && !mParentPaths.isEmpty() )
+  {
+    QString parentPath = mParentPaths.takeFirst();
+    loadGroup( parentPath );
+  }
+}
+
+void QgsSvgGroupLoader::stop()
+{
+  mCancelled = true;
+  while ( isRunning() ) {}
+}
+
+void QgsSvgGroupLoader::loadGroup( const QString& parentPath )
+{
+  QDir parentDir( parentPath );
+
+  Q_FOREACH ( const QString& item, parentDir.entryList( QDir::Dirs | QDir::NoDotAndDotDot ) )
+  {
+    if ( mCancelled )
+      return;
+
+    emit foundPath( parentPath, item );
+    mParentPaths.append( parentDir.path() + '/' + item );
+  }
+}
+
+///@endcond
+
+//,
+// QgsSvgSelectorListModel
+//
 
 QgsSvgSelectorListModel::QgsSvgSelectorListModel( QObject* parent )
     : QAbstractListModel( parent )
+    , mSvgLoader( new QgsSvgSelectorLoader( this ) )
 {
-  mSvgFiles = QgsSymbolLayerUtils::listSvgFiles();
+  mSvgLoader->setPath( QString() );
+  connect( mSvgLoader, SIGNAL( foundSvgs( QStringList ) ), this, SLOT( addSvgs( QStringList ) ) );
+  mSvgLoader->start();
 }
 
-// Constructor to create model for icons in a specific path
 QgsSvgSelectorListModel::QgsSvgSelectorListModel( QObject* parent, const QString& path )
     : QAbstractListModel( parent )
+    , mSvgLoader( new QgsSvgSelectorLoader( this ) )
 {
-  mSvgFiles = QgsSymbolLayerUtils::listSvgFilesAt( path );
+  mSvgLoader->setPath( path );
+  connect( mSvgLoader, SIGNAL( foundSvgs( QStringList ) ), this, SLOT( addSvgs( QStringList ) ) );
+  mSvgLoader->start();
 }
 
-int QgsSvgSelectorListModel::rowCount( const QModelIndex & parent ) const
+int QgsSvgSelectorListModel::rowCount( const QModelIndex& parent ) const
 {
   Q_UNUSED( parent );
   return mSvgFiles.count();
 }
 
-QVariant QgsSvgSelectorListModel::data( const QModelIndex & index, int role ) const
+QPixmap QgsSvgSelectorListModel::createPreview( const QString& entry ) const
+{
+  // render SVG file
+  QColor fill, outline;
+  double outlineWidth, fillOpacity, outlineOpacity;
+  bool fillParam, fillOpacityParam, outlineParam, outlineWidthParam, outlineOpacityParam;
+  bool hasDefaultFillColor = false, hasDefaultFillOpacity = false, hasDefaultOutlineColor = false,
+                             hasDefaultOutlineWidth = false, hasDefaultOutlineOpacity = false;
+  QgsSvgCache::instance()->containsParams( entry, fillParam, hasDefaultFillColor, fill,
+      fillOpacityParam, hasDefaultFillOpacity, fillOpacity,
+      outlineParam, hasDefaultOutlineColor, outline,
+      outlineWidthParam, hasDefaultOutlineWidth, outlineWidth,
+      outlineOpacityParam, hasDefaultOutlineOpacity, outlineOpacity );
+
+  //if defaults not set in symbol, use these values
+  if ( !hasDefaultFillColor )
+    fill = QColor( 200, 200, 200 );
+  fill.setAlphaF( hasDefaultFillOpacity ? fillOpacity : 1.0 );
+  if ( !hasDefaultOutlineColor )
+    outline = Qt::black;
+  outline.setAlphaF( hasDefaultOutlineOpacity ? outlineOpacity : 1.0 );
+  if ( !hasDefaultOutlineWidth )
+    outlineWidth = 0.2;
+
+  bool fitsInCache; // should always fit in cache at these sizes (i.e. under 559 px ^ 2, or half cache size)
+  const QImage& img = QgsSvgCache::instance()->svgAsImage( entry, 30.0, fill, outline, outlineWidth, 3.5 /*appr. 88 dpi*/, 1.0, fitsInCache );
+  return QPixmap::fromImage( img );
+}
+
+QVariant QgsSvgSelectorListModel::data( const QModelIndex& index, int role ) const
 {
   QString entry = mSvgFiles.at( index.row() );
 
@@ -63,31 +255,7 @@ QVariant QgsSvgSelectorListModel::data( const QModelIndex & index, int role ) co
     QPixmap pixmap;
     if ( !QPixmapCache::find( entry, pixmap ) )
     {
-      // render SVG file
-      QColor fill, outline;
-      double outlineWidth, fillOpacity, outlineOpacity;
-      bool fillParam, fillOpacityParam, outlineParam, outlineWidthParam, outlineOpacityParam;
-      bool hasDefaultFillColor = false, hasDefaultFillOpacity = false, hasDefaultOutlineColor = false,
-                                 hasDefaultOutlineWidth = false, hasDefaultOutlineOpacity = false;
-      QgsSvgCache::instance()->containsParams( entry, fillParam, hasDefaultFillColor, fill,
-          fillOpacityParam, hasDefaultFillOpacity, fillOpacity,
-          outlineParam, hasDefaultOutlineColor, outline,
-          outlineWidthParam, hasDefaultOutlineWidth, outlineWidth,
-          outlineOpacityParam, hasDefaultOutlineOpacity, outlineOpacity );
-
-      //if defaults not set in symbol, use these values
-      if ( !hasDefaultFillColor )
-        fill = QColor( 200, 200, 200 );
-      fill.setAlphaF( hasDefaultFillOpacity ? fillOpacity : 1.0 );
-      if ( !hasDefaultOutlineColor )
-        outline = Qt::black;
-      outline.setAlphaF( hasDefaultOutlineOpacity ? outlineOpacity : 1.0 );
-      if ( !hasDefaultOutlineWidth )
-        outlineWidth = 0.2;
-
-      bool fitsInCache; // should always fit in cache at these sizes (i.e. under 559 px ^ 2, or half cache size)
-      const QImage& img = QgsSvgCache::instance()->svgAsImage( entry, 30.0, fill, outline, outlineWidth, 3.5 /*appr. 88 dpi*/, 1.0, fitsInCache );
-      pixmap = QPixmap::fromImage( img );
+      pixmap = createPreview( entry );
       QPixmapCache::insert( entry, pixmap );
     }
 
@@ -101,18 +269,30 @@ QVariant QgsSvgSelectorListModel::data( const QModelIndex & index, int role ) co
   return QVariant();
 }
 
+void QgsSvgSelectorListModel::addSvgs( const QStringList& svgs )
+{
+  beginInsertRows( QModelIndex(), mSvgFiles.count(), mSvgFiles.count() + svgs.size() - 1 );
+  mSvgFiles.append( svgs );
+  endInsertRows();
+}
+
+
+
+
 
 //--- QgsSvgSelectorGroupsModel
 
 QgsSvgSelectorGroupsModel::QgsSvgSelectorGroupsModel( QObject* parent )
     : QStandardItemModel( parent )
+    , mLoader( new QgsSvgGroupLoader( this ) )
 {
   QStringList svgPaths = QgsApplication::svgPaths();
   QStandardItem *parentItem = invisibleRootItem();
+  QStringList parentPaths;
 
   for ( int i = 0; i < svgPaths.size(); i++ )
   {
-    QDir dir( svgPaths[i] );
+    QDir dir( svgPaths.at( i ) );
     QStandardItem *baseGroup;
 
     if ( dir.path().contains( QgsApplication::pkgDataPath() ) )
@@ -127,31 +307,41 @@ QgsSvgSelectorGroupsModel::QgsSvgSelectorGroupsModel( QObject* parent )
     {
       baseGroup = new QStandardItem( dir.dirName() );
     }
-    baseGroup->setData( QVariant( svgPaths[i] ) );
+    baseGroup->setData( QVariant( svgPaths.at( i ) ) );
     baseGroup->setEditable( false );
     baseGroup->setCheckable( false );
     baseGroup->setIcon( QgsApplication::style()->standardIcon( QStyle::SP_DirIcon ) );
     baseGroup->setToolTip( dir.path() );
     parentItem->appendRow( baseGroup );
-    createTree( baseGroup );
+    parentPaths << svgPaths.at( i );
+    mPathItemHash.insert( svgPaths.at( i ), baseGroup );
     QgsDebugMsg( QString( "SVG base path %1: %2" ).arg( i ).arg( baseGroup->data().toString() ) );
   }
+  mLoader->setParentPaths( parentPaths );
+  connect( mLoader, SIGNAL( foundPath( QString, QString ) ), this, SLOT( addPath( QString, QString ) ) );
+  mLoader->start();
 }
 
-void QgsSvgSelectorGroupsModel::createTree( QStandardItem* &parentGroup )
+QgsSvgSelectorGroupsModel::~QgsSvgSelectorGroupsModel()
 {
-  QDir parentDir( parentGroup->data().toString() );
-  Q_FOREACH ( const QString& item, parentDir.entryList( QDir::Dirs | QDir::NoDotAndDotDot ) )
-  {
-    QStandardItem* group = new QStandardItem( item );
-    group->setData( QVariant( parentDir.path() + '/' + item ) );
-    group->setEditable( false );
-    group->setCheckable( false );
-    group->setToolTip( parentDir.path() + '/' + item );
-    group->setIcon( QgsApplication::style()->standardIcon( QStyle::SP_DirIcon ) );
-    parentGroup->appendRow( group );
-    createTree( group );
-  }
+  mLoader->stop();
+}
+
+void QgsSvgSelectorGroupsModel::addPath( const QString& parentPath, const QString& item )
+{
+  QStandardItem* parentGroup = mPathItemHash.value( parentPath );
+  if ( !parentGroup )
+    return;
+
+  QString fullPath = parentPath + '/' + item;
+  QStandardItem* group = new QStandardItem( item );
+  group->setData( QVariant( fullPath ) );
+  group->setEditable( false );
+  group->setCheckable( false );
+  group->setToolTip( fullPath );
+  group->setIcon( QgsApplication::style()->standardIcon( QStyle::SP_DirIcon ) );
+  parentGroup->appendRow( group );
+  mPathItemHash.insert( fullPath, group );
 }
 
 
@@ -250,11 +440,14 @@ void QgsSvgSelectorWidget::populateIcons( const QModelIndex& idx )
 {
   QString path = idx.data( Qt::UserRole + 1 ).toString();
 
+  QAbstractItemModel* oldModel = mImagesListView->model();
   QgsSvgSelectorListModel* m = new QgsSvgSelectorListModel( mImagesListView, path );
   mImagesListView->setModel( m );
+  delete oldModel; //explicitly delete old model to force any background threads to stop
 
   connect( mImagesListView->selectionModel(), SIGNAL( currentChanged( const QModelIndex&, const QModelIndex& ) ),
            this, SLOT( svgSelectionChanged( const QModelIndex& ) ) );
+
 }
 
 void QgsSvgSelectorWidget::on_mFilePushButton_clicked()
@@ -319,8 +512,10 @@ void QgsSvgSelectorWidget::populateList()
   }
 
   // Initally load the icons in the List view without any grouping
+  QAbstractItemModel* oldModel = mImagesListView->model();
   QgsSvgSelectorListModel* m = new QgsSvgSelectorListModel( mImagesListView );
   mImagesListView->setModel( m );
+  delete oldModel; //explicitly delete old model to force any background threads to stop
 }
 
 //-- QgsSvgSelectorDialog
@@ -357,3 +552,4 @@ QgsSvgSelectorDialog::~QgsSvgSelectorDialog()
   QSettings settings;
   settings.setValue( "/Windows/SvgSelectorDialog/geometry", saveGeometry() );
 }
+