i think of to write primitive snake. i have window where program paints random lines.
but i can't think up how to catch pressed key to change direction of painted line.
class QUpdatingPathIte : public QGraphicsPathItem
{
void advance(int phase)
{
if (phase == 0)
return;
int x,y;
int w,a,s,d;
char c;
//
// HOW TO MAKE THIS HERE? (i had done early in console application)
// but i can't do this in GUI , what should i do?
scanf("%c",&c);
if (c=='w')
{ x=-20; y=0; }
else if (c=='s')
{ x=20; y=0; }
else if (c=='a')
{ x=0; y=-20; }
else if(c=='d')
{ x=0; y=20; }
QPainterPath p = path();
p.lineTo(x, y);
setPath(p);
}
};
#include <QtGui/QApplication>
#include "dialog.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene s;
QGraphicsView v(&s);
QUpdatingPathIte item;
item.setPen(QPen(QColor("black")));
s.addItem(&item);
v.show();
QTimer *timer = new QTimer(&s);
timer->connect(timer, SIGNAL(timeout()), &s, SLOT(advance()));
timer->start(500);
return a.exec();
}
QGraphicsView inherits from from QWidget because it inherits from QAbstractScrollArea. You should create a custom subclass of QGraphicsView and just override the function keyPressEvent(). Example:
class SnakeView : public QGraphicsView
{
protected:
keyPressEvent(QKeyEvent *e)
{
// Do something
// Otherwise pass to the graphics view
QGraphicsView::keyPressEvent(e)
}
};
Then rather than creating a QGraphicsView object you would create a SnakeView object.
QGraphicsView reimplements keyPressEvent and will forward events to the QGraphicsScene. QGraphicsScene supports key presses through its keyPressEvent handler. By default the QGraphicsScene will forward that key press to the current QGraphicsItem through its keyPressEvent function.
Given the above, what you likely want to do is reimplement the keyPressEvent handler in your QUpdatingPathItem:
void QUpdatingPathItem::keyPressEvent(QKeyEvent *event)
{
switch (event->key()) {
case Key::Key_A: /* do something useful */; break;
case Key::Key_S: /* do something useful */; break;
case Key::Key_W: /* do something useful */; break;
case Key::Key_D: /* do something useful */; break;
}
}
I couldn't really follow what you were trying to do in your advance method, so I can't offer much in the way of a suggested handler.
Besides implementing QObject::installEventFilter, you could also subclass any of QGraphicsView, QGraphicsScene, or QGraphicsItem and override the keyPressEvent function.
thanks you all. Then I didn't reach my aim. But time went on and I've come to the same problem and now I solved it.
There are right and worth answers but then I wasn't good enough to put them together because no one was full and sufficient. Now I did it so:
HEADER FILE "header.h"
class MyGraphicView: public QGraphicsView
{
Updating *m_update;
public:
MyGraphicView(Updating *update);
void keyPressEvent(QKeyEvent *event);
};
#include "header.h"
void GraphicView::keyPressEvent(QKeyEvent *event)
{
switch ( event->key())
{case Qt::Key_Up:
m_update->move_up();
break;
case Qt::Key_Down:
m_update->move_down();
break;
case Qt::Key_Left:
{ m_update->move_right();
break;
}
case Qt::Key_Right:
{ m_update->move_left();
break;
}
}
}
Thanks again!
Your choice of QGraphicsView isn't very fortunate.
Basically, when you are implementing some custom painted graphical item (the graphic area of the game is this), you should create your own widget and simply implement the QWidget::keyPressEvent() method.
Related
i need to draw a ellipse and after some delay draw another one.
I having trouble doing this.
This is a simplified version of the code that i'm actually doing, but i belive this will help me solve the problem
here is the code.
MyView::MyView()
{
sc = new QGraphicsScene();
this->setSceneRect(0,0,800,600);
this->setFixedSize(800,600);
this->setStyleSheet("QScrollBar {height:0px;}");
this->setStyleSheet("QScrollBar {width:0px;}");
sc->setSceneRect(0,0,800,600);
this->setScene(sc);
}
void MyView::mousePressEvent(QMouseEvent *event)
{
sc->addEllipse(event->x(),event->y(),10,10,QPen(),QBrush(Qt::red));
int i=0;
while(i < 1000000000) // SIMULATING DELAY
i++; //
sc->addEllipse(event->y(),event->x(),10,10,QPen(),QBrush(Qt::blue));
}
class MyView : public QGraphicsView
{
public:
MyView();
QGraphicsScene *sc;
public slots:
void mousePressEvent(QMouseEvent *event);
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MyView wv;
wv.show();
return a.exec();
}
the first ellipse is not showing up until the while over and the second one appears
it's doesn't matter how long is the while. Always draw the two ellipses at the same time.
In the main thread of the GUI you should not have tasks that take too much time since they block the eventloop preventing the GUI's own work from being performed. In your case, that while loop can be replaced by a QTimer:
void MyView::mousePressEvent(QMouseEvent *event)
{
QPointF p = mapToScene(event->pos());
sc->addEllipse(QRectF(p, QSizeF(10, 10)), QPen(), QBrush(Qt::red));
// 1000 is the delay in ms
QTimer::singleShot(1000, this, [this, p](){
sc->addEllipse(QRectF(p, QSizeF(10, 10)), QPen(), QBrush(Qt::blue));
});
}
Is it possible to prevent right-click from opening the default context menu on QGraphicsTextItem ? The menu with "Undo, Redo, Cut, Copy, Paste..". On Ubuntu 18.04, that is. I don't know how this behaves on Windows.
I have overridden the mouse press handler to eat right-clicks in my view and tried to do that also in the item class itself. This actually did prevent the menu on Qt 5.10.0, but for some reason not anymore on 5.11.1:
void EditorView::mousePressEvent(QMouseEvent * event)
{
if (event->button() == Qt::RightButton)
{
return;
}
...
doOtherHandlingStuff();
...
}
In the item itself it doesn't have any effect if I do this:
void TextEdit::mousePressEvent(QGraphicsSceneMouseEvent * event)
{
event->ignore();
return;
}
You have to override the contextMenuEvent method of QGraphicsTextItem:
#include <QtWidgets>
class GraphicsTextItem: public QGraphicsTextItem
{
public:
using QGraphicsTextItem::QGraphicsTextItem;
protected:
void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override
{
event->ignore();
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene scene;
QGraphicsView w{&scene};
auto it = new GraphicsTextItem("Hello World");
it->setTextInteractionFlags(Qt::TextEditable);
scene.addItem(it);
w.show();
return a.exec();
}
Something is fundamentally wrong with my eventFilter, as it lets every single event through, while I want to stop everything. I've read lots of documentation on QEvent, eventFilter() and so on, but obviously I'm missing something big. Essentially, I'm trying to create my own modal-functionality for my popup-window class based on QDialog. I want to implement my own since the built-in setModal(true) includes a lot of features, e.g. playing QApplication::Beep(), that I want to exclude. Basically, I want to discard all events going to the QWidget (window) that created my popup. What I have so far is,
// popupdialog.h
#ifndef POPUPDIALOG_H
#define POPUPDIALOG_H
#include <QDialog>
#include <QString>
namespace Ui {class PopupDialog;}
class PopupDialog : public QDialog
{
Q_OBJECT
public:
explicit PopupDialog(QWidget *window=0, QString messageText="");
~PopupDialog();
private:
Ui::PopupDialog *ui;
QString messageText;
QWidget window; // the window that caused/created the popup
void mouseReleaseEvent(QMouseEvent*); // popup closes when clicked on
bool eventFilter(QObject *, QEvent*);
};
...
// popupdialog.cpp
#include "popupdialog.h"
#include "ui_popupdialog.h"
PopupDialog::PopupDialog(QWidget *window, QString messageText) :
QDialog(NULL), // parentless
ui(new Ui::PopupDialog),
messageText(messageText),
window(window)
{
ui->setupUi(this);
setAttribute(Qt::WA_DeleteOnClose, true); // Prevents memory leak
setWindowFlags(Qt::Window | Qt::FramelessWindowHint);
ui->message_text_display->setText(messageText);
window->installEventFilter(this);
//this->installEventFilter(window); // tried this also, just to be sure ..
}
PopupDialog::~PopupDialog()
{
window->removeEventFilter(this);
delete ui;
}
// popup closes when clicked on
void PopupDialog::mouseReleaseEvent(QMouseEvent *e)
{
close();
}
Here's the problem, the filter doesn't work. Note that if I write a std::cout
inside the if(...), I see that it does trigger whenever events are sent to window, it just doesn't stop them.
bool PopupDialog::eventFilter(QObject *obj, QEvent *e)
{
if( obj == window )
return true; //should discard the signal (?)
else
return false; // I tried setting this to 'true' also without success
}
When the user interacts with the main program, a PopupDialog can be created like this:
PopupDialog *popup_msg = new PopupDialog(ptr_to_source_window, "some text message");
popup_msg->show();
// I understand that naming the source 'window' might be a little confusing.
// I apologise for that. The source can in fact be any 'QWidget'.
Everything else works as expected. Only the event filter fails. I want the filter to remove events sent to the window that created the popup; like mouse clicking and key pressing, until the popup is closed. I'm expecting to be extremely embarrassed when someone points out a trivial fix in my code.
You have to ignore all events that arrive in the widget tree of the window. Therefore, you need to install the eventFilter application-wide and check, if the object you are filtering on is a descendant of window. In other words: Replace
window->installEventFilter(this);
by
QCoreApplication::instance()->installEventFilter(this);
and implement the event filter function this way:
bool PopupDialog::eventFilter(QObject *obj, QEvent *e)
{
if ( !dynamic_cast<QInputEvent*>( event ) )
return false;
while ( obj != NULL )
{
if( obj == window )
return true;
obj = obj->parent();
}
return false;
}
I tried it, tested it and it worked for me.
Note: Using event filters in Qt is a bit messy in my experience, since it is not quite transparent what is happening. Expect bugs to pop up from time to time. You may consider disabling the main window instead, if you and your clients don't have a problem with the grayed-out main window as a consequence.
After the massive amount of responses, feedback, suggestions and time ivested in extensive research I've finally found what I believe to be the optimal, and safest solution. I wish to express my sincere gratidtude to everyone for their aid to what Kuba Ober describes as "(...) not as simple of a problem as you think".
We want to filter out all certain events from a widget, including its children. This is difficult, because events may be caught in the childrens default eventfilters and responded to, before they are caught and filtered by the the parent's custom filter for which the programmer implements. The following code solves this problem by installing the filter on all children upon their creation. This example assumes the use of Qt Creator UI-forms and is based on the following blog post: How to install eventfilters for all children.
// The widget class (based on QMainWindow, but could be anything) for
// which you want to install the event filter on, includings its children
class WidgetClassToBeFiltered : public QMainWindow
{
Q_OBJECT
public:
explicit WidgetClassToBeFiltered(QWidget *parent = 0);
~WidgetClassToBeFiltered();
private:
bool eventFilter(QObject*, QEvent*);
Ui::WidgetClassToBeFiltered *ui;
};
...
WidgetClassToBeFiltered::WidgetClassToBeFiltered(QWidget *parent) :
QMainWindow(parent), // Base Class constructor
ui(new Ui::WidgetClassToBeFiltered)
{
installEventFilter(this); // install filter BEFORE setupUI.
ui->setupUi(this);
}
...
bool WidgetClassToBeFiltered::eventFilter(QObject *obj, QEvent* e)
{
if( e->type() == QEvent::ChildAdded ) // install eventfilter on children
{
QChildEvent *ce = static_cast<QChildEvent*>(e);
ce->child()->installEventFilter(this);
}
else if( e->type() == QEvent::ChildRemoved ) // remove eventfilter from children
{
QChildEvent *ce = static_cast<QChildEvent*>(e);
ce->child()->removeEventFilter(this);
}
else if( (e->type() == QEvent::MouseButtonRelease) ) // e.g. filter out Mouse Buttons Relases
{
// do whatever ..
return true; // filter these events out
}
return QWidget::eventFilter( obj, e ); // apply default filter
}
Note that this works, because the eventfilter installs itself on added children! Hence, it should also work without the use of UI-forms.
Refer this code to filter out specific event:-
class MainWindow : public QMainWindow
{
public:
MainWindow();
protected:
bool eventFilter(QObject *obj, QEvent *ev);
private:
QTextEdit *textEdit;
};
MainWindow::MainWindow()
{
textEdit = new QTextEdit;
setCentralWidget(textEdit);
textEdit->installEventFilter(this);
}
bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
if (obj == textEdit) {
if (event->type() == QEvent::KeyPress) {
QKeyEvent *keyEvent = static_cast<QKeyEvent*>(event);
qDebug() << "Ate key press" << keyEvent->key();
return true;
} else {
return false;
}
} else {
// pass the event on to the parent class
return QMainWindow::eventFilter(obj, event);
}
}
If you want to set more specific event filter on multiple widgets you can refer following code:
class KeyPressEater : public QObject
{
Q_OBJECT
protected:
bool eventFilter(QObject *obj, QEvent *event);
};
bool KeyPressEater::eventFilter(QObject *obj, QEvent *event)
{
if (event->type() == QEvent::KeyPress) {
QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
qDebug("Ate key press %d", keyEvent->key());
return true;
} else {
// standard event processing
return QObject::eventFilter(obj, event);
}
}
KeyPressEater *keyPressEater = new KeyPressEater(this);
QPushButton *pushButton = new QPushButton(this);
pushButton->installEventFilter(keyPressEater);
I'm learning to use Qt and I want to extend the Terminal Example of Qt. I want to use its console.cpp in a QWidget from de Containers tab in the Design editor.
In the Terminal Example of Qt, this class is used like this:
ui->setupUi(this);
console = new Console;
console->setEnabled(false);
setCentralWidget(console);
But as I want to use it in a smaller QWidget I don't know how to set it, which method can I use as equivalent of setCentralWidget for my QWidget? Image of the Design tab with the widget I want to set to the QWidget class
Can I also use the same QWidget in several tabs?
The console.cpp code is the following one.
#include "console.h"
#include <QScrollBar>
#include <QtCore/QDebug>
Console::Console(QWidget *parent)
: QPlainTextEdit(parent)
, localEchoEnabled(false)
{
document()->setMaximumBlockCount(100);
QPalette p = palette();
p.setColor(QPalette::Base, Qt::black);
p.setColor(QPalette::Text, Qt::green);
setPalette(p);
}
void Console::putData(const QByteArray &data)
{
insertPlainText(QString(data));
QScrollBar *bar = verticalScrollBar();
bar->setValue(bar->maximum());
}
void Console::setLocalEchoEnabled(bool set)
{
localEchoEnabled = set;
}
void Console::keyPressEvent(QKeyEvent *e)
{
switch (e->key()) {
case Qt::Key_Backspace:
case Qt::Key_Left:
case Qt::Key_Right:
case Qt::Key_Up:
case Qt::Key_Down:
break;
default:
if (localEchoEnabled)
QPlainTextEdit::keyPressEvent(e);
emit getData(e->text().toLocal8Bit());
}
}
void Console::mousePressEvent(QMouseEvent *e)
{
Q_UNUSED(e)
setFocus();
}
void Console::mouseDoubleClickEvent(QMouseEvent *e)
{
Q_UNUSED(e)
}
void Console::contextMenuEvent(QContextMenuEvent *e)
{
Q_UNUSED(e)
}
The Qt Example is this one: http://doc.qt.io/qt-5/qtserialport-terminal-example.html
Thanks so much!
If you're wanting to add it via designer just promote the QWidget that you added in your screegrab. (Right click > "Promote to..." > Fill in name & path to the console header).
Or not using promotion, you can add the console to a layout in code :
Console* console = new Console();
ui->your_layout_name_here->addWidget( console );
I am currently able to load my image into a grahpics scene, and then again into a QGraphicsViewer.
I am able to implement a zoom feature by dtecting a QEvent::Wheel and then calling the graphicsViews's scale() function.
However, I can't seem to figure out how to get the pan functionality working. I basically want to detect when a mouse has clicked down on the image, and then move the image left, right, up or down along with the mouse.
As of right now, I basically have a MouseFilter class that is detecting events, and doing different things depending on the event type. I attached that listener to the QGraphicsView object
In case someone is wondering how to do it on their own, it's actually quite simple. Here's the code from my app:
class ImageView : public QGraphicsView
{
public:
ImageView(QWidget *parent);
~ImageView();
private:
virtual void mouseMoveEvent(QMouseEvent *event);
virtual void mousePressEvent(QMouseEvent *event);
virtual void mouseReleaseEvent(QMouseEvent *event);
bool _pan;
int _panStartX, _panStartY;
};
You need to store the start position of the drag, for example like this (I used the right button):
void ImageView::mousePressEvent(QMouseEvent *event)
{
if (event->button() == Qt::RightButton)
{
_pan = true;
_panStartX = event->x();
_panStartY = event->y();
setCursor(Qt::ClosedHandCursor);
event->accept();
return;
}
event->ignore();
}
Also, you need to clear the flag and restore the cursor once the button is released:
void ImageView::mouseReleaseEvent(QMouseEvent *event)
{
if (event->button() == Qt::RightButton)
{
_pan = false;
setCursor(Qt::ArrowCursor);
event->accept();
return;
}
event->ignore();
}
To actually manage the drag, you need to override the mouse move event. QGraphicsView inherits a QAbstractScrollArea, and its scrollbars are easily accessible. You also need to update the pan position:
void ImageView::mouseMoveEvent(QMouseEvent *event)
{
if (_pan)
{
horizontalScrollBar()->setValue(horizontalScrollBar()->value() - (event->x() - _panStartX));
verticalScrollBar()->setValue(verticalScrollBar()->value() - (event->y() - _panStartY));
_panStartX = event->x();
_panStartY = event->y();
event->accept();
return;
}
event->ignore();
}
QGraphicsView has build-in mouse-panning support. Set correct DragMode and it will handle the rest. You do need the enable scroll bars for that to work.
neuviemeporte solution requires to subclass a QGraphicsView.
Another working drag implementation can be obtained without subclassing the view using eventFilter. If you don't need to customize other behaviors of the QGraphicsView, this technique will save you some work.
Let's say your GUI logic is maintained by a QMainWindow subclass and the QGraphicsView & QGraphicsScene are declared as a private members of this subclass. You would have to implement the eventFilter function as follows:
bool MyMainWindow::eventFilter(QObject *obj, QEvent *event)
{
if (obj == scene && event->type() == Event::GraphicsSceneMouseMove)
{
QGraphicsSceneMouseEvent *m = static_cast<QGraphicsSceneMouseEvent*>(event);
if (m->buttons() & Qt::MiddleButton)
{
QPointF delta = m->lastScreenPos() - m->screenPos();
int newX = view->horizontalScrollBar()->value() + delta.x();
int newY = view->verticalScrollBar()->value() + delta.y();
view->horizontalScrollBar()->setValue(newX);
view->verticalScrollBar()->setValue(newY);
return true;
}
}
return QMainWindow::eventFilter(obj, event);
}
To filter events from the QGraphicsScene, you'll have to install MyMainWindow as an eventFilter of the scene. Perhaps you could do this in the same function where you setup your GUI.
void MyMainWindow::setupGUI()
{
// along with other GUI stuff...
scene->installEventFilter(this);
}
You can extend this idea to replace the cursor with the drag "hand" as previously shown.