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  • How to display a QGraphicsScene?

    - by Chris
    I've got the following code and I'm not sure how to add the QGraphicsScene to my layout.. class MainForm(QDialog): def __init__(self, parent=None): super(MainForm, self).__init__(parent) self.scene = QGraphicsScene(self) self.scene.setSceneRect(0, 0, 500, 500) self.view = QGraphicsView() self.view.setRenderHint(QPainter.Antialiasing) self.view.setScene(self.scene) self.view.setFocusPolicy(Qt.NoFocus) zoomSlider = QSlider(Qt.Horizontal) zoomSlider.setRange(5, 200) zoomSlider.setValue(100) self.pauseButton = QPushButton("Pause") quitButton = QPushButton("Quit") layout = QVBoxLayout() layout.addWidget(zoomSlider) self.setLayout(layout) self.startTimer(10) How can I get my QGraphicsScene running? I'm new to Qt. Am I even supposed to be adding a QGraphicsScene to a layout/

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  • QGLWidget + QGraphicsScene + QGraphicsView problem

    - by matekm
    Hi! I would like to create a simple thumbnail viewer using QGLWidget, QGraphicsScene and QGraphicsView. And I have a problem with placing QGLWidget on QGraphicsScene. The code is similar to this: QGraphicsScene *testScene = new QGraphicsScene (0, 0, 400, 400, 0); QGLWidget *testWidget1 = new QGLWidget(); testWidget1->renderText("Test text1"); QGLWidget *testWidget2 = new QGLWidget(); testWidget2->renderText("Test text2"); testScene->addWidget(testWidget1); testScene->addWidget(testWidget2); QGraphicsView *testView = new QGraphicsView(); testView->setScene(testScene); testView->show() It is possible to place few QGLWidgets on QGraphicsScene/QGraphicsView? Where I doing something wrong? Is there any other component on which I could embed QGLWidgets and show them on the screen? Thanks for help

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  • Serializing QGraphicsScene contents

    - by Rob
    I am using the Qt QGraphicsScene class, adding pre-defined items such as QGraphicsRectItem, QGraphicsLineItem, etc. and I want to serialize the scene contents to disk. However, the base QGraphicsItem class (that the other items I use derive from) doesn't support serialization so I need to roll my own code. The problem is that all access to these objects is via a base QGraphicsItem pointer, so the serialization code I have is horrible: QGraphicsScene* scene = new QGraphicsScene; scene->addRect(QRectF(0, 0, 100, 100)); scene->addLine(QLineF(0, 0, 100, 100)); ... QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { if (item->type() == QGraphicsRectItem::Type) { QGraphicsRectItem* rect = qgraphicsitem_cast<QGraphicsRectItem*>(item); // Access QGraphicsRectItem members here } else if (item->type() == QGraphicsLineItem::Type) { QGraphicsLineItem* line = qgraphicsitem_cast<QGraphicsLineItem*>(item); // Access QGraphicsLineItem members here } ... } This is not good code IMHO. So, instead I could create an ABC class like this: class Item { public: virtual void serialize(QDataStream& strm, int version) = 0; }; class Rect : public QGraphicsRectItem, public Item { public: void serialize(QDataStream& strm, int version) { // Serialize this object } ... }; I can then add Rect objects using QGraphicsScene::addItem(new Rect(,,,)); But this doesn't really help me as the following will crash: QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { Item* myitem = reinterpret_class<Item*>(item); myitem->serialize(...) // FAIL } Any way I can make this work?

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  • Using custom coordinates with QGraphicsScene

    - by Rob
    I am experimenting with a WYSIWYG editor that allows a user to draw shapes on a page and the Qt graphics scene support seems perfect for this. However, instead of working in pixels I want all my QGraphicsItem objects to work in tenths of a millimetre but I don't know how to achieve this. For example: // Create a scene that is the size if an A4 page (2100 = 21cm, 2970 = 29.7cm) QGraphicsScene* scene = new QGraphicsScene(0, 0, 2100, 2970); // Add a rectangle located 1cm across, 1cm down, 5cm wide and 2cm high QGraphicsItem* item = scene->addRect(100, 100, 500, 200); ... QGraphicsView* view = new QGraphicsView(scene); setCentralWidget(view); Now, when I display the scene above I want the shapes to appear at correct size for the screen DPI. Is this simply a case of using QGraphicsView::scale or do I have to do something more complicated? Note that if I was using a custom QWidget instead then I would use QPainter::setWindow and QPainter::setViewport to create a custom mapping mode but I can't see how to do this using the graphics scene support.

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  • General advice about scaling on QGraphicsView/QGraphicsScene

    - by onurozcelik
    Hi, In my project I am using QGraphicsView/QGraphicsScene stuff. On my scene there will be regions that contains 2D graphics. Region count will be limited(Lets say 20) Users can choose to display one or more regions. If user choose to display one region I am going to show one region on scene If user choose to display n regions I am going to show n regions on scene I need a scaling logic to fit n regions on same scene. How can I achieve this?

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  • Artifacts when trying to draw background grid without anti-aliasing in a QGraphicsScene

    - by estan
    Hi folks, I'm trying to draw a background grid in the drawBackground() function of my QGraphicsScene subclass: void Scene::drawBackground(QPainter *painter, const QRectF &rect) { const int gridSize = 50; const int realLeft = static_cast<int>(std::floor(rect.left())); const int realRight = static_cast<int>(std::ceil(rect.right())); const int realTop = static_cast<int>(std::floor(rect.top())); const int realBottom = static_cast<int>(std::ceil(rect.bottom())); // Draw grid. const int firstLeftGridLine = realLeft - (realLeft % gridSize); const int firstTopGridLine = realTop - (realTop % gridSize); QVarLengthArray<QLine, 100> lines; for (qreal x = firstLeftGridLine; x <= realRight; x += gridSize) lines.append(QLine(x, realTop, x, realBottom)); for (qreal y = firstTopGridLine; y <= realBottom; y += gridSize) lines.append(QLine(realLeft, y, realRight, y)); //painter->setRenderHint(QPainter::Antialiasing); painter->setPen(QPen(QColor(220, 220, 220), 0.0)); painter->drawLines(lines.data(), lines.size()); // Draw axes. painter->setPen(QPen(Qt::lightGray, 0.0)); painter->drawLine(0, realTop, 0, realBottom); painter->drawLine(realLeft, 0, realRight, 0); } However, unless I turn on anti-aliasing, moving items around will sometimes leave artifacts in the grid (areas where it's not drawn). It seems it mostly happens at low zoom levels, when the view is zoomed out a bit. Any ideas what I might be doing wrong here? I'd really don't want to turn anti-aliasing on since the lines are strictly horizontal and vertical, and I'd like them to be as crisp as possible. Any help is much appriciated, Regards, Elvis

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  • Qt/C++, Problems with large QImage

    - by David Günzel
    I'm pretty new to C++/Qt and I'm trying to create an application with Visual Studio C++ and Qt (4.8.3). The application displays images using a QGraphicsView, I need to change the images at pixel level. The basic code is (simplified): QImage* img = new QImage(img_width,img_height,QImage::Format_RGB32); while(do_some_stuff) { img->setPixel(x,y,color); } QGraphicsPixmapItem* pm = new QGraphicsPixmapItem(QPixmap::fromImage(*img)); QGraphicsScene* sc = new QGraphicsScene; sc->setSceneRect(0,0,img->width(),img->height()); sc->addItem(pm); ui.graphicsView->setScene(sc); This works well for images up to around 12000x6000 pixel. The weird thing happens beyond this size. When I set img_width=16000 and img_height=8000, for example, the line img = new QImage(...) returns a null image. The image data should be around 512,000,000 bytes, so it shouldn't be too large, even on a 32 bit system. Also, my machine (Win 7 64bit, 8 GB RAM) should be capable of holding the data. I've also tried this version: uchar* imgbuf = (uchar*) malloc(img_width*img_height*4); QImage* img = new QImage(imgbuf,img_width,img_height,QImage::Format_RGB32); At first, this works. The img pointer is valid and calling img-width() for example returns the correct image width (instead of 0, in case the image pointer is null). But as soon as I call img-setPixel(), the pointer becomes null and img-width() returns 0. So what am I doing wrong? Or is there a better way of modifying large images on pixel level? Regards, David

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  • Qt Qbrush issue

    - by Solitaire
    What is the difference in the following code, QGraphicsScene * scence = new QGraphicsScene(); QBrush *brush = new QBrush((QColor(60,20,20))); scence->setBackgroundBrush(*brush); QGraphicsView *view = new QGraphicsView(); view->setScene(scence); //view->setBackgroundBrush(*brush); //view->setCacheMode(QGraphicsView::CacheBackground); view->showFullScreen(); gives black color background QGraphicsScene * scence = new QGraphicsScene(); QBrush *brush = new QBrush(); brush->setColor(QColor(60,20,20)); scence->setBackgroundBrush(*brush); QGraphicsView *view = new QGraphicsView(); view->setScene(scence); //view->setBackgroundBrush(*brush); //view->setCacheMode(QGraphicsView::CacheBackground); view->showFullScreen(); it gives nothing.

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  • QT: trouble with qobject_cast

    - by weevilo
    I have derived QGraphicsItem and QGraphicsScene classes. I want the items to be able to call scene() and get a derviedGraphicsItem * instead of a QGraphicsItem *, so I reimplemented QGraphicsScene::itemAt to return a derived pointer. DerivedItem* DerivedScene::itemAt( const QPointF &position, const QTransform &dt ) const { return qobject_cast< DerivedItem * >( QGraphicsScene::itemAt(position, dt) ); } I get the following error (Qt 4.6, GCC 4.4.3 on Ubuntut 10.4) scene.cpp: In member function ‘DerivedItem* DerivedScene::itemAt(qreal, qreal, const QTransform&) const’: scene.cpp:28: error: no matching function for call to ‘qobject_cast(QGraphicsItem*)’ I then noticed QGraphicsItem doesn't inherit QObject, so I made my derived QGraphicsItem class have multiple inheritance from QObject and QGraphicsItem, and after adding the Q_OBJECT macro and rebuilding the project I get the same error. Am I going about this the wrong way? I know it's supposed to be bad design to try to cast a parent class as a child, but in this case it seems like what I want, since my derived item class has new functionality and its objects need a way to call that new functionality on items around themselves, and asking the items scene object with itemAt() seems like the best way - but I need itemAt() to return a pointer of the right type. I can get around this by having the derived items cast the QGraphicsItem * returned by QGraphicsScene::itemAt() using dynamic_cast, but I don't really understand why that works and not qobject_cast, or the benefits or disadvantages to using dynamic_cast vs. qobject_cast.

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  • How can let Qt Graphics View Framework support custom layers

    - by jnblue
    Qt's graphics view frameworks is very powerful, but I have not found a way to support custom layers. In Qt, there is a QGraphicsScene::ItemLayer,but QGraphicsScene renders all items are in this layer. I want manage the items with several layers, Just like Illustrator and CorelDraw. all the item only in the current layer will receive the event, be selected or get the key focus etc.. Other layers(not current layer) will not receive all scene event. The most reasons of using layers is I could catalogue a large number of items more clearly.And without needing transfer events to all the layers' items ,I think the graphics frameworks will be more efficient. The last question, does QGraphicsView support rendering server stacked graphics scenes at the same time? If support, I think the "custom layers" can be solved in this way. Thanks very much!

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  • Overlapping labels in Qt fridge magnets example

    - by bullettime
    I want to modify the fridge magnets example provided with Qt in a way that when I drag a label and drop it over another, it will push the label beneath the dragged label to the side, so they will never overlap one another. I've seen how collision is detected in the colliding mice example, where it uses a QGraphicsScene to draw the QGraphicsItem mice on, and scene()-collidingItems(this) to see which mice are colliding. The problem is that the fridge magnets example uses a class that inherits QWidget in place of QGraphicsScene, so there's no collidingItems() method to check when we have a collision. How do I go about doing that?

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  • QGraphicsView scrolling and image scaling/cropping

    - by boohoo
    I would like to have a background image in my QGraphicsView that is always scaled (and cropped if necessary) to the size of the viewport, without scrollbars and without scrolling with the keyboard and mouse. The example below is what I am doing to scale and crop an image in the viewport, but I am using random values for the cropping that are pulled out of the aether. I would like a logical solution? MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui->setupUi(this); scene = new QGraphicsScene(this); ui->graphicsView->resize(800, 427); // MainWindow is 800x480, GraphicsView is 800x427. I want an image that // is the size of the graphicsView. ui->graphicsView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff); ui->graphicsView->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff); // the graphicsView still scrolls if the image is too large, but // displays no scrollbars. I would like it not to scroll (I want to // add a scrolling widget into the QGraphicsScene later, on top of // the background image.) QPixmap *backgroundPixmap = new QPixmap(":/Valentino_Bar_Prague.jpg"); QPixmap sized = backgroundPixmap->scaled( QSize(ui->graphicsView->width(), ui->graphicsView->height()), Qt::KeepAspectRatioByExpanding); // This scales the image too tall QImage sizedImage = QImage(sized.toImage()); QImage sizedCroppedImage = QImage(sizedImage.copy(0,0, (ui->graphicsView->width() - 1.5), (ui->graphicsView->height() + 19))); // so I try to crop using copy(), and I have to use these values // and I am unsure why. QGraphicsPixmapItem *sizedBackground = scene->addPixmap( QPixmap::fromImage(sizedCroppedImage)); sizedBackground->setZValue(1); ui->graphicsView->setScene(this->scene); } I would like to know a way to scale and crop an image to the size of the QGraphicsView that will work even when I resize the QGraphicsView. Where are the 1.5 and 19 coming from?

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  • How to update a QPixmap in a QGraphicsView with PyQt

    - by pops
    I am trying to paint on a QPixmap inside a QGraphicsView. The painting works fine, but the QGraphicsView doesn't update it. Here is some working code: #!/usr/bin/env python from PyQt4 import QtCore from PyQt4 import QtGui class Canvas(QtGui.QPixmap): """ Canvas for drawing""" def __init__(self, parent=None): QtGui.QPixmap.__init__(self, 64, 64) self.parent = parent self.imH = 64 self.imW = 64 self.fill(QtGui.QColor(0, 255, 255)) self.color = QtGui.QColor(0, 0, 0) def paintEvent(self, point=False): if point: p = QtGui.QPainter(self) p.setPen(QtGui.QPen(self.color, 1, QtCore.Qt.SolidLine)) p.drawPoints(point) def clic(self, mouseX, mouseY): self.paintEvent(QtCore.QPoint(mouseX, mouseY)) class GraphWidget(QtGui.QGraphicsView): """ Display, zoom, pan...""" def __init__(self): QtGui.QGraphicsView.__init__(self) self.im = Canvas(self) self.imH = self.im.height() self.imW = self.im.width() self.zoomN = 1 self.scene = QtGui.QGraphicsScene(self) self.scene.setItemIndexMethod(QtGui.QGraphicsScene.NoIndex) self.scene.setSceneRect(0, 0, self.imW, self.imH) self.scene.addPixmap(self.im) self.setScene(self.scene) self.setTransformationAnchor(QtGui.QGraphicsView.AnchorUnderMouse) self.setResizeAnchor(QtGui.QGraphicsView.AnchorViewCenter) self.setMinimumSize(400, 400) self.setWindowTitle("pix") def mousePressEvent(self, event): if event.buttons() == QtCore.Qt.LeftButton: pos = self.mapToScene(event.pos()) self.im.clic(pos.x(), pos.y()) #~ self.scene.update(0,0,64,64) #~ self.updateScene([QtCore.QRectF(0,0,64,64)]) self.scene.addPixmap(self.im) print('items') print(self.scene.items()) else: return QtGui.QGraphicsView.mousePressEvent(self, event) def wheelEvent(self, event): if event.delta() > 0: self.scaleView(2) elif event.delta() < 0: self.scaleView(0.5) def scaleView(self, factor): n = self.zoomN * factor if n < 1 or n > 16: return self.zoomN = n self.scale(factor, factor) if __name__ == '__main__': import sys app = QtGui.QApplication(sys.argv) widget = GraphWidget() widget.show() sys.exit(app.exec_()) The mousePressEvent does some painting on the QPixmap. But the only solution I have found to update the display is to make a new instance (which is not a good solution). How do I just update it?

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  • How do I controll clipping with non-opaque graphics-item's in Qt?

    - by JJacobsson
    I have a bunch of QGraphicsSvgItem's in a QGraphicsScene that are drawn connected by QGraphicsLineItem's. This show's a graph of a tree-structure. What I want to do is provide a feature where everything but a selected sub-tree becomes transparent. A kind of "highlight this sub-tree" feature. That part was easy, but the results are ugly because now the lines can be seen through the semi-transparent svg's. I am looking for some way to still clip other QGraphicsItem's in the scene to the svg item's, giving the effect that the svg's are semi-transparent windows to the background. I know this code does not use svg's but I figure you can replace that yourself if you are so inclined. int main(int argc, char *argv[]) { QApplication app(argc, argv); QGraphicsScene scene; for( int i = 0; i < 10; ++i ) { QGraphicsLineItem* line = new QGraphicsLineItem; line->setLine( i * 25.0 + 1.0, 0, i * 25.0 + 23.0, 0 ); scene.addItem( line ); } for( int i = 0; i < 11; ++i ) { QGraphicsEllipseItem* ellipse = new QGraphicsEllipseItem; ellipse->setRect( (i * 25.0) - 9.0, -9.0, 18.0, 18.0f ); ellipse->setBrush( QBrush( Qt::green, Qt::SolidPattern ) ); ellipse->setOpacity( 0.5 ); scene.addItem( ellipse ); } QGraphicsView view( &scene ); view.show(); return app.exec(); } I would like the line's to not be seen behind the circle's. I have tried fiddling with the depth-buffer and the stencil buffer using opengl rendering to no avail. How do I get the QGraphicsSvgItem's (or QGraphicsEllipseItem's in the example code) to still clip the lines even though they are semi-transparent?

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  • Qt - drag and drop with graphics view framework

    - by David Davidson
    I'm trying to make a simple draggable item using the graphics framework. Here's the code for what I did so far: Widget class: class Widget : public QWidget { Q_OBJECT public: Widget(QWidget *parent = 0); ~Widget(); }; Widget::Widget(QWidget *parent) : QWidget(parent) { DragScene *scene = new DragScene(); DragView *view = new DragView(); QHBoxLayout *layout = new QHBoxLayout(); DragItem *item = new DragItem(); view->setAcceptDrops(true); scene->addItem(item); view->setScene(scene); layout->addWidget(view); this->setLayout(layout); } Widget::~Widget() { } DragView class: class DragView : public QGraphicsView { public: DragView(QWidget *parent = 0); }; DragView::DragView(QWidget *parent) : QGraphicsView(parent) { setRenderHints(QPainter::Antialiasing); } DragScene class: class DragScene : public QGraphicsScene { public: DragScene(QObject* parent = 0); protected: void dragEnterEvent(QGraphicsSceneDragDropEvent *event); void dragMoveEvent(QGraphicsSceneDragDropEvent *event); void dragLeaveEvent(QGraphicsSceneDragDropEvent *event); void dropEvent(QGraphicsSceneDragDropEvent *event); }; DragScene::DragScene(QObject* parent) : QGraphicsScene(parent) { } void DragScene::dragEnterEvent(QGraphicsSceneDragDropEvent *event){ } void DragScene::dragMoveEvent(QGraphicsSceneDragDropEvent *event){ } void DragScene::dragLeaveEvent(QGraphicsSceneDragDropEvent *event){ } void DragScene::dropEvent(QGraphicsSceneDragDropEvent *event){ qDebug() << event->pos(); event->acceptProposedAction(); DragItem *item = new DragItem(); this->addItem(item); item->setPos(event->pos()); } DragItem class: class DragItem : public QGraphicsItem { public: DragItem(QGraphicsItem *parent = 0); QRectF boundingRect() const; void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0); protected: void mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event); void mouseMoveEvent(QGraphicsSceneMouseEvent *event); void mousePressEvent(QGraphicsSceneMouseEvent *event); void mouseReleaseEvent(QGraphicsSceneMouseEvent *event); }; DragItem::DragItem(QGraphicsItem *parent) : QGraphicsItem(parent) { setFlag(QGraphicsItem::ItemIsMovable); } QRectF DragItem::boundingRect() const{ const QPointF *p0 = new QPointF(-10,-10); const QPointF *p1 = new QPointF(10,10); return QRectF(*p0,*p1); } void DragItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){ if(painter == 0) painter = new QPainter(); painter->drawEllipse(QPoint(0,0),10,10); } void DragItem::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event){ } void DragItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event){ } void DragItem::mousePressEvent(QGraphicsSceneMouseEvent *event){ QMimeData* mime = new QMimeData(); QDrag* drag = new QDrag(event->widget()); drag->setMimeData(mime); drag->exec(); } void DragItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event){ } main.cpp instantiates a Widget and shows it. When I try to drag the circle, the app just creates another circle over the original one, regardless of where I release the drag. qDebug() in DragScene's dropEvent() shows QPointF(0,0) everytime the drag ends. I'm having a hard time trying to understand exactly what I have to do, which classes I should subclass, which methods needs to be overriden, to make this work. The documentation on this isn't very detailed. I'd like to know how to make this work, and if there's some other, more comprehensive resource to learn about the graphics view framework, besides the official documentation (which is excellent btw, but it would be great if there was a more detailed treatise on the subject). EDIT: Following badgerr's advice, I replaced item-pos() in DragScene::dropEvent() with item-scenePos(), now the drop event creates a new circle in the drop site, which is more or less what I wanted. But the original circle is still in place, and while the drag is in progress, the item doesn't follow the mouse cursor. The QGraphicsSceneDragDropEvent documentation says that pos() should return the cursor position in relation to the view that sent the event, which, unless I got it wrong, shouldn't be (0,0) all the time. Weird. I've read in a forum post that you can use QDrag::setPixMap() to show something during the drag, and in examples I've seen pictures being set as pixmaps, but how do I make the pixmap just like the graphics item I'm supposed to be dragging?

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  • QWidget keyPressEvent override

    - by eaigner
    Hi there, I'm trying for half an eternity now overriding QWidgets keyPressEvent function in QT but it just won't work. I've to say i am new to CPP, but I know ObjC and standard C. My problem looks like this: class QSGameBoard : public QWidget { Q_OBJECT public: QSGameBoard(QWidget *p, int w, int h, QGraphicsScene *s); signals: void keyCaught(QKeyEvent *e); protected: virtual void keyPressEvent(QKeyEvent *event); }; QSGameBoard is my QWidget subclass and i need to override the keyPressEvent and fire a SIGNAL on each event to notify some registered objects. My overridden keyPressEvent in QSGameBoard.cpp looks like this: void QSGameBoard::keyPressEvent(QKeyEvent *event) { printf("\nkey event in board: %i", event->key()); //emit keyCaught(event); } When i change QSGameBoard:: to QWidget:: it receives the events, but i cant emit the signal because the compiler complains about the scope. And if i write it like this the function doesn't get called at all. What's the problem here?

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  • How to use custom drawing in QGraphicsViews in PyQt?

    - by DSblizzard
    I need to view QGraphicsScene in 2 QGraphicsViews with condition that they have different scale factors for items in scene. Closest function which I found is drawItems(), but as far I can understand, it must be called manually. How to repaint views automatically? I have these two code fragments in program: class TGraphicsView(QGraphicsView): def __init__(self, parent = None): print("__init__") QGraphicsView.__init__(self, parent) def drawItems(self, Painter, ItemCount, Items, StyleOptions): print("drawItems") Brush = QBrush(Qt.red, Qt.SolidPattern) Painter.setBrush(Brush) Painter.drawEllipse(0, 0, 100, 100) ... Mw.gvNavigation = TGraphicsView(Mw) # Mw - main window Mw.gvNavigation.setGeometry(0, 0, Size1, Size1) Mw.gvNavigation.setScene(Mw.Scene) Mw.gvNavigation.setSceneRect(0, 0, Size2, Size2) Mw.gvNavigation.show() _init_ works, Mw.gvNavigation is displayed and there are Mw.Scene items in it, but drawItems() isn't called.

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  • Subclassing QGraphicsItemGroup

    - by onurozcelik
    Hi everyone I have system that has classes derived from QGraphicsWidget. I manage derived class objects in layouts on QGraphicsScene. Now I need a compound item that contain two or more QGraphicsWidget in it and also I need to put that item inside my layout. So I choose QGraphicsItemGroup and write I class like this. class CompositeItem : public QGraphicsItemGroup,public QGraphicsLayoutItem { ... }; I only implemented sizeHint function again. When add CompositeItem instance to layout it does not shown. What may cause this? Where I made wrong?

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  • How set opacity on QGraphicsItem

    - by La Chamelle
    Hello, i have a inherited from QGraphicsScene and QGraphicsItem to create my own classes. I use Qt 4.6. I want to set a specific opacity on each items of my scene. I use setOpacity : setOpacity method, but its not the result i hope. I want to have for example one item opaque and an other transparent (to see the desktop, or the other application). But if i dont set the opacity of the QGraphicsView to 0.5, i have not the transparancy. And if the QGraphicsView is set to 0.5, the item is not real opaque. What should i do ? Thanks you.

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  • C++ class initialisation containing class variable initialization

    - by Phil Hannent
    I noticed some code of a colleague today that initialized class variables in the initialization. However it was causing a warning, he says because of the order they are in. My question is why is it better to do variable initialization where it currently is and not within the curly brackets? DiagramScene::DiagramScene( int slideNo, QRectF screenRect, MainWindow* parent ) : QGraphicsScene( screenRect, parent ), myParent( parent ), slideUndoImageCurrentIndex(-1), nextGroupID(0), m_undoInProgress(false), m_deleteItemOnNextUndo(0) line(0), path(0) { /* Setup default brush for background */ scDetail->bgBrush.setStyle(Qt::SolidPattern); scDetail->bgBrush.setColor(Qt::white); setBackgroundBrush(scDetail->bgBrush); }

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  • Lots of pointer casts in QGraphicsView framework and performance

    - by kleimola
    Since most of the convenience functions of QGraphicsScene and QGraphicsItem (such as items(), collidingItems(), childItems() etc.) return a QList you're forced to do lots of qgraphicsitem_cast or static_cast and QGraphicsItem::Type() checks to get hold of the actual items when you have lots of different type of items in the scene. I thought doing lots of subclass casts were not a desirable coding style, but I guess in this case there are no other viable way, or is there? QList<QGraphicsItem *> itemsHit = someItem->collidingItems(Qt::IntersectsItemShape); foreach (QGraphicsItem *item, itemsHit) { if (item->type() == QGraphicsEllipseItem::type()) { QGraphicsEllipseItem *ellipse = qgraphicsitem_cast<QGraphicsEllipseItem *>(item); // do something } else if (item->type() == MyItemSubclass::type()) { MyItemSubClass *myItem = qgraphicsitem_cast<MyItemSubClass *>(item); // do something } // etc } The above qgraphicsitem_cast could be replaced by static_cast since correct type is already verified. When doing lots of these all the time (very dynamic scene), will the numerous casting affect performance beyond the normal if-else evaluation?

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  • Overloading the QDataStream << and >> operators for a user-defined type

    - by Alex Wood
    I have a an object I'd like to be able to read and write to/from a QDataStream. The header is as follows: class Compound { public: Compound(QString, QPixmap*, Ui::MainWindow*); void saveCurrentInfo(); void restoreSavedInfo(QGraphicsScene*); void setImage(QPixmap*); QString getName(); private: QString name, homeNotes, addNotes, expText; Ui::MainWindow *gui; QPixmap *image; struct NMRdata { QString hnmrText, cnmrText, hn_nmrText, hn_nmrNucl, notes; int hnmrFreqIndex, cnmrFreqIndex, hn_nmrFreqIndex, hnmrSolvIndex, cnmrSolvIndex, hn_nmrSolvIndex; }*nmr_data; struct IRdata { QString uvConc, lowResMethod, irText, uvText, lowResText, highResText, highResCalc, highResFnd, highResFrmla, notes; int irSolvIndex, uvSolvIndex; }*ir_data; struct PhysicalData { QString mpEdit, bpEdit, mpParensEdit, bpParensEdit, rfEdit, phyText, optAlpha, optConc, elemText, elemFrmla, notes; int phySolvIndex, optSolvIndex; }*physical_data; }; For all intensive purposes, the class just serves as an abstraction for a handful of QStrings and a QPixmap. Ideally, I would be able to write a QList to a QDataStream but I'm not exactly sure how to go about doing this. If operator overloading is a suitable solution, would writing code like friend QDataStream& operator << (QDataStream&,Compound) { ... } be a potential solution? I'm very open to suggestions! Please let me know if any further clarification is needed.

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  • What is the most efficient way to display decoded video frames in Qt?

    - by Jason
    What is the fastest way to display images to a Qt widget? I have decoded the video using libavformat and libavcodec, so I already have raw RGB or YCbCr 4:2:0 frames. I am currently using a QGraphicsView with a QGraphicsScene object containing a QGraphicsPixmapItem. I am currently getting the frame data into a QPixmap by using the QImage constructor from a memory buffer and converting it to QPixmap using QPixmap::fromImage(). I like the results of this and it seems relatively fast, but I can't help but think that there must be a more efficient way. I've also heard that the QImage to QPixmap conversion is expensive. I have implemented a solution that uses an SDL overlay on a widget, but I'd like to stay with just Qt since I am able to easily capture clicks and other user interaction with the video display using the QGraphicsView. I am doing any required video scaling or colorspace conversions with libswscale so I would just like to know if anyone has a more efficient way to display the image data after all processing has been performed. Thanks.

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