QPainter won't draw
-
I've got a class "ComponentArea" which is derived from QScrollArea. The ComponentArea has some other QWidget-derivatives in it.
I modify the palette and enable mouseTracking in the constructor:ComponentArea::ComponentArea(QWidget* parent) : QScrollArea(parent) { QPalette palette = this->palette(); palette.setColor(QPalette::Base, Qt::white); palette.setColor(QPalette::Window, Qt::white); palette.setColor(QPalette::AlternateBase, Qt::white); this->setPalette(palette); this->setMouseTracking(true); }
The mouseMoveEvent calls repaint(), which triggers the paintEvent:
void ComponentArea::mouseMoveEvent(QMouseEvent *event) { if(pressedSocket_first != 0) { mousePos_global = event->globalPos(); this->repaint(); } } void ComponentArea::paintEvent(QPaintEvent *event) { Q_UNUSED(event) QPainter* painter = new QPainter(this); painter->eraseRect(QRect(QPoint(0,0), QPoint(this->size().width(), this->size().height()))); painter->setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::SquareCap)); if(pressedSocket_first != 0) { QPoint socketPos = this->mapFromGlobal(pressedSocket_first->mapToGlobal(QPoint(0,0))); socketPos.setX(socketPos.x() + pressedSocket_first->size().width() /2); socketPos.setY(socketPos.y() + pressedSocket_first->size().height() /2); QPoint mousePos = this->mapFromGlobal(mousePos_global); painter->drawLine(socketPos, mousePos); } }
The line does not appear. With debugging, I made sure that drawLine() is in fact reached and the values of socketPos and mousePos make sense. Nevertheless the line does not appear. What am I doing wrong? Thanks in advance!
-
Hi and welcome to devnet,
QPainter
paints only whenendPaint()
is called (the destructor calls endPaint as well).
I suggest to change your code using a stack variable instead a pointerQPainter painter
instead ofQPainte *painter
also because you never delete created painter -
@mcosta Hm, neither calling painter->end() manually nor using a "usual" variable solves it. I draw in the ComponentView's children the same way, and it works perfectly.