PlatformSurfaceFilter/Renderer: render only when surface is exposed

Change-Id: Idec2f0ee5f3ace590421698293742932e8843aae
Reviewed-by: Andy Nichols <andy.nichols@theqtcompany.com>

3 files changed, 19 insertions, 2 deletions

diff --git a/src/render/backend/platformsurfacefilter.cpp b/src/render/backend/platformsurfacefilter.cpp
index 6e7e1a21c..248e54d93 100644
--- a/src/render/backend/platformsurfacefilter.cpp
+++ b/src/render/backend/platformsurfacefilter.cpp
@@ -95,6 +95,11 @@ bool PlatformSurfaceFilter::eventFilter(QObject *obj, QEvent *e)
             Q_UNREACHABLE();
         }
     }
+
+    if (obj == m_obj && e->type() == QEvent::Expose) {
+        QExposeEvent *ev = static_cast<QExposeEvent *>(e);
+        m_renderer->setSurfaceExposed(!ev->region().isEmpty());
+    }
     return false;
 }
 
diff --git a/src/render/backend/renderer.cpp b/src/render/backend/renderer.cpp
index 5ad77b19d..73d0b453e 100644
--- a/src/render/backend/renderer.cpp
+++ b/src/render/backend/renderer.cpp
@@ -143,6 +143,7 @@ Renderer::Renderer(QRenderAspect::RenderType type)
     , m_vsyncFrameAdvanceService(new VSyncFrameAdvanceService())
     , m_debugLogger(Q_NULLPTR)
     , m_pickEventFilter(new PickEventFilter())
+    , m_exposed(0)
 {
     // Set renderer as running - it will wait in the context of the
     // RenderThread for RenderViews to be submitted
@@ -332,7 +333,6 @@ void Renderer::initialize(QOpenGLContext *context)
     if (enableDebugLogging)
         sf.setOption(QSurfaceFormat::DebugContext);
 
-
     QOpenGLContext* ctx = context ? context : new QOpenGLContext;
     if (!context) {
         qCDebug(Backend) << "Creating OpenGL context with format" << sf;
@@ -395,6 +395,12 @@ void Renderer::shutdown()
     }
 }
 
+void Renderer::setSurfaceExposed(bool exposed)
+{
+    qCDebug(Backend) << "Window exposed: " << exposed;
+    m_exposed.fetchAndStoreOrdered(exposed);
+}
+
 void Renderer::setFrameGraphRoot(const Qt3DCore::QNodeId &frameGraphRootUuid)
 {
     m_frameGraphRootUuid = frameGraphRootUuid;
@@ -526,7 +532,10 @@ void Renderer::render()
     // One framegraph description
 
     while (m_running.load() > 0) {
-        doRender();
+        if (m_exposed.load() > 0)
+            doRender();
+        else
+            QThread::msleep(250);
     }
 }
 
diff --git a/src/render/backend/renderer_p.h b/src/render/backend/renderer_p.h
index 7118f9ff1..1df435595 100644
--- a/src/render/backend/renderer_p.h
+++ b/src/render/backend/renderer_p.h
@@ -174,6 +174,8 @@ public:
     QMutex* mutex() { return &m_mutex; }
     bool isRunning() const { return m_running.load(); }
 
+    void setSurfaceExposed(bool exposed);
+
 #ifdef QT3D_RENDER_UNIT_TESTS
 public:
 #else
@@ -239,6 +241,7 @@ private:
 
     QVector<Attribute *> m_dirtyAttributes;
     QVector<Geometry *> m_dirtyGeometry;
+    QAtomicInt m_exposed;
 };
 
 } // namespace Render