Scale artist images in a background thread

src/songinfo/songinfobase.cpp

@@ -43,7 +43,7 @@ SongInfoBase::SongInfoBase(QWidget* parent)
   // Add a container widget to the scroll area
   QWidget* container_widget = new QWidget;
   container_widget->setLayout(container_);
-  container_widget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::MinimumExpanding);
+  container_widget->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Minimum);
   container_widget->setBackgroundRole(QPalette::Base);
   container_->setSizeConstraint(QLayout::SetMinAndMaxSize);
   container_->setContentsMargins(0, 0, 0, 0);
@@ -52,7 +52,7 @@ SongInfoBase::SongInfoBase(QWidget* parent)
   scroll_area_->setWidgetResizable(true);
 
   // Add a spacer to the bottom of the container
-  container_->addSpacerItem(new QSpacerItem(0, 0, QSizePolicy::Fixed, QSizePolicy::Expanding));
+  container_->addStretch();
 
   // Set stylesheet
   QFile stylesheet(":/songinfo.css");

src/widgets/prettyimage.cpp

@@ -23,12 +23,15 @@
 #include <QDesktopWidget>
 #include <QDir>
 #include <QFileDialog>
+#include <QFuture>
+#include <QFutureWatcher>
 #include <QLabel>
 #include <QMenu>
 #include <QNetworkReply>
 #include <QPainter>
 #include <QScrollArea>
 #include <QSettings>
+#include <QtConcurrentRun>
 
 const int PrettyImage::kTotalHeight = 200;
 const int PrettyImage::kReflectionHeight = 40;
@@ -58,7 +61,7 @@ void PrettyImage::LazyLoad() {
   // Start fetching the image
   QNetworkReply* reply = network_->get(QNetworkRequest(url_));
   connect(reply, SIGNAL(finished()), SLOT(ImageFetched()));
-  state_ = State_Loading;
+  state_ = State_Fetching;
 }
 
 QSize PrettyImage::image_size() const {
@@ -82,17 +85,32 @@ void PrettyImage::ImageFetched() {
   if (image.isNull()) {
     deleteLater();
   } else {
-    state_ = State_Finished;
+    state_ = State_CreatingThumbnail;
     image_ = image;
-    thumbnail_ = QPixmap::fromImage(image_.scaledToHeight(
-        kImageHeight, Qt::SmoothTransformation));
 
-    updateGeometry();
-    update();
-    emit Loaded();
+    QFuture<QImage> future = QtConcurrent::run(image_,
+        &QImage::scaledToHeight, kImageHeight, Qt::SmoothTransformation);
+
+    QFutureWatcher<QImage>* watcher = new QFutureWatcher<QImage>(this);
+    watcher->setFuture(future);
+    connect(watcher, SIGNAL(finished()), SLOT(ImageScaled()));
   }
 }
 
+void PrettyImage::ImageScaled() {
+  QFutureWatcher<QImage>* watcher = reinterpret_cast<QFutureWatcher<QImage>*>(sender());
+  if (!watcher)
+    return;
+  watcher->deleteLater();
+
+  thumbnail_ = QPixmap::fromImage(watcher->result());
+  state_ = State_Finished;
+
+  updateGeometry();
+  update();
+  emit Loaded();
+}
+
 void PrettyImage::paintEvent(QPaintEvent* ) {
   // Draw at the bottom of our area
   QRect image_rect(QPoint(0, 0), image_size());
@@ -142,7 +160,8 @@ void PrettyImage::paintEvent(QPaintEvent* ) {
 void PrettyImage::DrawThumbnail(QPainter* p, const QRect& rect) {
   switch (state_) {
   case State_WaitingForLazyLoad:
-  case State_Loading:
+  case State_Fetching:
+  case State_CreatingThumbnail:
     p->setPen(palette().color(QPalette::Disabled, QPalette::Text));
     p->drawText(rect, Qt::AlignHCenter | Qt::AlignBottom, tr("Loading..."));
     break;

src/widgets/prettyimage.h

@@ -56,11 +56,13 @@ protected:
 
 private slots:
   void ImageFetched();
+  void ImageScaled();
 
 private:
   enum State {
     State_WaitingForLazyLoad,
-    State_Loading,
+    State_Fetching,
+    State_CreatingThumbnail,
     State_Finished,
   };