I am trying to draw a 10 pixel radius circle on a QGraphicsScene that is anchored on the center and doesn't transform (change size) when the scene is zoomed.
I have tried using the QGraphicsEllipseItem with the QGraphicsItem::ItemIgnoresTransformations flag, but it still transforms when the scene is zoomed.
Is this possible with standard graphics items, or do I need to create my own and do the paint event manually?
The following code does what I think you're looking for. It creates a single 10 pixel immutable circle that anchors itself to the centre of the scene as well as 10 larger, movable, circles that obey the scaling transform applied...
#include <iostream>
#include <QApplication>
#include <QGraphicsEllipseItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QPainter>
int main (int argc, char **argv)
{
QApplication app(argc, argv);
QGraphicsView view;
QGraphicsScene scene;
view.setScene(&scene);
QGraphicsEllipseItem immutable(0, 0, 20, 20);
immutable.setFlag(QGraphicsItem::ItemIgnoresTransformations);
immutable.setPen(Qt::NoPen);
immutable.setBrush(Qt::blue);
scene.addItem(&immutable);
QObject::connect(&scene, &QGraphicsScene::sceneRectChanged,
[&](const QRectF &rect)
{
immutable.setPos(rect.center() - 0.5 * immutable.boundingRect().center());
});
for (int i = 0; i < 10; ++i) {
auto *e = new QGraphicsEllipseItem(20, 20, 50, 50);
e->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);
scene.addItem(e);
}
view.show();
view.setTransform(QTransform::fromScale(5, 2));
return app.exec();
}
I started using Qt5 a little while ago and I don't know how to set the position of my drawing in my window.
I have a Drawing class which is a QWidget and which contains my paintEvent() function and other functions; and a MainWindow class which contains some widgets. So in order to display my Qpainter, I have to include it in my layout, which is the main window layout, but the window doesn't adapt to the Qpainter at all; the dimensions of the buttons, sliders .. adapt so as to organize themselves and occupy all the space of my window, but they totally ignore my Qpainter and it partly disappears if I put at least 2 widgets.
Do you have any solutions to better manage the position of these elements?
main.cpp :
#include <QtGui>
#include <QApplication>
#include "mywidget.h"
int main( int argc, char **argv )
{
QApplication app(argc, argv);
MainWindow window;
window.show();
return app.exec();
}
mywidget.h :
#ifndef MYWIDGET_H
#define MYWIDGET_H
#include <QtGui>
#include <QWidget>
#include <QSlider>
#include <QScrollBar>
#include <QApplication>
#include <QGridLayout>
#include <QObject>
#include <QPoint>
#include <QLabel>
#include <QPolygon>
class Drawing : public QWidget
{
Q_OBJECT
public:
Drawing();
void paintEvent(QPaintEvent* e);
public slots:
void slide(int abscisse);
void rotate();
private:
QPoint o;
QPoint a;
QPoint b;
QPoint c;
QPoint d;
};
//--------------------------------------
class MainWindow : public QWidget
{
Q_OBJECT
public:
MainWindow();
private:
QSlider* m_slider1;
QSlider* m_slider2;
QGridLayout* m_layout;
Drawing* m_dessin;
};
#endif // MYWIDGET_H
mywidget.cpp :
#include "mywidget.h"
#include <iostream> //POUR LES TESTS
MainWindow::MainWindow() : QWidget()
{
setGeometry(330, 140, 840, 620);
m_slider1 = new QSlider(Qt::Horizontal, this);
m_slider1->setRange(150, 650);
m_slider1->setSliderPosition(400);
m_slider2 = new QSlider(Qt::Horizontal, this);
m_slider2->setSliderPosition(50);
m_layout = new QGridLayout;
m_layout->addWidget(new QLabel("Translation Horizontale"), 1, 0);
m_layout->addWidget(m_slider1, 2, 0);
m_layout->addWidget(new QLabel("Rotation"), 0, 1);
m_layout->addWidget(m_slider2, 1, 1);
m_dessin = new Drawing;
m_layout->addWidget(m_dessin, 0, 0);
setLayout(m_layout);
QObject::connect(m_slider1, SIGNAL(valueChanged(int)), m_dessin, SLOT(slide(int)));
QObject::connect(m_slider2, SIGNAL(valueChanged(int)), m_dessin, SLOT(rotate()));
}
//--------------------------------------------------------
Drawing::Drawing() : QWidget(), o(400, 150), a(o.x()-50 , o.y()-50), b(o.x()+50 , o.y()-50), c(o.x()+50 , o.y()+50), d(o.x()-50 , o.y()+50) {}
void Drawing::paintEvent(QPaintEvent *e) {
QPolygon poly;
poly << a << b << c << d;
QWidget::paintEvent(e); // effectue le comportement standard
QPainter painter(this); // construire
painter.setPen( QPen(Qt::white, 2) ); // personnaliser
painter.drawPolygon(poly); // dessiner
}
void Drawing::slide(int abscisse) {
if (a == QPoint(o.x()-50 , o.y()-50)) {
o.setX(abscisse);
a.setX(o.x()-50);
b.setX(o.x()+50);
c.setX(o.x()+50);
d.setX(o.x()-50);
}
else {
o.setX(abscisse);
a.setX(o.x());
b.setX(o.x()+75);
c.setX(o.x());
d.setX(o.x()-75);
}
update();
}
void Drawing::rotate() {
if (a == QPoint(o.x()-50 , o.y()-50)) {
a = QPoint(o.x() , o.y()+75);
b = QPoint(o.x()+75 , o.y());
c = QPoint(o.x() , o.y()-75);
d = QPoint(o.x()-75 , o.y());
}
else {
a = QPoint(o.x()-50 , o.y()-50);
b = QPoint(o.x()+50 , o.y()-50);
c = QPoint(o.x()+50 , o.y()+50);
d = QPoint(o.x()-50 , o.y()+50);
}
update();
}
Snapshots:
After having seen the snapshots of OP, I thought about what might been happen.
The layout of OP doesn't look that wrong.
I still believe that the layout plays only a minor role in OPs issue.
I tried to reproduce OPs issue with an even smaller MCVE of mine.
My testQGridLayout:
#include <QtWidgets>
class Drawing: public QFrame {
public:
Drawing(QWidget *pQParent = nullptr);
virtual ~Drawing() = default;
Drawing(const Drawing&) = delete;
Drawing& operator=(const Drawing&) = delete;
protected:
virtual void paintEvent(QPaintEvent *pQEvent) override;
};
Drawing::Drawing(QWidget* pQParent):
QFrame(pQParent)
{
setFrameStyle(Box | Plain);
}
void Drawing::paintEvent(QPaintEvent* pQEvent)
{
{ QPainter qPainter(this);
qPainter.drawText(QPoint(40, 40),
QString("Size: %1 x %2").arg(width()).arg(height()));
qPainter.setPen(Qt::red);
qPainter.drawRect(300, 100, 200, 200);
}
// call base class paint event to keep it working
QFrame::paintEvent(pQEvent);
}
class MainWindow: public QWidget {
public:
MainWindow(QWidget *pQParent = nullptr);
virtual ~MainWindow() = default;
MainWindow(const MainWindow&) = delete;
MainWindow& operator=(const MainWindow&) = delete;
private:
QGridLayout _qGrid;
Drawing _qDrawing;
QSlider _qSliderT;
QSlider _qSliderR;
};
MainWindow::MainWindow(QWidget *pQParent):
QWidget(pQParent),
_qSliderT(Qt::Horizontal),
_qSliderR(Qt::Horizontal)
{
resize(840, 620);
_qGrid.addWidget(&_qDrawing, 0, 0);
_qGrid.addWidget(new QLabel("Translation Horizontal"), 1, 0);
_qSliderT.setRange(150, 650);
_qSliderT.setSliderPosition(400);
_qGrid.addWidget(&_qSliderT, 2, 0);
_qGrid.addWidget(new QLabel("Rotation"), 1, 1);
_qSliderR.setSliderPosition(50);
_qGrid.addWidget(&_qSliderR, 2, 1);
setLayout(&_qGrid);
}
int main(int argc, char **argv)
{
qDebug() << "Qt Version:" << QT_VERSION_STR;
QApplication app(argc, argv);
// setup GUI
MainWindow qWinMain;
qWinMain.setWindowTitle("Test QGridLayout");
qWinMain.show();
// runtime loop
return app.exec();
}
Output:
Qt Version: 5.15.1
I made some changes to exclude what is a possible issue and what not.
I derived my Drawing from QFrame. Thus, it was easy to give it a visible border. As expected, my Drawing _qDrawing occupies only the space above the first slider (QSlider _qSliderT; in my case).
I added output of widget size to the Drawing::paintEvent() to see its size. Then I added the painting of a red rectangle. For that, I cared to cover a space which is partly inside the widget and partly below and right of it.
This is what I conclude:
As exposed in the OPs code, the layout should be the same.
OPs rectangle is always drawn at the same coordinates. Hence, it doesn't get visible until the Drawing grows large enough (with the main window).
The origin of the QPainter (i.e. QPoint(0, 0)) is the upper left corner of the widget. This can be changed by applying transformations but I couldn't see this in OPs code. (The effect of the sliders, I neglect for now.)
Though, there are still some things which are not clear to me:
The Drawing should clip the painting. Hence, I wonder, how OPs rectangle can appear over the rotate slider. Either, the OP used a span for the Drawing m_dessin, or the widget doesn't clip painting on the paint engine the OP uses. (The look is quite different than mine. Thus, it might be a different platform.)
The layout which can be seen in OPs snapshots doesn't match the exposed code. In OPs snapshot, the Drawing occupies all extra space resulting from growing the main window. This is only possible when QGridLayout::setRowStretch()/GridLayout::setColumnStretch() had been used (as recommended in my first comment). However, the exposed code doesn't contain them.
To check this out, I changed the layout in MainWindow::MainWindow():
MainWindow::MainWindow(QWidget *pQParent):
QWidget(pQParent),
_qSliderT(Qt::Horizontal),
_qSliderR(Qt::Horizontal)
{
resize(840, 620);
_qGrid.setRowStretch(0, 1);
_qGrid.setColumnStretch(0, 1);
_qGrid.addWidget(&_qDrawing, 0, 0, 1, 2);
_qGrid.addWidget(new QLabel("Translation Horizontal"), 1, 0);
_qSliderT.setRange(150, 650);
_qSliderT.setSliderPosition(400);
_qGrid.addWidget(&_qSliderT, 2, 0);
_qGrid.addWidget(new QLabel("Rotation"), 1, 1);
_qSliderR.setSliderPosition(50);
_qGrid.addWidget(&_qSliderR, 2, 1);
setLayout(&_qGrid);
}
Output:
Now, the layout seems to match the one of OPs snapshots.
Trying resize:
This looks exactly as it should:
the Drawing _qDrawing shrinks and grows with the main window size
the painting is clipped if the size of Drawing _qDrawing becomes too small to cover it.
Final Conclusion:
There is nothing wrong in OPs layout.
IMHO, OP is not yet fully clear about how coordinate systems apply in QPainter.
For this, I can warmly recommend an extra page of the Qt online doc., precisely dedicated to this topic:
Qt Doc.: Coordinate System
Continuation:
How to add a vertical slider:
class MainWindow: public QWidget {
public:
MainWindow(QWidget *pQParent = nullptr);
virtual ~MainWindow() = default;
MainWindow(const MainWindow&) = delete;
MainWindow& operator=(const MainWindow&) = delete;
private:
QGridLayout _qGrid;
Drawing _qDrawing;
QSlider _qSliderV;
QSlider _qSliderT;
QSlider _qSliderR;
};
MainWindow::MainWindow(QWidget *pQParent):
QWidget(pQParent),
_qSliderV(Qt::Vertical),
_qSliderT(Qt::Horizontal),
_qSliderR(Qt::Horizontal)
{
resize(840, 620);
_qGrid.setRowStretch(0, 1);
_qGrid.setColumnStretch(0, 1);
_qGrid.addWidget(&_qDrawing, 0, 0, 1, 2);
_qGrid.addWidget(&_qSliderV, 0, 2);
_qGrid.addWidget(new QLabel("Translation Horizontal"), 1, 0);
_qSliderT.setRange(150, 650);
_qSliderT.setSliderPosition(400);
_qGrid.addWidget(&_qSliderT, 2, 0);
_qGrid.addWidget(new QLabel("Rotation"), 1, 1, 1, 2);
_qSliderR.setSliderPosition(50);
_qGrid.addWidget(&_qSliderR, 2, 1, 1, 2);
setLayout(&_qGrid);
}
Output:
To achieve this specific layout, I placed the _qSliderV into column 2 and gave _qSliderR (and its label) a column span of 2 as well.
To illustrate this, I added a sketch of the resulting grid to the above snapshot:
Which behavior would you like for your Drawing widget?
By default it will be resized freely by the layout, you can change this by using QWidget::sizeHint() and QWidget::sizePolicy(). You'll find detailed information in Qt documentation about custom widgets and layouts.
I want to fit (child) widget into the parent widget size. So if the parent window is too small to display all the elements of the child widget the QScrollArea should appear otherwise it should be invisible.
I have attached the pictures for a better understanding.
The black box is where I want my scroll to appear. Since when we reduce the size of the window, sometimes you can't see the scroll bar (as displayed in the below picture) it doesn't look elegant enough for big projects.
Please help me with the same, thanks in advance.
Here's the sample code that I used for example:
int main(int argc, char *argv[]){
QApplication a(argc, argv);
QScrollPractice w;
QDialog * dlg = new QDialog();
//dlg->setGeometry(100, 100, 260, 260);
dlg->setMinimumSize(150, 200);
QScrollArea *scrollArea = new QScrollArea(dlg);
scrollArea->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
scrollArea->setWidgetResizable(true);
//scrollArea->setGeometry(10, 10, 200, 200);
//scrollArea->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Ignored);
//QSizePolicy sizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
scrollArea->setSizePolicy(sizePolicy);
QWidget *widget = new QWidget(scrollArea);
scrollArea->setWidget(widget);
QVBoxLayout *layout = new QVBoxLayout(widget);
widget->setLayout(layout);
for (int i = 0; i < 10; i++)
{
QPushButton *button = new QPushButton(QString("%1").arg(i));
layout->addWidget(button);
}
dlg->show();
return a.exec();
}
Your Dialog is missing a layout as well. Thats the reason the scrollArea Widget isnt spread out across the dialog.
#include <QApplication>
#include <QDialog>
#include <QScrollArea>
#include <QVBoxLayout>
#include <QPushButton>
int main(int argc, char* argv[]){
QApplication a(argc, argv);
QDialog* dlg = new QDialog();
dlg->setMinimumSize(150, 200);
QScrollArea* scrollArea = new QScrollArea(dlg);
scrollArea->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
scrollArea->setWidgetResizable(true);
QWidget* widget = new QWidget(scrollArea);
scrollArea->setWidget(widget);
QVBoxLayout* dlgLayout = new QVBoxLayout();
dlg->setLayout( dlgLayout );
dlgLayout->addWidget( scrollArea );
QVBoxLayout* layout = new QVBoxLayout(widget);
widget->setLayout(layout);
for (int i = 0; i < 10; i++)
{
QPushButton* button = new QPushButton(QString("%1").arg(i));
layout->addWidget(button);
}
dlg->show();
return a.exec();
}
I modified your code to make it run and compileable, also I added antoher QVBoxLayout and added it to the dialog. Then the scrollArea gets added to that Layout. Hope this helps.
I need a pushbutton to either fill or not fill the entire space provided by a QGridLayout cell upon the creation of the button (the alignment value is loaded from file). I've simplified my situation with the following code. During run-time, users can set the alignment of the button - either making it fill the entire layout cell or nicely centered. It works so long as the button didn't start off with NULL alignment specified. Yet, I need the ability to start off with a NULL alignment (i.e. the button fills the space of the layout cell). When initially aligning with NULL, what is getting set to make the button lock into a AlignVCenter setting and how can I get the button to return to acting like it was initialized with something other than null alignment?
I'm using Qt 4.8 on Ubuntu 12.04 LTS
#include <QPushButton>
#include <QGridLayout>
#include <QMainWindow>
#include <QApplication>
class MyWidget : public QWidget {
Q_OBJECT
QPushButton* m_pb;
QGridLayout* m_gl;
protected slots:
void pbClicked();
public:
MyWidget(QWidget* parent = 0);
};
MyWidget::MyWidget(QWidget* parent): QWidget(parent)
{
m_pb = new QPushButton(tr("push me"));
connect(m_pb, SIGNAL(clicked()), this, SLOT(pbClicked()));
m_gl = new QGridLayout();
//use (1) to see button expand when button is pressed
//use (2) to show that I can't start off expanded
/*1*/ //m_gl->addWidget(m_pb, 0, 0, Qt::AlignCenter); // creates desired effect
/*2*/ //m_gl->addWidget(m_pb, 0, 0, 0); //does not create desired effect
setLayout(m_gl);
}
void MyWidget::pbClicked(){
//will expand button so long as initial alignment is not NULL
m_gl->setAlignment(m_pb, 0);
}
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
MyWidget* widget = new MyWidget();
QMainWindow window;
window.setCentralWidget(widget);
window.show();
return app.exec();
}
#include "main.moc"
The "desired" behavior that you see is in fact an error, and I will file a bug report for it. Thanks for spotting it - nice corner case.
You need to set the size policy of the button to expanding in both directions. Buttons normally don't want to expand vertically, so if you tried a variant that toggles the alignment, you'd see that it works only horizontally, and that's correct.
This is a simple demonstration that shows the correct behavior that also fulfills your needs.
#include <QPushButton>
#include <QGridLayout>
#include <QApplication>
class AlignButton : public QPushButton {
Q_OBJECT
Qt::Alignment m_alignment;
Q_SLOT void clicked() {
m_alignment ^= Qt::AlignCenter;
parentWidget()->layout()->setAlignment(this, m_alignment);
label();
}
void label() {
setText(QString("Alignment = %1").arg(m_alignment));
}
public:
AlignButton(Qt::Alignment alignment, QWidget * parent = 0) :
QPushButton(parent),
m_alignment(alignment)
{
connect(this, SIGNAL(clicked()), SLOT(clicked()));
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
label();
}
};
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QWidget window;
QGridLayout layout(&window);
layout.addWidget(new AlignButton(0), 0, 0, 0);
layout.addWidget(new AlignButton(Qt::AlignCenter), 1, 0, Qt::AlignCenter);
window.setMinimumSize(500, 200);
window.show();
return app.exec();
}
#include "main.moc"
In the code below, I have three QGraphicsItems that are laid out by QGraphicsLinearLayout, which is set as layout to a QGraphicsWidget.
#include <QApplication>
#include <QBrush>
#include <QDebug>
#include <QGraphicsItem>
#include <QGraphicsLayoutItem>
#include <QGraphicsLinearLayout>
#include <QGraphicsRectItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsWidget>
#include <QPen>
class MyShape : public QGraphicsRectItem, public QGraphicsLayoutItem {
public:
MyShape(void) {
setPen(QPen(QBrush(Qt::black), 1));
setBrush(QBrush(Qt::green));
setRect(0, 0, 20, 20);
}
virtual QSizeF sizeHint(Qt::SizeHint which,
const QSizeF& constraint = QSizeF()) const {
Q_UNUSED(which);
Q_UNUSED(constraint);
return boundingRect().size();
}
virtual void setGeometry(const QRectF& rect) {
setPos(rect.topLeft());
}
};
int main(int argc, char** argv) {
QApplication app(argc, argv);
QGraphicsScene scene;
MyShape* shape1 = new MyShape;
MyShape* shape2 = new MyShape;
MyShape* shape3 = new MyShape;
scene.addItem(shape1);
scene.addItem(shape2);
scene.addItem(shape3);
QGraphicsLinearLayout* layout = new QGraphicsLinearLayout;
layout->addItem(shape1);
layout->addItem(shape2);
layout->addItem(shape3);
QGraphicsWidget* container = new QGraphicsWidget;
container->setLayout(layout);
scene.addItem(container);
container->setPos(300, 300); // This doesn't appear to have any affect
// Item for indicating origin
QGraphicsRectItem* tmp = scene.addRect(0, 0, 2, 2, QPen(),
QBrush(Qt::green));
tmp->setPos(0, 0);
qDebug() << tmp->scenePos();
qDebug() << container->scenePos();
QGraphicsView view;
view.setScene(&scene);
view.centerOn(0, 0);
view.show();
return app.exec();
}
Then, I try to move the QGraphicsWidget within the scene by calling setPos(), but it doesn't appear to work (the QGraphicsItems remain in the same place). However, something appears to happen since the scrollbars change. It seems that the QGraphicsWidget moves, without taking the QGraphicsItems along with it.
Why?
EDIT:
By suggestion from DerManu, I changed the inheritance of MyShape to QGraphicsWidget, and with the following code, it works:
#include <QApplication>
#include <QBrush>
#include <QDebug>
#include <QGraphicsItem>
#include <QGraphicsLayoutItem>
#include <QGraphicsLinearLayout>
#include <QGraphicsRectItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsWidget>
#include <QPen>
class MyShape : public QGraphicsWidget {
public:
MyShape(void) {
setMinimumSize(20, 20);
setMaximumSize(20, 20);
setPreferredSize(20, 20);
}
QRectF boundingRect(void) const {
QRectF box(0, 0, 22, 22);
box.translate(box.center() * -1);
return box;
}
void paint(QPainter* painter,
const QStyleOptionGraphicsItem* option,
QWidget* widget) {
Q_UNUSED(option);
Q_UNUSED(widget);
// Set box border appearance
painter->setPen(QPen(Qt::black, 1));
// Set box background appearance
painter->setBrush(QBrush(Qt::green));
QRectF box(0, 0, 20, 20);
box.translate(box.center() * -1);
painter->drawRect(box);
}
};
int main(int argc, char** argv) {
QApplication app(argc, argv);
QGraphicsScene scene;
MyShape* shape1 = new MyShape;
MyShape* shape2 = new MyShape;
MyShape* shape3 = new MyShape;
scene.addItem(shape1);
scene.addItem(shape2);
scene.addItem(shape3);
QGraphicsLinearLayout* layout = new QGraphicsLinearLayout(Qt::Vertical);
layout->addItem(shape1);
layout->addItem(shape2);
layout->addItem(shape3);
QGraphicsWidget* container = new QGraphicsWidget;
container->setLayout(layout);
scene.addItem(container);
container->setPos(200, 200); // This doesn't appear to have any affect
scene.setSceneRect(-300, -300, 600, 600);
// Item for indicating origin
QGraphicsRectItem* tmp = scene.addRect(0, 0, 2, 2, QPen(),
QBrush(Qt::green));
tmp->setPos(0, 0);
qDebug() << tmp->scenePos();
qDebug() << container->scenePos();
QGraphicsView view;
view.setScene(&scene);
view.centerOn(0, 0);
view.show();
return app.exec();
}
So what is it that QGraphicsWidget provides that I missed in the original code such that using setPos on the container item correctly moves the position of the MyShape items?