Changes: limit rendering of minimized applications to 5fps

RevBy: Stanislav, Michael Hasselmann

Changes: Minimized applications are not allowed to repaint more than
5 times per second. All paint events when beeing in the switcher
and invisible will be discarded.

The base is there to disable paiting completely also for invisible
foreground applications. It is not yet actived though as it would
eat the very first frames when an application is started.

2 files changed, 48 insertions, 1 deletions

diff --git a/src/corelib/widgets/mwindow.cpp b/src/corelib/widgets/mwindow.cpp
index 3f4c69f5..31cfd34e 100644
--- a/src/corelib/widgets/mwindow.cpp
+++ b/src/corelib/widgets/mwindow.cpp
@@ -76,6 +76,8 @@ MWindowPrivate::MWindowPrivate() :
     minimizedSoftwareSwitchItem("/meegotouch/debug/minimized_software_switch"),
 #endif
     minimizedSoftwareSwitch(false),
+    updateIsPending(false),
+    discardedPaintEvent(false),
     q_ptr(NULL)
 {
 #ifndef Q_WS_X11
@@ -88,6 +90,8 @@ MWindowPrivate::MWindowPrivate() :
         angle = window->orientationAngle();
     else
         angle = MOrientationTracker::instance()->orientationAngle();
+
+    timeSinceLastPaintInSwitcher.invalidate();
 }
 
 MWindowPrivate::~MWindowPrivate()
@@ -386,6 +390,13 @@ void MWindowPrivate::doEnterDisplayEvent()
 
     q->enterDisplayEvent();
     emit q->displayEntered();
+
+    if (discardedPaintEvent) {
+        // we discarded a paint event while beeing invisible
+        // make sure the screen is up to date
+        discardedPaintEvent = false;
+        QTimer::singleShot(0, q->viewport(), SLOT(update()));
+    }
 }
 
 void MWindowPrivate::doExitDisplayEvent()
@@ -442,6 +453,7 @@ void MWindowPrivate::windowStateChangeEvent(QWindowStateChangeEvent *event)
     else if (event->oldState() == Qt::WindowMinimized &&
              q->windowState() != Qt::WindowMinimized) {
         isInSwitcher = false;
+        timeSinceLastPaintInSwitcher.invalidate();
         emit q->switcherExited();
     }
 
@@ -943,14 +955,44 @@ void MWindow::onDisplayChangeEvent(MOnDisplayChangeEvent *event)
 
 void MWindow::paintEvent(QPaintEvent *event)
 {
-#ifdef M_USE_OPENGL
     Q_D(MWindow);
+#ifdef M_USE_OPENGL
 
     if (!MApplication::softwareRendering()) {
         MGLES2Renderer::activate(d->glWidget);
     }
 #endif // M_USE_OPENGL
 
+    if (isInSwitcher()) {
+        if (!isOnDisplay()) {
+            // TODO: also do this check for the foreground app not visible in the switcher once onDisplay is immediately
+            // true when starting an application. right now during startup the first frames would be discarded
+            mWarning("MWindow::paintEvent") << "Application is not visible. Paint event discarded. Make sure the application does not paint in the first place.";
+            event->accept();
+            d->discardedPaintEvent = true;
+            return;
+        } else if (!d->timeSinceLastPaintInSwitcher.isValid()) {
+            d->timeSinceLastPaintInSwitcher.start();
+            d->updateIsPending = false;
+        } else {
+            const int maxFpsInSwitcher = 5;
+            const int minDelay = 1000. / maxFpsInSwitcher;
+            qint64 msSinceLastPaint = d->timeSinceLastPaintInSwitcher.elapsed();
+            if (msSinceLastPaint < minDelay) {
+                event->accept();
+                if (!d->updateIsPending) {
+                    // trigger a new paint event as otherwise the screen may not be up to date
+                    QTimer::singleShot(minDelay, viewport(), SLOT(update()));
+                    d->updateIsPending = true;
+                }
+                return;
+            } else {
+                d->timeSinceLastPaintInSwitcher.restart();
+                d->updateIsPending = false;
+            }
+        }
+    }
+
     QGraphicsView::paintEvent(event);
 }
 
diff --git a/src/corelib/widgets/mwindow_p.h b/src/corelib/widgets/mwindow_p.h
index 7e190d10..eaa04e36 100644
--- a/src/corelib/widgets/mwindow_p.h
+++ b/src/corelib/widgets/mwindow_p.h
@@ -21,6 +21,7 @@
 #define MWINDOW_P_H
 
 #include <QTimeLine>
+#include <QElapsedTimer>
 #include "mwindow.h"
 
 #include <mscenemanager.h>
@@ -98,6 +99,10 @@ public:
 #endif
     bool minimizedSoftwareSwitch;
 
+    QElapsedTimer timeSinceLastPaintInSwitcher;
+    bool updateIsPending;
+    bool discardedPaintEvent;
+
 protected:
     MWindow *q_ptr;
 private: