Concurrently load thumbnail images, improving startup times

ArtModel.cpp

@@ -4,13 +4,21 @@
 #include <QFile>
 #include <QFileInfo>
 #include <QIcon>
-#include <QImage>
-#include <QJsonArray>
 #include <QJsonDocument>
 #include <QJsonObject>
 #include <QPixmap>
+#include <QtConcurrent>
 
 ArtModel::ArtModel(const QString& definitionDirectory, const QString& assetDirectory) : QAbstractTableModel() {
+	piecesFuture = new QFutureWatcher<ArtPiece>(this);
+	connect(piecesFuture, &QFutureWatcher<ArtPiece>::resultReadyAt, this, &ArtModel::pieceFinished);
+	connect(piecesFuture, &QFutureWatcher<ArtPiece>::finished, this, &ArtModel::finished);
+
+	struct PieceInformation {
+		QString definition;
+		QString asset;
+	};
+	QVector<PieceInformation> pieceList;
 	QDirIterator it(definitionDirectory);
 	while (it.hasNext()) {
 		QFileInfo info(it.next());
@@ -18,22 +26,26 @@ ArtModel::ArtModel(const QString& definitionDirectory, const QString& assetDirec
 			continue;
 		}
 
+		pieceList.push_back(PieceInformation{QString("%1/%2").arg(definitionDirectory).arg(info.baseName()), QString("%1/%2").arg(assetDirectory).arg(info.baseName())});
+
 		beginInsertRows(QModelIndex(), m_artPieces.size(), m_artPieces.size() + 1);
 
-		ArtPiece p;
-		loadData(p, QString("%1/%2").arg(definitionDirectory).arg(info.baseName()), QString("%1/%2").arg(assetDirectory).arg(info.baseName()));
-
-		m_artPieces.push_back(p);
+		m_artPieces.push_back(ArtPiece{});
 
 		endInsertRows();
 	}
 
-	std::sort(m_artPieces.begin(), m_artPieces.end(), [](ArtPiece& a, ArtPiece& b)
-			  {
-				  return a.date > b.date;
-			  });
+	std::function<ArtPiece(const PieceInformation& info)> loadPiece = [this](const PieceInformation& info) -> ArtPiece {
+		ArtPiece p;
+		loadData(p, info.definition, info.asset);
 
-	dataChanged(index(0, 0), index(m_artPieces.size(), 0));
+		p.image.load(p.filename);
+		p.thumbnail = QPixmap::fromImage(p.image).scaled(100, 100, Qt::AspectRatioMode::KeepAspectRatio).toImage();
+
+		return p;
+	};
+
+	piecesFuture->setFuture(QtConcurrent::mapped(pieceList, loadPiece));
 }
 
 int ArtModel::rowCount(const QModelIndex &parent) const {
@@ -65,10 +77,7 @@ QVariant ArtModel::data(const QModelIndex &index, int role) const {
 		switch(index.column()) {
 			case 1:
 			{
-				QImage image;
-				image.load(m_artPieces[index.row()].filename);
-
-				return QPixmap::fromImage(image).scaled(100, 100, Qt::AspectRatioMode::KeepAspectRatio);
+				return m_artPieces[index.row()].thumbnail;
 			}
 				break;
 			case 3:
@@ -113,7 +122,25 @@ void ArtModel::loadData(ArtPiece& piece, const QString& filename, const QString&
 		piece.date = QDate::fromString(artJson["date"].toString(), "yyyy");
 	}
 
+	if (artJson.object().contains("title")) {
+		piece.title = artJson.object()["title"].toString();
+	}
+
 	if(artJson.object().contains("alt_text")) {
 		piece.hasAltText = true;
 	}
-}
+}
+void ArtModel::pieceFinished(int row) {
+	m_artPieces[row] = piecesFuture->resultAt(row);
+
+	Q_EMIT dataChanged(index(row, 0), index(row + 1, 0));
+}
+
+void ArtModel::finished() {
+	std::sort(m_artPieces.begin(), m_artPieces.end(), [](ArtPiece& a, ArtPiece& b)
+			  {
+				  return a.date > b.date;
+			  });
+
+	Q_EMIT dataChanged(index(0, 0), index(m_artPieces.size(), 0));
+}

ArtModel.h

@@ -1,7 +1,9 @@
 #pragma once
 
 #include <QAbstractTableModel>
+#include <QImage>
 #include <QJsonObject>
+#include <QFutureWatcher>
 
 struct ArtPiece {
 	QString filename, jsonFilename;
@@ -9,6 +11,7 @@ struct ArtPiece {
 	QJsonObject object;
 
 	QDate date;
+	QImage image, thumbnail;
 
 	bool hasAltText = false;
 };
@@ -26,5 +29,10 @@ public:
 private:
 	void loadData(ArtPiece& piece, const QString& filename, const QString& assetFilename);
 
+	void pieceFinished(int index);
+	void finished();
+
+	QFutureWatcher<ArtPiece>* piecesFuture;
+
 	QList<ArtPiece> m_artPieces;
 };

CMakeLists.txt

@@ -10,6 +10,7 @@ find_package(Qt5 COMPONENTS
     Core
     Gui
     Widgets
+    Concurrent
     REQUIRED)
 
 add_executable(Redai main.cpp MainWindow.cpp MainWindow.h ArtModel.cpp ArtModel.h ArtDetailWindow.cpp ArtDetailWindow.h imagelabel.cpp imagelabel.h)
@@ -17,5 +18,6 @@ target_link_libraries(Redai
     Qt5::Core
     Qt5::Gui
     Qt5::Widgets
+    Qt5::Concurrent
     )