Avoid flicker when invalidate is propagated in a widget/layout hierarchy

* Do not call invalidate from activateRecursive().
  This resulted in that a layout was invalidated as many times as there
  were items in the layout.

* Several improvements. Do not call resize(size()) too often.
  Calling resize() from the widgetEvent() is not very nice though...

* Remove commented out code

* make sure layout is activated even if the widget does not change size

* activate the layout if the resize is same as size()

* In order to not break existing apps, make this an opt-in feature
  with QGraphicsLayout::setInstantInvalidatePropagation(true);

Reviewed-by: Frederik Gladhorn
Reviewed-by: John Tapsell

1 files changed, 71 insertions, 34 deletions

diff --git a/src/gui/graphicsview/qgraphicswidget.cpp b/src/gui/graphicsview/qgraphicswidget.cpp
index 675a5c5..141e305 100644
--- a/src/gui/graphicsview/qgraphicswidget.cpp
+++ b/src/gui/graphicsview/qgraphicswidget.cpp
@@ -354,8 +354,10 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
         newGeom = rect;
         newGeom.setSize(rect.size().expandedTo(effectiveSizeHint(Qt::MinimumSize))
                                    .boundedTo(effectiveSizeHint(Qt::MaximumSize)));
-        if (newGeom == d->geom)
-            return;
+
+        if (newGeom == d->geom) {
+            goto relayoutChildrenAndReturn;
+        }
 
         // setPos triggers ItemPositionChange, which can adjust position
         wd->inSetGeometry = 1;
@@ -363,8 +365,9 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
         wd->inSetGeometry = 0;
         newGeom.moveTopLeft(pos());
 
-        if (newGeom == d->geom)
-           return;
+        if (newGeom == d->geom) {
+            goto relayoutChildrenAndReturn;
+        }
 
          // Update and prepare to change the geometry (remove from index) if the size has changed.
         if (wd->scene) {
@@ -375,35 +378,54 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
     }
 
     // Update the layout item geometry
-    bool moved = oldPos != pos();
-    if (moved) {
-        // Send move event.
-        QGraphicsSceneMoveEvent event;
-        event.setOldPos(oldPos);
-        event.setNewPos(pos());
-        QApplication::sendEvent(this, &event);
-        if (wd->inSetPos) {
-            //set the new pos
-            d->geom.moveTopLeft(pos());
-            emit geometryChanged();
-            return;
+    {
+        bool moved = oldPos != pos();
+        if (moved) {
+            // Send move event.
+            QGraphicsSceneMoveEvent event;
+            event.setOldPos(oldPos);
+            event.setNewPos(pos());
+            QApplication::sendEvent(this, &event);
+            if (wd->inSetPos) {
+                //set the new pos
+                d->geom.moveTopLeft(pos());
+                emit geometryChanged();
+                goto relayoutChildrenAndReturn;
+            }
+        }
+        QSizeF oldSize = size();
+        QGraphicsLayoutItem::setGeometry(newGeom);
+        // Send resize event
+        bool resized = newGeom.size() != oldSize;
+        if (resized) {
+            QGraphicsSceneResizeEvent re;
+            re.setOldSize(oldSize);
+            re.setNewSize(newGeom.size());
+            if (oldSize.width() != newGeom.size().width())
+                emit widthChanged();
+            if (oldSize.height() != newGeom.size().height())
+                emit heightChanged();
+            QGraphicsLayout *lay = wd->layout;
+            if (QGraphicsLayout::instantInvalidatePropagation()) {
+                if (!lay || lay->isActivated()) {
+                    QApplication::sendEvent(this, &re);
+                }
+            } else {
+                QApplication::sendEvent(this, &re);
+            }
         }
     }
-    QSizeF oldSize = size();
-    QGraphicsLayoutItem::setGeometry(newGeom);
-    // Send resize event
-    bool resized = newGeom.size() != oldSize;
-    if (resized) {
-        QGraphicsSceneResizeEvent re;
-        re.setOldSize(oldSize);
-        re.setNewSize(newGeom.size());
-        if (oldSize.width() != newGeom.size().width())
-            emit widthChanged();
-        if (oldSize.height() != newGeom.size().height())
-            emit heightChanged();
-        QApplication::sendEvent(this, &re);
-    }
+
     emit geometryChanged();
+relayoutChildrenAndReturn:
+    if (QGraphicsLayout::instantInvalidatePropagation()) {
+        if (QGraphicsLayout *lay = wd->layout) {
+            if (!lay->isActivated()) {
+                QEvent layoutRequest(QEvent::LayoutRequest);
+                QApplication::sendEvent(this, &layoutRequest);
+            }
+        }
+    }
 }
 
 /*!
@@ -1052,16 +1074,31 @@ void QGraphicsWidget::updateGeometry()
     QGraphicsLayoutItem *parentItem = parentLayoutItem();
 
     if (parentItem && parentItem->isLayout()) {
-        parentItem->updateGeometry();
+        if (QGraphicsLayout::instantInvalidatePropagation()) {
+            static_cast<QGraphicsLayout *>(parentItem)->invalidate();
+        } else {
+            parentItem->updateGeometry();
+        }
     } else {
         if (parentItem) {
+            // This is for custom layouting
             QGraphicsWidget *parentWid = parentWidget();    //###
             if (parentWid->isVisible())
                 QApplication::postEvent(parentWid, new QEvent(QEvent::LayoutRequest));
+        } else {
+            /**
+             * If this is the topmost widget, post a LayoutRequest event to the widget.
+             * When the event is received, it will start flowing all the way down to the leaf
+             * widgets in one go. This will make a relayout flicker-free.
+             */
+            if (QGraphicsLayout::instantInvalidatePropagation())
+                QApplication::postEvent(static_cast<QGraphicsWidget *>(this), new QEvent(QEvent::LayoutRequest));
+        }
+        if (!QGraphicsLayout::instantInvalidatePropagation()) {
+            bool wasResized = testAttribute(Qt::WA_Resized);
+            resize(size()); // this will restrict the size
+            setAttribute(Qt::WA_Resized, wasResized);
         }
-        bool wasResized = testAttribute(Qt::WA_Resized);
-        resize(size()); // this will restrict the size
-        setAttribute(Qt::WA_Resized, wasResized);
     }
 }