QLabel, QPainter, QMouseEvent, and Mapping
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Hello QT Family, I am working on an analysis system with a little bit of AI and ML implementation. I have a project that first opens a video and the user can play it. Upon a press of a button, it opens up another window and displays the frame that has been paused to allow user to draw lines using qmouse event. I then want to map the mouse events from the label on the popup window back to the video to help count items, cars, or people. I am currently having a challenge with drawing the lines. Here is the snippet of the code that draws the line.
myQLabel.h
#ifndef MYQLABEL_H
#define MYQLABEL_H#include <QObject>
#include <QWidget>
#include <QLabel>
#include <QMouseEvent>
#include <QEvent>
#include <QDebug>
#include <QPainter>
#include "debugger.h"
class myQLabel : public QLabel
{
Q_OBJECT
public:
explicit myQLabel(QWidget * parent = nullptr);
public:
void mousePressEvent(QMouseEvent* ev);
void mouseMoveEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);
public:
bool isMousePressed;
bool drawStarted;
bool isMouseMoving;
public:
int x, y;
int lineStartX;
int lineStartY;
int lineStopX;
int lineStopY;
public:QPainter painter; QPixmap mPix; QLine mLine; QRect mRect; QPixmap mpPix; void drawLine(); void drawRectangle(); QPoint pointOne; QPoint pointTwo; QLine counterLine;};
#endif // MYQLABEL_H
myQLabel.cpp
#include "myqlabel.h"myQLabel::myQLabel(QWidget* parent): QLabel(parent)
{
drawStarted = false;
}
void myQLabel::mousePressEvent(QMouseEvent *ev) {
lineStartX = this->x = ev->x();
lineStartY = this->y = ev->y();
QPoint startPoint(lineStartX, lineStartY);
counterLine.setP1(startPoint);}
void myQLabel::mouseMoveEvent(QMouseEvent *event) {
lineStopX = this->x = event->x();
lineStopY = this->y = event->y();
update();QPoint endPoint(lineStopX, lineStopY); counterLine.setP2(endPoint); QPixmap pix; if(this->pixmap() && !this->pixmap()->isNull()){ pix = this->pixmap()->copy(); }else{ pix = QPixmap(this->size()); } QPainter p(&pix); QPen pen(Qt::blue, 5, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin); p.setPen(pen); p.drawLine(counterLine); p.end(); this->setPixmap(pix); QLabel::mousePressEvent(event);}
void myQLabel::mouseReleaseEvent(QMouseEvent *event) {
}
I have promoted my label to myQLabel class. It works but seems to draw many lines and I believe the problem is in the paint event called in my mousemoveevent. Any help will be immensely appreciated. -
Hello QT Family, I am working on an analysis system with a little bit of AI and ML implementation. I have a project that first opens a video and the user can play it. Upon a press of a button, it opens up another window and displays the frame that has been paused to allow user to draw lines using qmouse event. I then want to map the mouse events from the label on the popup window back to the video to help count items, cars, or people. I am currently having a challenge with drawing the lines. Here is the snippet of the code that draws the line.
myQLabel.h
#ifndef MYQLABEL_H
#define MYQLABEL_H#include <QObject>
#include <QWidget>
#include <QLabel>
#include <QMouseEvent>
#include <QEvent>
#include <QDebug>
#include <QPainter>
#include "debugger.h"
class myQLabel : public QLabel
{
Q_OBJECT
public:
explicit myQLabel(QWidget * parent = nullptr);
public:
void mousePressEvent(QMouseEvent* ev);
void mouseMoveEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);
public:
bool isMousePressed;
bool drawStarted;
bool isMouseMoving;
public:
int x, y;
int lineStartX;
int lineStartY;
int lineStopX;
int lineStopY;
public:QPainter painter; QPixmap mPix; QLine mLine; QRect mRect; QPixmap mpPix; void drawLine(); void drawRectangle(); QPoint pointOne; QPoint pointTwo; QLine counterLine;};
#endif // MYQLABEL_H
myQLabel.cpp
#include "myqlabel.h"myQLabel::myQLabel(QWidget* parent): QLabel(parent)
{
drawStarted = false;
}
void myQLabel::mousePressEvent(QMouseEvent *ev) {
lineStartX = this->x = ev->x();
lineStartY = this->y = ev->y();
QPoint startPoint(lineStartX, lineStartY);
counterLine.setP1(startPoint);}
void myQLabel::mouseMoveEvent(QMouseEvent *event) {
lineStopX = this->x = event->x();
lineStopY = this->y = event->y();
update();QPoint endPoint(lineStopX, lineStopY); counterLine.setP2(endPoint); QPixmap pix; if(this->pixmap() && !this->pixmap()->isNull()){ pix = this->pixmap()->copy(); }else{ pix = QPixmap(this->size()); } QPainter p(&pix); QPen pen(Qt::blue, 5, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin); p.setPen(pen); p.drawLine(counterLine); p.end(); this->setPixmap(pix); QLabel::mousePressEvent(event);}
void myQLabel::mouseReleaseEvent(QMouseEvent *event) {
}
I have promoted my label to myQLabel class. It works but seems to draw many lines and I believe the problem is in the paint event called in my mousemoveevent. Any help will be immensely appreciated.@vinnadipo09 You should not draw in mouseMoveEvent. You should only call update() there and do the painting in paintEvent.
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@jsulm Thanks. I followed this https://forum.qt.io/topic/28902/solved-qmouseevent-qpainter-and-opencv/2 , after a long struggle and that is what I have implemented. I would appreciate any clear clarification from your end. I will implement it asap and get back to you on the outcome.
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@jsulm Thanks. I followed this https://forum.qt.io/topic/28902/solved-qmouseevent-qpainter-and-opencv/2 , after a long struggle and that is what I have implemented. I would appreciate any clear clarification from your end. I will implement it asap and get back to you on the outcome.
@vinnadipo09 said in QLabel, QPainter, QMouseEvent, and Mapping:
I would appreciate any clear clarification from your end
Not sure what clarification you need. In mouseMoveEvent store all data needed to paint in member variables and call update().
Take a look at https://doc.qt.io/qt-5/qpainter.html
"The common use of QPainter is inside a widget's paint event" -
Thanks. Let me work this out.
