Asynchronous page rendering (compilig of pages)

PdfForQtLib/sources/pdfcompiler.h

@@ -0,0 +1,92 @@
+//    Copyright (C) 2019 Jakub Melka
+//
+//    This file is part of PdfForQt.
+//
+//    PdfForQt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    PdfForQt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.
+
+#ifndef PDFCOMPILER_H
+#define PDFCOMPILER_H
+
+#include "pdfrenderer.h"
+#include "pdfpainter.h"
+
+#include <QCache>
+#include <QFuture>
+#include <QFutureWatcher>
+
+namespace pdf
+{
+class PDFDrawWidgetProxy;
+
+/// Asynchronous page compiler compiles pages asynchronously, and stores them in the
+/// cache. Cache size can be set. This object is designed to cooperate with
+/// draw widget proxy.
+class PDFAsynchronousPageCompiler : public QObject
+{
+    Q_OBJECT
+
+private:
+    using BaseClass = QObject;
+
+public:
+    explicit PDFAsynchronousPageCompiler(PDFDrawWidgetProxy* proxy);
+
+    /// Starts the engine. Call this function only if the engine
+    /// is stopped.
+    void start();
+
+    /// Stops the engine and all underlying asynchronous tasks. Also
+    /// clears the cache. Call this function only if engine is active.
+    void stop();
+
+    /// Resets the engine - calls stop and then calls start.
+    void reset();
+
+    enum class State
+    {
+        Inactive,
+        Active,
+        Stopping
+    };
+
+    /// Tries to retrieve precompiled page from the cache. If page is not found,
+    /// then nullptr is returned (no exception is thrown). If \p compile is set to true,
+    /// and page is not found, and compiler is active, then new asynchronous compile
+    /// task is performed.
+    /// \param pageIndex Index of page
+    /// \param compile Compile the page, if it is not found in the cache
+    const PDFPrecompiledPage* getPrecompiledCache(PDFInteger pageIndex, bool compile);
+
+signals:
+    void pageImageChanged(bool all, const std::vector<PDFInteger>& pages);
+    void renderingError(PDFInteger pageIndex, const QList<PDFRenderError>& errors);
+
+private:
+    void onPageCompiled();
+
+    struct CompileTask
+    {
+        QFuture<PDFPrecompiledPage> taskFuture;
+        QFutureWatcher<PDFPrecompiledPage>* taskWatcher = nullptr;
+    };
+
+    PDFDrawWidgetProxy* m_proxy;
+    State m_state = State::Inactive;
+    QCache<PDFInteger, PDFPrecompiledPage> m_cache;
+    std::map<PDFInteger, CompileTask> m_tasks;
+};
+
+}   // namespace pdf
+
+#endif // PDFCOMPILER_H