Optimization (basic structures)

PdfForQtLib/sources/pdfoptimizer.cpp

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+//    Copyright (C) 2020 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/>.
+
+#include "pdfoptimizer.h"
+
+namespace pdf
+{
+
+PDFOptimizer::PDFOptimizer(OptimizationFlags flags, QObject* parent) :
+    QObject(parent),
+    m_flags(flags)
+{
+
+}
+
+void PDFOptimizer::optimize()
+{
+    // Jakub Melka: We divide optimization into stages, each
+    // stage can consist from multiple passes.
+    constexpr auto stages = { OptimizationFlags(DereferenceSimpleObjects),
+                              OptimizationFlags(RemoveNullObjects),
+                              OptimizationFlags(RemoveUnusedObjects | MergeIdenticalObjects),
+                              OptimizationFlags(ShrinkObjectStorage),
+                              OptimizationFlags(RecompressFlateStreams) };
+
+    int stage = 1;
+
+    emit optimizationStarted();
+    for (OptimizationFlags flags : stages)
+    {
+        emit optimizationProgress(tr("Stage %1").arg(stage++));
+        OptimizationFlags currentSteps = flags & m_flags;
+
+        int passIndex = 1;
+
+        bool pass = true;
+        while (pass)
+        {
+            emit optimizationProgress(tr("Pass %1").arg(passIndex++));
+            pass = false;
+
+            if (currentSteps.testFlag(DereferenceSimpleObjects))
+            {
+                pass = performDereferenceSimpleObjects() || pass;
+            }
+            if (currentSteps.testFlag(RemoveNullObjects))
+            {
+                pass = performRemoveNullObjects() || pass;
+            }
+            if (currentSteps.testFlag(RemoveUnusedObjects))
+            {
+                pass = performRemoveUnusedObjects() || pass;
+            }
+            if (currentSteps.testFlag(MergeIdenticalObjects))
+            {
+                pass = performMergeIdenticalObjects() || pass;
+            }
+            if (currentSteps.testFlag(ShrinkObjectStorage))
+            {
+                pass = performShrinkObjectStorage() || pass;
+            }
+            if (currentSteps.testFlag(RecompressFlateStreams))
+            {
+                pass = performRecompressFlateStreams() || pass;
+            }
+        }
+    }
+    emit optimizationFinished();
+}
+
+PDFOptimizer::OptimizationFlags PDFOptimizer::getFlags() const
+{
+    return m_flags;
+}
+
+void PDFOptimizer::setFlags(OptimizationFlags flags)
+{
+    m_flags = flags;
+}
+
+bool PDFOptimizer::performDereferenceSimpleObjects()
+{
+    return false;
+}
+
+bool PDFOptimizer::performRemoveNullObjects()
+{
+    return false;
+}
+
+bool PDFOptimizer::performRemoveUnusedObjects()
+{
+    return false;
+}
+
+bool PDFOptimizer::performMergeIdenticalObjects()
+{
+    return false;
+}
+
+bool PDFOptimizer::performShrinkObjectStorage()
+{
+    return false;
+}
+
+bool PDFOptimizer::performRecompressFlateStreams()
+{
+    return false;
+}
+
+}   // namespace pdf