1 files changed, 106 insertions, 0 deletions
diff --git a/examples/widgets/pdfviewer/pagecache.cpp b/examples/widgets/pdfviewer/pagecache.cpp
new file mode 100644
index 0000000..5943b90
--- /dev/null
+++ b/examples/widgets/pdfviewer/pagecache.cpp
@@ -0,0 +1,106 @@
+#include "pagecache.h"
+#include <QPainter>
+#include <QPdfDocument>
+#include <QLoggingCategory>
+#include <QElapsedTimer>
+#include <QThread>
+
+Q_DECLARE_LOGGING_CATEGORY(lcExample)
+
+PageCache::PageCache(QPdfDocument *doc, qreal zoom)
+    : QObject(Q_NULLPTR)
+    , m_thread(new QThread(this))
+    , m_doc(doc)
+    , m_zoom(zoom)
+    , m_placeholderIcon(":icons/images/busy.png")
+    , m_placeholderBackground(Qt::white)
+    , m_minRenderTime(1000000000.)
+    , m_maxRenderTime(0.)
+    , m_totalRenderTime(0.)
+    , m_totalPagesRendered(0)
+{
+    moveToThread(m_thread);
+    connect(this, &PageCache::pagesNeeded, this, &PageCache::run, Qt::QueuedConnection);
+}
+
+PageCache::~PageCache()
+{
+}
+
+/*!
+   Get the result from the cache,
+   or a placeholder pixmap if unavailable.
+ */
+QPixmap PageCache::get(int page)
+{
+    m_lastPageRequested = page;
+    if (m_pageCache.contains(page))
+        return m_pageCache[page];
+    if (!m_thread->isRunning())
+        m_thread->start(QThread::LowestPriority);
+    emit pagesNeeded();
+    QSizeF sizeF = m_doc->pageSize(page);
+    if (!sizeF.isValid())
+        return QPixmap();
+    QSize size = QSizeF(sizeF * m_zoom).toSize();
+    QPixmap placeholder(size);
+    {
+        QPainter painter(&placeholder);
+        painter.fillRect(QRect(QPoint(), size), m_placeholderBackground);
+        painter.drawPixmap((size.width() - m_placeholderIcon.width()) / 2,
+            (size.height() - m_placeholderIcon.height()) / 2, m_placeholderIcon);
+    }
+    return placeholder;
+}
+
+void PageCache::run()
+{
+    int lastPageRequested = m_lastPageRequested;
+    int forward = lastPageRequested;
+    int backward = lastPageRequested - 1;
+    while (true) {
+        bool done = true;
+        if (lastPageRequested != m_lastPageRequested) {
+            lastPageRequested = m_lastPageRequested;
+            forward = lastPageRequested;
+            backward = lastPageRequested - 1;
+        }
+        if (forward < m_doc->pageCount()) {
+            if (!m_pageCache.contains(forward))
+                insertPage(forward);
+            done = false;
+        }
+        if (backward >= 0) {
+            if (!m_pageCache.contains(backward))
+                insertPage(backward);
+            done = false;
+        }
+        ++forward;
+        --backward;
+        if (done)
+            return;
+    }
+}
+
+void PageCache::insertPage(int page)
+{
+    if (!m_pageCache.contains(page)) {
+        QSizeF size = m_doc->pageSize(page) * m_zoom;
+        QElapsedTimer timer; timer.start();
+        const QImage &img = m_doc->render(page, size);
+        qreal secs = timer.nsecsElapsed() / 1000000000.0;
+        if (secs < m_minRenderTime)
+            m_minRenderTime = secs;
+        if (secs > m_maxRenderTime)
+            m_maxRenderTime = secs;
+        m_totalRenderTime += secs;
+        ++m_totalPagesRendered;
+        m_pageCache.insert(page, QPixmap::fromImage(img));
+        emit pageReady(page);
+
+        qCDebug(lcExample) << "page" << page << "zoom" << m_zoom << "size" << size << "in" << secs <<
+                              "secs; min" << m_minRenderTime <<
+                              "avg" << m_totalRenderTime / m_totalPagesRendered <<
+                              "max" << m_maxRenderTime;
+    }
+}