[hwcomposer] Add support for vsync

Note: qt5-qpa-hwcomposer-plugin does the vsync in a different way:
it uses a wait condition to truly block in present till the vsync.
Maybe we need to do that as well.

backends/hwcomposer/egl_hwcomposer_backend.cpp

@@ -35,6 +35,7 @@ EglHwcomposerBackend::EglHwcomposerBackend(HwcomposerBackend *backend)
     init();
     // EGL is always direct rendering
     setIsDirectRendering(true);
+    setSyncsToVBlank(true);
 }
 
 EglHwcomposerBackend::~EglHwcomposerBackend()

backends/hwcomposer/hwcomposer_backend.cpp

@@ -110,6 +110,28 @@ void HwcomposerBackend::init()
 
     // unblank, setPowerMode?
     m_device = hwcDevice;
+
+    // register callbacks
+    hwc_procs_t *procs = new hwc_procs_t;
+    procs->invalidate = [] (const struct hwc_procs* procs) {
+        Q_UNUSED(procs)
+    };
+    procs->vsync = [] (const struct hwc_procs* procs, int disp, int64_t timestamp) {
+        Q_UNUSED(procs)
+        if (disp != 0) {
+            return;
+        }
+        QMetaObject::invokeMethod(dynamic_cast<HwcomposerBackend*>(waylandServer()->backend()),
+                                  "vsync",
+                                  Qt::QueuedConnection);
+    };
+    procs->hotplug = [] (const struct hwc_procs* procs, int disp, int connected) {
+        Q_UNUSED(procs)
+        Q_UNUSED(disp)
+        Q_UNUSED(connected)
+    };
+    m_device->registerProcs(m_device, procs);
+
     toggleBlankOutput();
 
     // get display configuration
@@ -136,6 +158,7 @@ void HwcomposerBackend::toggleBlankOutput()
     }
     m_outputBlank = !m_outputBlank;
     m_device->blank(m_device, 0, m_outputBlank ? 1 : 0);
+    m_device->eventControl(m_device, 0, HWC_EVENT_VSYNC, m_outputBlank ? 0 : 1);
     // enable/disable compositor repainting when blanked
     if (Compositor *compositor = Compositor::self()) {
         if (m_outputBlank) {
@@ -162,6 +185,27 @@ OpenGLBackend *HwcomposerBackend::createOpenGLBackend()
     return new EglHwcomposerBackend(this);
 }
 
+void HwcomposerBackend::present()
+{
+    if (m_pageFlipPending) {
+        return;
+    }
+    m_pageFlipPending = true;
+    if (Compositor::self()) {
+        Compositor::self()->aboutToSwapBuffers();
+    }
+}
+
+void HwcomposerBackend::vsync()
+{
+    if (m_pageFlipPending) {
+        m_pageFlipPending = false;
+        if (Compositor::self()) {
+            Compositor::self()->bufferSwapComplete();
+        }
+    }
+}
+
 static void initLayer(hwc_layer_1_t *layer, const hwc_rect_t &rect)
 {
     memset(layer, 0, sizeof(hwc_layer_1_t));
@@ -217,6 +261,7 @@ HwcomposerWindow::~HwcomposerWindow()
 
 void HwcomposerWindow::present(HWComposerNativeWindowBuffer *buffer)
 {
+    m_backend->present();
     hwc_composer_device_1_t *device = m_backend->device();
 
     auto fblayer = &m_list[0]->hwLayers[1];
@@ -235,6 +280,7 @@ void HwcomposerWindow::present(HWComposerNativeWindowBuffer *buffer)
         close(m_list[0]->retireFenceFd);
         m_list[0]->retireFenceFd = -1;
     }
+    m_list[0]->flags = 0;
 }
 
 }

backends/hwcomposer/hwcomposer_backend.h

@@ -59,10 +59,14 @@ public:
     hwc_composer_device_1_t *device() const {
         return m_device;
     }
+    void present();
     int refreshRate() const {
         return m_refreshRate;
     }
 
+public Q_SLOTS:
+    void vsync();
+
 private Q_SLOTS:
     void toggleBlankOutput();
 
@@ -70,6 +74,7 @@ private:
     QSize m_displaySize;
     hwc_composer_device_1_t *m_device = nullptr;
     bool m_outputBlank = true;
+    bool m_pageFlipPending = false;
     int m_refreshRate = 60000;
 };