pdfviewer example: add threaded PageCache

thread fixes

7 files changed, 172 insertions, 35 deletions

diff --git a/examples/widgets/pdfviewer/images/busy.png b/examples/widgets/pdfviewer/images/busy.png
new file mode 100644
index 0000000..69056c4
--- /dev/null
+++ b/examples/widgets/pdfviewer/images/busy.png
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;
+    }
+}
diff --git a/examples/widgets/pdfviewer/pagecache.h b/examples/widgets/pdfviewer/pagecache.h
new file mode 100644
index 0000000..49d8bf8
--- /dev/null
+++ b/examples/widgets/pdfviewer/pagecache.h
@@ -0,0 +1,46 @@
+#ifndef PAGECACHE_H
+#define PAGECACHE_H
+
+#include <QBrush>
+#include <QHash>
+#include <QPixmap>
+#include <QRunnable>
+
+class QPdfDocument;
+
+class PageCache : public QObject
+{
+    Q_OBJECT
+public:
+    PageCache(QPdfDocument *doc, qreal zoom);
+    ~PageCache();
+
+    QPixmap get(int page);
+
+public slots:
+    void run();
+
+signals:
+    void pagesNeeded();
+    void pageReady(int page);
+
+private:
+    void insertPage(int page);
+
+private:
+    QThread *m_thread;
+    QPdfDocument *m_doc;
+    QHash<int, QPixmap> m_pageCache;
+    qreal m_zoom;
+    int m_lastPageRequested;
+    QPixmap m_placeholderIcon;
+    QBrush m_placeholderBackground;
+
+    // performance statistics
+    qreal m_minRenderTime;
+    qreal m_maxRenderTime;
+    qreal m_totalRenderTime;
+    int m_totalPagesRendered;
+};
+
+#endif // PAGECACHE_H
diff --git a/examples/widgets/pdfviewer/pdfviewer.pro b/examples/widgets/pdfviewer/pdfviewer.pro
index babcd85..4056915 100644
--- a/examples/widgets/pdfviewer/pdfviewer.pro
+++ b/examples/widgets/pdfviewer/pdfviewer.pro
@@ -4,10 +4,12 @@ TEMPLATE = app
 
 SOURCES += main.cpp\
         mainwindow.cpp \
-    sequentialpagewidget.cpp
+    sequentialpagewidget.cpp \
+    pagecache.cpp
 
 HEADERS  += mainwindow.h \
-    sequentialpagewidget.h
+    sequentialpagewidget.h \
+    pagecache.h
 
 FORMS    += mainwindow.ui
 
diff --git a/examples/widgets/pdfviewer/resources.qrc b/examples/widgets/pdfviewer/resources.qrc
index 945c595..02d9655 100644
--- a/examples/widgets/pdfviewer/resources.qrc
+++ b/examples/widgets/pdfviewer/resources.qrc
@@ -7,5 +7,6 @@
         <file>images/zoom-in-32.png</file>
         <file>images/zoom-out-24.png</file>
         <file>images/zoom-out-32.png</file>
+        <file>images/busy.png</file>
     </qresource>
 </RCC>
diff --git a/examples/widgets/pdfviewer/sequentialpagewidget.cpp b/examples/widgets/pdfviewer/sequentialpagewidget.cpp
index 5bac32c..6b84015 100644
--- a/examples/widgets/pdfviewer/sequentialpagewidget.cpp
+++ b/examples/widgets/pdfviewer/sequentialpagewidget.cpp
@@ -1,4 +1,5 @@
 #include "sequentialpagewidget.h"
+#include "pagecache.h"
 #include <QPaintEvent>
 #include <QPainter>
 #include <QPdfDocument>
@@ -12,15 +13,12 @@ Q_DECLARE_LOGGING_CATEGORY(lcExample)
 SequentialPageWidget::SequentialPageWidget(QWidget *parent)
     : QWidget(parent)
     , m_doc(Q_NULLPTR)
+    , m_pageCache(Q_NULLPTR)
     , m_background(Qt::darkGray)
     , m_pageSpacing(3)
     , m_topPageShowing(0)
     , m_zoom(1.)
     , m_screenResolution(QGuiApplication::primaryScreen()->logicalDotsPerInch() / 72.0)
-    , m_minRenderTime(1000000000.)
-    , m_maxRenderTime(0.)
-    , m_totalRenderTime(0.)
-    , m_totalPagesRendered(0)
 {
 }
 
@@ -32,6 +30,10 @@ void SequentialPageWidget::setDocument(QPdfDocument *doc)
 {
     m_doc = doc;
     m_topPageShowing = 0;
+    if (m_pageCache)
+        delete m_pageCache;
+    m_pageCache = new PageCache(doc, m_screenResolution * m_zoom);
+    connect(m_pageCache, SIGNAL(pageReady(int)), this, SLOT(update()));
     invalidate();
 }
 
@@ -49,7 +51,11 @@ QSizeF SequentialPageWidget::pageSize(int page)
 
 void SequentialPageWidget::invalidate()
 {
-    m_pageCache.clear();
+    if (m_pageCache)
+        delete m_pageCache;
+    if (m_doc)
+        m_pageCache = new PageCache(m_doc, m_screenResolution * m_zoom);
+    connect(m_pageCache, SIGNAL(pageReady(int)), this, SLOT(update()));
     QSizeF totalSize(0, m_pageSpacing);
     for (int page = 0; page < m_doc->pageCount(); ++page) {
         QSizeF size = pageSize(page);
@@ -88,36 +94,17 @@ void SequentialPageWidget::paintEvent(QPaintEvent * event)
     }
     y += m_pageSpacing;
     m_topPageShowing = page;
-    int previousRendered = m_totalPagesRendered;
+    if (!m_pageCache) return;
 
     // Actually render pages
     while (y < event->rect().bottom() && page < m_doc->pageCount()) {
-        if (!m_pageCache.contains(page)) {
-            QSizeF size = pageSize(page);
-            qCDebug(lcExample) << "rendering page" << page << "to size" << size;
-            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));
-        }
-        const QPixmap &pm = m_pageCache[page];
+        const QPixmap &pm = m_pageCache->get(page);
         painter.drawPixmap((width() - pm.width()) / 2, y, pm);
         y += pm.height() + m_pageSpacing;
         ++page;
     }
     m_bottomPageShowing = page - 1;
     emit showingPageRange(m_topPageShowing, m_bottomPageShowing);
-
-    if (m_totalPagesRendered != previousRendered)
-        qCDebug(lcExample) << "rendering time: min" << m_minRenderTime <<
-                              "avg" << m_totalRenderTime / m_totalPagesRendered <<
-                              "max" << m_maxRenderTime;
 }
 
 qreal SequentialPageWidget::yForPage(int endPage)
diff --git a/examples/widgets/pdfviewer/sequentialpagewidget.h b/examples/widgets/pdfviewer/sequentialpagewidget.h
index 3d91279..23dfe7f 100644
--- a/examples/widgets/pdfviewer/sequentialpagewidget.h
+++ b/examples/widgets/pdfviewer/sequentialpagewidget.h
@@ -4,6 +4,7 @@
 #include <QWidget>
 
 class QPdfDocument;
+class PageCache;
 
 class SequentialPageWidget : public QWidget
 {
@@ -33,7 +34,7 @@ private:
 
 private:
     QPdfDocument *m_doc;
-    QHash<int, QPixmap> m_pageCache;
+    PageCache *m_pageCache;
     QBrush m_background;
     int m_pageSpacing;
     int m_topPageShowing;
@@ -41,12 +42,6 @@ private:
     QSize m_totalSize;
     qreal m_zoom;
     qreal m_screenResolution; // pixels per point
-
-    // performance statistics
-    qreal m_minRenderTime;
-    qreal m_maxRenderTime;
-    qreal m_totalRenderTime;
-    int m_totalPagesRendered;
 };
 
 #endif // SEQUENTIALPAGEWIDGET_H