@jsulm Thanks! @JonB I see, thanks for the clarification!

Hey, not sure if you found the solution yet. But you can try this: QGraphicsPixmapItem *pixmapItem = new QGraphicsPixmapItem; pixmapItem->setPixmap(QPixmap(":/images/pixmap.png")); _scene->addItem(pixmapItem); pixmapItem->setRotation(pixmapItem->rotation() + 45.0); QGraphicsRectItem *boundingRect = new QGraphicsRectItem(pixmapItem->sceneBoundingRect()); QPen outlinePen; outlinePen.setWidth(2); outlinePen.setColor(Qt::red); boundingRect->setPen(outlinePen); _scene->addItem(boundingRect); I believe what you want is the sceneBoundingRect() and not the boundingRect().

@Christian-Ehrlicher said in Collisions with custom QGraphicsItem that inherits from QObject: @JonB But it will behave exactly as his class wrt to the pointers: Absolutely true! Hence I said Apart from the answer @Christian-Ehrlicher has given to the question you ask. This is just a suggestion for if OP does want equivalent for the class CustomRect : public QObject, public QGraphicsItem. Not that it will change any behaviour wrt to pointers question.

@JonB You’re right, Thanks, QGraphicsItemGroup did the trick. I just needed to set the transform origin point to the centre of the red rectangle. Now the desired effect is achieved by this code: #include "game.h" #include <QGraphicsItemGroup> QGraphicsItemGroup* g = new QGraphicsItemGroup; Game::Game() { player = new QGraphicsRectItem(); rectItem = new QGraphicsRectItem(); m_view = new QGraphicsView(this); m_view->setSceneRect(QRectF(0,0,800,600)); this->setBackgroundBrush(Qt::black); m_view->setScene(this); m_view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff); m_view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff); m_view->setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform); m_view->setViewportUpdateMode(QGraphicsView::NoViewportUpdate); m_view->show(); player->setRect(0,0,100,100); player->setBrush(Qt::red); player->setPos(400,300); player->setFocus(); rectItem->setRect(0,0,100,100); rectItem->setBrush(Qt::green); rectItem->setPos(400,330); this->addItem(g); player->setZValue(10); rectItem->setZValue(1); g->addToGroup(player); g->addToGroup(rectItem); g->setTransformOriginPoint(player->pos().x() + player->boundingRect().width()/2 ,player->pos().y() + player->boundingRect().height()/2); } void Game::advance() { } void Game::keyPressEvent(QKeyEvent *event) { switch(event->key()) { case Qt::Key_Left : g->moveBy(-5,0); break; case Qt::Key_Right : g->moveBy(5,0); break; case Qt::Key_Up : g->moveBy(0,-5); break; case Qt::Key_Down : g->moveBy(0,5); break; case Qt::Key_Q : g->setRotation(g->rotation()- 3); break; case Qt::Key_W : g->setRotation(g->rotation() +3); break; } update(); }

I guess I provided inadequate subtext for that example. It's documentation in a project I work on, explaining that qObject.signal.connect(lambda: anotherQObject.function(arg)) is unsafe in PyQt if anotherQObject might be destroyed before qObject. The same would happen in C++ with QObject::connect(qObject, &MyClass::signal, [&]() { anotherQObject->function(arg); }); In C++, one possible solution is to use QObject::Connect(sender, signal, context object, functor). To the best of my knowledge In PyQt5, and I suspect in PySide2/Qt for Python, there is no equivalent. You can write one by taking the connection object returned by object.signal.connect() and using it in a slot connected to anotherQObject.destroyed.

@MegAmaNeo1 In @jsulm's outline code you need a signal named pressed in CustomItem for connect(&item, CustomItem::pressed ..., and you also need an array/QVector of bool named pressed for pressed[i]. You'll presumably need to rename one of them. And where he writes void QGraphicsItem::mousePressEvent he means your void CustomItem::mousePressEvent override.

@SGaist yes, hovering will be okay too. I just didn't think that constant mouse tracking is such a problem.

boundingRect does not depend on the position of the item with respect to the scene since it is in coordinates with respect to the item. I recommend you review https://doc.qt.io/qt-5/graphicsview.html so that you understand the different coordinate systems that are handled.

@incam https://doc.qt.io/qt-5/qpropertyanimation.html

@mrjj Thanks, so I hit the limit. I'll try not to go over that.

Since QGraphicsItem::pos() Returns the position of the item in parent coordinates. So the item and its parent item are not in the same coordinate system. I think you should calculate the offset between pos() and value, then calculate the new pos of mParentItem by adding offset to mParentItem->pos().

@SGaist I have tried many things so there are a few comments Here the minimal code below: main.cpp: #include "QApplication" #include "graphicsitemgroup.h" #include "qgraphicslinearlayout.h" #include "qgraphicsscene.h" #include "qgraphicsview.h" #include "graphicswidget.h" int main(int argc, char *argv[]) { QApplication app(argc, argv); auto widget = new QGraphicsWidget(nullptr, Qt::Window); auto item_0 = new GraphicsItemGroup(widget); auto item_1 = new GraphicsItemGroup(widget); auto linearLayout = new QGraphicsLinearLayout(); linearLayout->addItem(item_0); linearLayout->addItem(item_1); widget->setLayout(linearLayout); QGraphicsScene scene; scene.addItem(widget); QGraphicsView view(&scene); view.setResizeAnchor(QGraphicsView::AnchorViewCenter); view.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff); view.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff); view.show(); return app.exec(); } graphicsitemgroup.h: #ifndef GRAPHICSITEMGROUP_H #define GRAPHICSITEMGROUP_H #include "qgraphicslayoutitem.h" #include "QGraphicsItemGroup" #include "qsize.h" class GraphicsItem; /** * @brief Placeholder for graphics items */ class GraphicsItemGroup : public QGraphicsLayoutItem, public QGraphicsItemGroup { public: GraphicsItemGroup(QGraphicsItem* parent = nullptr); virtual ~GraphicsItemGroup(); void setGeometry(const QRectF& geometry) override; QSizeF sizeHint(Qt::SizeHint which, const QSizeF& constraint = QSizeF()) const override; // QRectF boundingRect() const override; void paint(QPainter *painter, const QStyleOptionGraphicsItem* option, QWidget* widget) override; private: QSizeF m_size; GraphicsItem* m_item; }; #endif // GRAPHICSITEMGROUP_H graphicsitemgroup.cpp: #include "graphicsitemgroup.h" #include "graphicsitem.h" #include "qpainter.h" #include "qdebug.h" GraphicsItemGroup::GraphicsItemGroup(QGraphicsItem* parent) : QGraphicsItemGroup(parent) , m_size(QSize(100, 100)) , m_item(new GraphicsItem(QSizeF(50, 50))) { addToGroup(m_item); setGraphicsItem(this); } GraphicsItemGroup::~GraphicsItemGroup() = default; void GraphicsItemGroup::setGeometry(const QRectF& geometry) { prepareGeometryChange(); QGraphicsLayoutItem::setGeometry(geometry); setPos(geometry.topLeft()); qDebug() << __PRETTY_FUNCTION__; } QSizeF GraphicsItemGroup::sizeHint(Qt::SizeHint which, const QSizeF& constraint) const { switch (which) { case Qt::MinimumSize: case Qt::PreferredSize: return m_size; case Qt::MaximumSize: default: break; } return constraint; } //QRectF GraphicsItemGroup::boundingRect() const //{ // return QRectF(QPointF(0, 0), geometry().size()); //} void GraphicsItemGroup::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) { painter->drawRect(QRectF(QPointF(0, 0), geometry().size())); } graphicsitem.h: #ifndef GRAPHICSITEM_H #define GRAPHICSITEM_H #include "qgraphicslayoutitem.h" #include "qgraphicsitem.h" #include "qsize.h" class QRectF; class QPainter; class QStyleOptionGraphicsItem; class GraphicsItem : /*public QGraphicsLayoutItem,*/ public QGraphicsItem { public: GraphicsItem(QSizeF size, QGraphicsItem* parent = nullptr); virtual ~GraphicsItem(); // void setGeometry(const QRectF& geometry) override; // QSizeF sizeHint(Qt::SizeHint which, const QSizeF& constraint = QSizeF()) const override; QRectF boundingRect() const override; void paint(QPainter *painter, const QStyleOptionGraphicsItem* option, QWidget* widget) override; private: QSizeF m_size; }; #endif graphicsitem.cpp: #include "graphicsitem.h" #include "qpainter.h" #include "qrect.h" #include "qdebug.h" GraphicsItem::GraphicsItem(QSizeF size, QGraphicsItem* parent) : QGraphicsItem(parent) , m_size(size) { // setGraphicsItem(this); } GraphicsItem::~GraphicsItem() = default; //void GraphicsItem::setGeometry(const QRectF& geometry) //{ // prepareGeometryChange(); // QGraphicsLayoutItem::setGeometry(geometry); // setPos(geometry.topLeft()); // // qDebug() << __PRETTY_FUNCTION__; //} // //QSizeF GraphicsItem::sizeHint(Qt::SizeHint which, const QSizeF& constraint) const //{ // switch (which) // { // case Qt::MinimumSize: // case Qt::PreferredSize: // return m_size; // case Qt::MaximumSize: // default: // break; // } // // return constraint; //} QRectF GraphicsItem::boundingRect() const { return QRectF(QPointF(20, 20), m_size); } void GraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem* option, QWidget* widget) { painter->drawRect(boundingRect()); } CMakeLists.txt: cmake_minimum_required(VERSION 3.0) project(GraphicsLayoutExample) find_package(Qt5 COMPONENTS Core REQUIRED Widgets REQUIRED Gui REQUIRED ) add_executable(${CMAKE_PROJECT_NAME} main.cpp graphicsitemgroup.cpp graphicsitem.cpp ) target_include_directories(${CMAKE_PROJECT_NAME} PUBLIC .) target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE Qt5::Widgets Qt5::Core Qt5::Gui) I would like to have the graphics item (here a little rectangle) to be resized depending on the a graphics item group (the latter paints another rectangle just to have a visual on what is going on). In the future, I have planned to put two graphics items (one over the other) in the group. Thanks for your help.

@amansahil Check after setting the position if polygon->scenePos() - clickPoint == (0, 0). If it is, there's a problem with the event->scenePos(), and if not, there's a problem with how the polygon position is being set. The right conversion would be polygon->setPos( clickPoint - polygonParent->scenePos() ) mapFromScene() is better than mapToScene() since you have the coordinates in the scene frame and you want them in local coordinates. But it still isn't quite right! You specify position in the local parent coordinates, not the local item frame. So that approach to use is polygon->setPos( polygonParent->mapFromScene(clickPoint) )

@mrjj Yes, it worked. Thank you!

For sure it can be measured, and I do agree with the approach "if it works fine, just use it". But I am still curious, why clipping is expensive in the first place, so that the warning exists in the docs? Has anyone experienced performance impact while actively using clipping for real-time chart?

It appears that QGraphicsScene checks if position of item is visible in view and then draws/dont draws it... returning qgraphicsScene->sceneRect() as boundingRect on my curve "solved" the issues but its a problem for selectable items... hmmm

Hi I think you just broke GraphicsView normal handling. Try also calling base class mousePressEvent as it might use for the actual item selection void GraphicsView::mousePressEvent(QMouseEvent *event) { if(event->buttons().testFlag(Qt::LeftButton)) { int x,y; x = event->pos().x(); y = event->pos().y(); qDebug() << x << ", " << y; QPointF point = mapToScene(x, y); QGraphicsEllipseItem *ellipse; ellipse = scene->addEllipse(point.x(),point.y(),5,5,QPen(Qt::red), QBrush(Qt::red)); ellipse->setFlag(QGraphicsEllipseItem::ItemIsMovable); } // call base class QGraphicsView::mousePressEvent(event); }

Hi, Can you provide a minimal compilable code that shows that behaviour ?

@SGaist Possibly yes... I'm back to this & lost again... I think I figured out the last problem without needing it, but now I need it again... Scenario = bezier curve, 4 points, first start, control left, control right, endpoints. Start and end can never cross each other on Z-axis. Control left can not pass end on the Z-axis and control Right can not pass start on z-axis either. Control points are children of start/endpoints. (Hope this make sense...) So what I need to find out is... location of End point while being inside Control Left event. I need to somehow map scenePos() of End point to my Control Left local space.... here is some debuging I was trying to do... (test case, moving right control point towards left Start item) targetPos : QPointF(348,-478) // scenePos() of Start item myPos : QPointF(336,-617) // scenePos() of rightControl scenePos() - already invalid position because we passed the Z location of targetPos item. myLocPos : QPointF(-237,2) This should match other item loc at some point... localPos of rightControl mapFromScene: QPointF(12,139) // mappings mapToItem : QPointF(113,-477) // mappings mapFromItem : QPointF(583,-479) // mappings one of mappings should return a number close to myLocPos but none of them do :- ( Debug code : qDebug() << "oh snap!" << "\n targetPos : " << itemPos << "\n myPos : " << myPos << "\n myLocPos : " << newPos << "local pos of rightControl item" << "\n mapFromScene: " << mapFromScene(itemPos) << "\n mapToItem : " << mapToItem(items[x], itemPos) << "\n mapFromItem : " << mapFromItem(items[x], itemPos); Esentially this : Top left item, is the myPos/newPos variable newPos being local and myPos being scenePos(), item below is the "Start"

Hi, Without more details form you side, it looks like that's the function you are looking for.

Call fitInView on the GraphicsView with the Image whenever the size of the GraphicsView changes. The rest should work automatically.

Hi, I got the expected output from grab(QRect) https://stackoverflow.com/questions/16362191/qt-grab-widget-and-save-image m_graphicsView->grab(rect).save("OUT.jpg"); Thanks all.

@Lanparty said in Application crashes while accessing Pointers and while Hovering over custom QGraphicsItems: btw: how do I change the status of my post to "solved"? First post, Topic Tools button to the side.

Thanks @SGaist and @raven-worx , I try both methods to see which one to use better in my program.

Hi, What about QGraphicsProxyWidget ?

I found the problem. I was drawing the beats before the lines, so the lines took precedent over the beats since they are siblings. The solution was to either draw the beats last or set the Z value on the beat, not the note.

Hi As long as you dont do multiple inheritance , i think you base class design should work just fine. However, make sure to overrride int QGraphicsItem::type() const pr concrete class to make sure qgraphicsitem_cast() works.

@mrjj There are other obstacles that I need to overcome. But this way seems to be the solution that i am implementing. Thanks

@raven-worx I tried the following but didn't work out.. QGraphicsPixmapItem* item = new QGraphicsPixmapItem(QPixmap::fromImage(qImage, Qt::AutoColor)); m_ViewerScene->addItem(item); QGraphicsRectItem* rect = new QGraphicsRectItem(m_BoundingBox); m_ViewerScene->addItem(rect); rect->setParentItem(item); m_ViewerScene->update(); //add the resized QGraphicsPixmapItem to the pixmap item->setPixmap( item->pixmap().scaled(QSize(128, 32),Qt::IgnoreAspectRatio, Qt::SmoothTransformation)); qInfo()<<"Rect resize props:::"<<item->childItems()[0]->boundingRect(); m_BoundingBox = item->childItems()[0]->boundingRect(); later I'm drawing box, on the image in an other viewer, with m_BoundingBox. The grey area within the blue rectangle will be resized to 128 * 32, and then the red rectangle would be added on the resized image. How to get the co-ordinates of red rect on the resized image?

@Asperamanca Thanks for the reply, I fixed it by seperating the problem instead of making one compound Qgraphicsitem, which was the goal.

@kenchan I knew that. I want not stacking by z-order, I want simultaneous stacking. It works something like that by default (if opacity of items is 0.5 ) output = Merge(Merge(background, 0.5 × item1), 0.5 × item2) I want something like that output = Merge(background, 0.5 × item1, 0.5 × item2) aka simultaneous merge items to scene, so it not depends from z-order. (example — I want ⅓ background, ⅓ item1 and ⅓ item2, Indifferently to items z-order)