Draw a point when button is clicked
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So, I created 2 functions: onClick() - function that executes when the button is clicked, and drawPoint(int x,int y).
onClick function calls the drawPoint function with x and y parameters, but when I run the program, and I click the button, it says:
"QPainter::drawPoints: Painter not active".
Here's my mainwindow.cpp:#include "mainwindow.h" #include "ui_mainwindow.h" MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) , ui(new Ui::MainWindow) { ui->setupUi(this); QPushButton *button = QMainWindow::findChild<QPushButton *>("pushButton"); connect(button, SIGNAL(released()), SLOT(onClick())); } MainWindow::~MainWindow() { delete ui; } void MainWindow::drawPoint(int x, int y) { QPainter painter; painter.drawPoint(x,y); } void MainWindow::onClick() { QPoint point = QCursor::pos(); int x = point.x(); int y = point.y(); drawPoint(x,y); }I'm a total beginner in Qt, and have no idea what's going on. I've searched on this forum, but I couldn't find anything.
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So, I created 2 functions: onClick() - function that executes when the button is clicked, and drawPoint(int x,int y).
onClick function calls the drawPoint function with x and y parameters, but when I run the program, and I click the button, it says:
"QPainter::drawPoints: Painter not active".
Here's my mainwindow.cpp:#include "mainwindow.h" #include "ui_mainwindow.h" MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) , ui(new Ui::MainWindow) { ui->setupUi(this); QPushButton *button = QMainWindow::findChild<QPushButton *>("pushButton"); connect(button, SIGNAL(released()), SLOT(onClick())); } MainWindow::~MainWindow() { delete ui; } void MainWindow::drawPoint(int x, int y) { QPainter painter; painter.drawPoint(x,y); } void MainWindow::onClick() { QPoint point = QCursor::pos(); int x = point.x(); int y = point.y(); drawPoint(x,y); }I'm a total beginner in Qt, and have no idea what's going on. I've searched on this forum, but I couldn't find anything.
@mitrovicl
You can only draw a point in a paint event.Basically, can you pick something different from this to do? Widget applications are not usually about drawing points. Depends what you are ultimately trying to achieve.
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@mitrovicl
You can only draw a point in a paint event.Basically, can you pick something different from this to do? Widget applications are not usually about drawing points. Depends what you are ultimately trying to achieve.
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@JonB Thanks for the answer, I'm trying to create CPS (Clicks per second) test. And I want every click to leave a "trail". I'll look into pain events.
@mitrovicl
Maybe you might be interested in examples which come with Qt:Search for
paintEventin them. -
Hi and welcome to devnet,
The first thing: you cannot paint on a widget outside the paint event.
Second, please read the QPainter documentation. It provides a lot of information as well as links to various examples.
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So, I created 2 functions: onClick() - function that executes when the button is clicked, and drawPoint(int x,int y).
onClick function calls the drawPoint function with x and y parameters, but when I run the program, and I click the button, it says:
"QPainter::drawPoints: Painter not active".
Here's my mainwindow.cpp:#include "mainwindow.h" #include "ui_mainwindow.h" MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) , ui(new Ui::MainWindow) { ui->setupUi(this); QPushButton *button = QMainWindow::findChild<QPushButton *>("pushButton"); connect(button, SIGNAL(released()), SLOT(onClick())); } MainWindow::~MainWindow() { delete ui; } void MainWindow::drawPoint(int x, int y) { QPainter painter; painter.drawPoint(x,y); } void MainWindow::onClick() { QPoint point = QCursor::pos(); int x = point.x(); int y = point.y(); drawPoint(x,y); }I'm a total beginner in Qt, and have no idea what's going on. I've searched on this forum, but I couldn't find anything.
@mitrovicl said in Draw a point when button is clicked:
QPushButton *button = QMainWindow::findChild<QPushButton *>("pushButton");
I assume you have a
mainWindow.ui(modified with QtDesigner), then this is not necessary.
Just access you button by using youruipointer.ui->pushButtonconnect(button, SIGNAL(released()), SLOT(onClick()));
and better use the updated, Qt5 function-based "Signal & Slot"-syntax.
connect(ui->pushButton, &QPushButton::released, this, &MainWindow::onClick); -
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