QSGNode updatePaintNode() implementationo has memory leak?

mxyn

I have created a linux application using QML. I am drawing zones on a video. the zones change colors, and appear or disappear depending on system side information. This data for zone color and position is provided by a variable: m_zoneList

When I run my application for an extended period, I see the Mem used % start to grow. The more often I draw the zones, the faster the Mem used % grows. Could someone please take a look at this and see if I made a dumb mistake?

QSGNode *Zones::updatePaintNode(QSGNode * oldNode, UpdatePaintNodeData *)
{
#if 1
 QSGNode *root = static_cast<QSGNode *>(oldNode);
 if(!root) {
     root = new QSGNode;
 }

 root->removeAllChildNodes();
 int sz = m_zoneList.size();
 QColor fgnd;
 QColor bgnd;

 if(sz > 0)
 {
     int i = 0;
     while(i < sz)	// paint the contrast zone (bgnd color) then the normla zone (fgnd color)
     {
        //i = 0;
        QVariantList zList = m_zoneList.at(i).toList();
        fgnd.setNamedColor(zList.at(4).toString());
        bgnd.setNamedColor(zList.at(5).toString());
	QPointF xy1 = zList.at(0).toPointF();
	QPointF xy2 = zList.at(1).toPointF();
	QPointF xy3 = zList.at(2).toPointF();
	QPointF xy4 = zList.at(3).toPointF();
        //QPointF points[4] = {xy1, xy2, xy3, xy4};

        QSGFlatColorMaterial *cm = new QSGFlatColorMaterial;
        cm->setColor(bgnd);

        QSGGeometry *geoCZone = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 4);
        geoCZone->setLineWidth(6);
        geoCZone->setDrawingMode(QSGGeometry::DrawLineLoop);
        geoCZone->vertexDataAsPoint2D()[0].set(xy1.x(),xy1.y());
        geoCZone->vertexDataAsPoint2D()[1].set(xy2.x(),xy2.y());
        geoCZone->vertexDataAsPoint2D()[2].set(xy3.x(),xy3.y());
        geoCZone->vertexDataAsPoint2D()[3].set(xy4.x(),xy4.y());

        QSGGeometryNode *contrastZone = new QSGGeometryNode;
        contrastZone->setGeometry(geoCZone);
        contrastZone->setMaterial(cm);
        contrastZone->setFlag(QSGNode::OwnsGeometry);
        contrastZone->setFlag(QSGNode::OwnsMaterial);
         	
        QSGGeometry *geoZn = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 4);
        geoZn->setLineWidth(3);
        geoZn->setDrawingMode(QSGGeometry::DrawLineLoop);
        geoZn->vertexDataAsPoint2D()[0].set(xy1.x(),xy1.y());
        geoZn->vertexDataAsPoint2D()[1].set(xy2.x(),xy2.y());
        geoZn->vertexDataAsPoint2D()[2].set(xy3.x(),xy3.y());
        geoZn->vertexDataAsPoint2D()[3].set(xy4.x(),xy4.y());
	
        QSGFlatColorMaterial *z = new QSGFlatColorMaterial;
        z->setColor(fgnd);

        QSGGeometryNode *zone = new QSGGeometryNode; 	
        zone->setGeometry(geoZn);   
        zone->setMaterial(z);	
	zone->setFlag(QSGNode::OwnsGeometry);
        zone->setFlag(QSGNode::OwnsMaterial);

        root->appendChildNode(contrastZone);
        root->appendChildNode(zone);
	i++;
     }
 } 
return root;
#endif
}

sierdzio

@mxyn said in QSGNode updatePaintNode() implementationo has memory leak?:

@sierdzio Good point. But because I use setFlag(QSGNode::OwnsGeometry) and setFlag(QSGNODE::OwnsMaterial), this should not be an issue. By setting these flags, the objects should be deleted when the child node is deleted.

Yes, deleted. Not removed. So if you do:

delete root;

It will delete all child nodes.

Anyway, I'm only guessing this based on the fact that documentation does not mention what happens to a node when it's owned and removed. Perhaps I'm wrong. Check with address sanitizer to be sure.

sierdzio

removeAllChildNodes() does not delete the objects. So you keep creating new nodes with every run of updatePaintNode().

mxyn

@sierdzio Good point. But because I use setFlag(QSGNode::OwnsGeometry) and setFlag(QSGNODE::OwnsMaterial), this should not be an issue. By setting these flags, the objects should be deleted when the child node is deleted. At least, I think that's what the documentation is saying.

https://doc.qt.io/qt-5/qsgnode.html#Flag-enum

https://stackoverflow.com/questions/46394155/how-to-use-qsggeometrynode-without-causing-a-memory-leak-and-ensure-correct-clea

sierdzio

@mxyn said in QSGNode updatePaintNode() implementationo has memory leak?:

@sierdzio Good point. But because I use setFlag(QSGNode::OwnsGeometry) and setFlag(QSGNODE::OwnsMaterial), this should not be an issue. By setting these flags, the objects should be deleted when the child node is deleted.

Yes, deleted. Not removed. So if you do:

delete root;

It will delete all child nodes.

Anyway, I'm only guessing this based on the fact that documentation does not mention what happens to a node when it's owned and removed. Perhaps I'm wrong. Check with address sanitizer to be sure.

mxyn

@sierdzio Thank you! I tried your suggestion and it solved my problem. I wish the documentation was more explicit about needing to delete the nodes!

sierdzio

@mxyn said in QSGNode updatePaintNode() implementationo has memory leak?:

I wish the documentation was more explicit about needing to delete the nodes!

If you have time, please open a suggestion on Qt bugtracker and submit a patch for the documentation.