QtWidgets: Improve native and top-level OpenGL widget performance

Since 7c6625b105511191f739d07dc658094ff6f682ac native OpenGL widgets
are able to render, but performance is very low.  It also slows down
rendering for top-level OpenGL widgets.

Render-to-texture widgets prevent triggering unnecessary backingstore
painting when only the OpenGL content changes.
This patch makes possible to use that feature for native and top-level
widgets by calling "markDirtyOnScreen()" function only when necessary.

This patch also prevents native and top-level OpenGL widgets from
flickering during resizing.

Task-number: QTBUG-50381
Task-number: QTBUG-49620
Change-Id: I0c16ea644fb869a00772fd74e1709611e627bff3
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

1 files changed, 15 insertions, 11 deletions

diff --git a/src/widgets/kernel/qwidgetbackingstore.cpp b/src/widgets/kernel/qwidgetbackingstore.cpp
index 3f7f9291b6..d9d1c887c1 100644
--- a/src/widgets/kernel/qwidgetbackingstore.cpp
+++ b/src/widgets/kernel/qwidgetbackingstore.cpp
@@ -1079,7 +1079,8 @@ void QWidgetBackingStore::sync(QWidget *exposedWidget, const QRegion &exposedReg
 
     // Nothing to repaint.
     if (!isDirty() && store->size().isValid()) {
-        qt_flush(exposedWidget, exposedRegion, store, tlw, tlwOffset, widgetTexturesFor(tlw, tlw), this);
+        QPlatformTextureList *tl = widgetTexturesFor(tlw, exposedWidget);
+        qt_flush(exposedWidget, tl ? QRegion() : exposedRegion, store, tlw, tlwOffset, tl, this);
         return;
     }
 
@@ -1250,9 +1251,17 @@ void QWidgetBackingStore::doSync()
         for (int i = 0; i < paintPending.count(); ++i) {
             QWidget *w = paintPending[i];
             w->d_func()->sendPaintEvent(w->rect());
-            QWidget *npw = w->nativeParentWidget();
-            if (w->internalWinId() || (npw && npw != tlw))
-                markDirtyOnScreen(w->rect(), w, w->mapTo(tlw, QPoint()));
+            if (w != tlw) {
+                QWidget *npw = w->nativeParentWidget();
+                if (w->internalWinId() || (npw && npw != tlw)) {
+                    if (!w->internalWinId())
+                        w = npw;
+                    QWidgetPrivate *wPrivate = w->d_func();
+                    if (!wPrivate->needsFlush)
+                        wPrivate->needsFlush = new QRegion;
+                    appendDirtyOnScreenWidget(w);
+                }
+            }
         }
 
         // We might have newly exposed areas on the screen if this function was
@@ -1277,13 +1286,8 @@ void QWidgetBackingStore::doSync()
             }
         }
     }
-    for (int i = 0; i < dirtyRenderToTextureWidgets.count(); ++i) {
-        QWidget *w = dirtyRenderToTextureWidgets.at(i);
-        resetWidget(w);
-        QWidget *npw = w->nativeParentWidget();
-        if (w->internalWinId() || (npw && npw != tlw))
-            markDirtyOnScreen(w->rect(), w, w->mapTo(tlw, QPoint()));
-    }
+    for (int i = 0; i < dirtyRenderToTextureWidgets.count(); ++i)
+        resetWidget(dirtyRenderToTextureWidgets.at(i));
     dirtyRenderToTextureWidgets.clear();
 #endif