uikit: Deliver update requests via CADisplayLink callback

Improves performance over the default timer-implementation, and allows
us to control the rate and paused state of the display link.

Change-Id: I05761b6eb48f5e91af35735e2faa477427cd8440
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/plugins/platforms/ios/qiosscreen.h

@@ -65,9 +65,13 @@ public:
     UIScreen *uiScreen() const;
     UIWindow *uiWindow() const;
 
+    void setUpdatesPaused(bool);
+
     void updateProperties();
 
 private:
+    void deliverUpdateRequests() const;
+
     UIScreen *m_uiScreen;
     UIWindow *m_uiWindow;
     QRect m_geometry;
@@ -76,6 +80,7 @@ private:
     uint m_physicalDpi;
     QSizeF m_physicalSize;
     QIOSOrientationListener *m_orientationListener;
+    CADisplayLink *m_displayLink;
 };
 
 QT_END_NAMESPACE

src/plugins/platforms/ios/qiosscreen.mm

@@ -40,8 +40,31 @@
 #include "qiosviewcontroller.h"
 #include "quiview.h"
 
+#include <QtGui/private/qwindow_p.h>
+
 #include <sys/sysctl.h>
 
+// -------------------------------------------------------------------------
+
+typedef void (^DisplayLinkBlock)(CADisplayLink *displayLink);
+
+@implementation UIScreen (DisplayLinkBlock)
+- (CADisplayLink*)displayLinkWithBlock:(DisplayLinkBlock)block
+{
+    return [self displayLinkWithTarget:[[block copy] autorelease]
+        selector:@selector(invokeDisplayLinkBlock:)];
+}
+@end
+
+@implementation NSObject (DisplayLinkBlock)
+- (void)invokeDisplayLinkBlock:(CADisplayLink *)sender
+{
+    DisplayLinkBlock block = static_cast<id>(self);
+    block(sender);
+}
+@end
+
+
 // -------------------------------------------------------------------------
 
 static QIOSScreen* qtPlatformScreenFor(UIScreen *uiScreen)
@@ -208,10 +231,16 @@ QIOSScreen::QIOSScreen(UIScreen *screen)
     }
 
     updateProperties();
+
+    m_displayLink = [m_uiScreen displayLinkWithBlock:^(CADisplayLink *) { deliverUpdateRequests(); }];
+    m_displayLink.paused = YES; // Enabled when clients call QWindow::requestUpdate()
+    [m_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
 }
 
 QIOSScreen::~QIOSScreen()
 {
+    [m_displayLink invalidate];
+
     [m_orientationListener release];
     [m_uiWindow release];
 }
@@ -291,6 +320,35 @@ void QIOSScreen::updateProperties()
         QWindowSystemInterface::handleScreenGeometryChange(screen(), m_geometry, m_availableGeometry);
 }
 
+void QIOSScreen::setUpdatesPaused(bool paused)
+{
+    m_displayLink.paused = paused;
+}
+
+void QIOSScreen::deliverUpdateRequests() const
+{
+    bool pauseUpdates = true;
+
+    QList<QWindow*> windows = QGuiApplication::allWindows();
+    for (int i = 0; i < windows.size(); ++i) {
+        if (platformScreenForWindow(windows.at(i)) != this)
+            continue;
+
+        QWindowPrivate *wp = static_cast<QWindowPrivate *>(QObjectPrivate::get(windows.at(i)));
+        if (!wp->updateRequestPending)
+            continue;
+
+        wp->deliverUpdateRequest();
+
+        // Another update request was triggered, keep the display link running
+        if (wp->updateRequestPending)
+            pauseUpdates = false;
+    }
+
+    // Pause the display link if there are no pending update requests
+    m_displayLink.paused = pauseUpdates;
+}
+
 QRect QIOSScreen::geometry() const
 {
     return m_geometry;

src/plugins/platforms/ios/qioswindow.h

@@ -82,6 +82,8 @@ public:
 
     QSurfaceFormat format() const Q_DECL_OVERRIDE;
 
+    void requestUpdate() Q_DECL_OVERRIDE;
+
 private:
     void applicationStateChanged(Qt::ApplicationState state);
     void applyGeometry(const QRect &rect);

src/plugins/platforms/ios/qioswindow.mm

@@ -371,6 +371,11 @@ void QIOSWindow::clearAccessibleCache()
     [m_view clearAccessibleCache];
 }
 
+void QIOSWindow::requestUpdate()
+{
+    static_cast<QIOSScreen *>(screen())->setUpdatesPaused(false);
+}
+
 #include "moc_qioswindow.cpp"
 
 QT_END_NAMESPACE