I don't have much experience with Qt and I am having trouble using QPainter.
I am trying to make a simple graphing widget which takes in a number of points and to create a QVector of QPoints, and then uses this vector to draw a polygon. However, nothing is appearing right now with my implementation. I am fairly certain that I have added the widget correctly to the window, as I can see the empty space it should occupy. This leads me to believe the problem to be in the graphing widget.
Any assistance is appreciated.
header:
//graph.h
#ifndef GRAPH_H
#define GRAPH_H
#include <QWidget>
#include <QPainter>
#include <QVector>
class Graph : public QWidget
{
Q_OBJECT
public:
Graph(QWidget *parent = 0);
QSize minimumSizeHint() const;
QSize maximumSizeHint() const;
QSize sizeHint() const;
void addPoint(int w, int h);
void clearPoints();
void drawGraph();
protected:
void paintEvent(QPaintEvent *event);
private:
QPen pen;
QBrush brush;
QPixmap pixmap;
QVector<QPoint> points;
};
#endif // GRAPH_H
source:
//graph.cpp
#include "graph.h"
Graph::Graph(QWidget *parent)
: QWidget(parent)
{
points.resize(0);
setBackgroundRole(QPalette::Base);
setAutoFillBackground(true);
}
void Graph::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.setPen(QPen(Qt::NoPen));
painter.setBrush(QBrush(Qt::green, Qt::SolidPattern));
painter.setRenderHint(QPainter::Antialiasing, true);
painter.drawPolygon(points);
}
QSize Graph::minimumSizeHint() const
{
return sizeHint();
}
QSize Graph::maximumSizeHint() const
{
return sizeHint();
}
QSize Graph::sizeHint() const
{
return QSize(500, 200);
}
void Graph::addPoint(int w, int h)
{
points.append(QPoint(w*2, h*2));
}
void Graph::clearPoints()
{
points.clear();
}
void Graph::drawGraph() {
points.prepend(QPoint(0,0)); //The base points of the graph
points.append(QPoint(500,0));
update();
points.clear();
}
In drawGraph(), the call to update() posts an event notifying the widget to paint itself. You then clear the points and the drawGraph() call exits. After that, the event loop will process the update event and trigger a call to the paintEvent() but by then, there are no points in the vector of points to paint.
Don't think of the paintEvent() as painting something permanent onto the widget once that will be displayed forever until you clear it and paint something else. The paintEvent() needs to be able to paint the widget from scratch whenever it needs to be redrawn. This is often due to a request from the system when the widget is moved, minimized and restored etc. This means your vector of points needs to remain until you no longer want a polygon to be displayed or the points are changed.
It looks like you might be adding only two points to your points-list. I don't think it is possible to have a polygon with only two points; try adding a third point and see if you get a triangle.
Related
When re-implementing any mouse event function in a QGraphicsPixmapItem such as mousePressEvent, mouseReleaseEvent, mouseMoveEvent, the graphics item uses pixel-perfect collision. For example, for the mousePressEvent to be triggered, the mouse must be exactly on top of a visible pixel in the pixmap when clicked.
On the other hand, I want the collision to be a generalized box based on the pixmap's width and height: [0, 0, width, height].
How can this be accomplished?
(Some sample code cause people seem to like that):
class MyGraphicsItem: public QGraphicsPixmapItem {
public:
MyGraphicsItem(): QGraphicsPixmapItem() {}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent* event) {
// do stuff. Will be called when clicked exactly on the image
QGraphicsPixmapItem::mousePressEvent(event);
}
}
Thanks to SteakOverflow for a point in the right direction.
Aiiright, here's what you gotta do:
class MyGraphicsItem: public QGraphicsPixmapItem {
public:
MyGraphicsItem(): QGraphicsPixmapItem() {
// Change shape mode in constructor
setShapeMode(QGraphicsPixmapItem::BoundingRectShape);
}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent* event) {
// do stuff. Will be called when clicked exactly on the image
QGraphicsPixmapItem::mousePressEvent(event);
}
}
Alternatively, you can do:
class MyGraphicsItem: public QGraphicsPixmapItem {
public:
MyGraphicsItem(): QGraphicsPixmapItem() {}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent* event) {
// do stuff. Will be called when clicked exactly on the image
QGraphicsPixmapItem::mousePressEvent(event);
}
// ::shape defines collision.
// This will make it a rect based on general dimensions of the pixmap
QPainterPath shape() const {
if(!pixmap().isNull()) {
QPainterPath path;
path.addRect(0, 0, pixmap().width(), pixmap().height());
return path;
} else {
return QGraphicsPixmapItem::shape();
}
}
}
I am doing a project in Qt and there is an object QPainter which is declared as :
QPainter painter(this);
Where this points to the present class. My problem is that I need to declare this object such that it is accessible to the entire class functions.
If I declare it inside the constructor then its scope is not valid for other functions, and I cannot declare outside all function in my .cpp file as this variable doesn't make any sense.
So how can I declare my object such that it is accessible to all the functions?
Edit : Painter Code :
void MainWindow :: paintEvent(QPaintEvent * e)
{
QMainWindow::paintEvent(e);
if(1)
{
QPainter painter(this);
QPen paintpen(Qt::red);
paintpen.setWidth(5);
QPoint p1;
p1.setX(mFirstX);
p1.setY(mFirstY);
painter.setPen(paintpen);
painter.drawPoint(p1);
}
}
Mouse Event Code :
void MainWindow :: mousePressEvent(QMouseEvent *e)
{
mFirstX=0;
mFirstY=0;
mFirstClick=true;
mpaintflag=false;
if(e->button() == Qt::LeftButton)
{
//store 1st point
if(1)
{
mFirstX = e->x();
mFirstY = e->y();
mFirstClick = false;
mpaintflag = true;
qDebug() << "First image's coordinates" << mFirstX << "," << mFirstY ;
update();
}
}
}
PROBLEM : I want to create the point but I don't want it to disappear from the widget(mainWindow). Here since the object is created during the paintEvent method each time the point that I am drawing is disappearing when the next point is drawn.
And if I declare it outside the paintEvent then I get the following error:
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setPen: Painter not active
In general, declaring the QPainter object globally is not a good idea. It is better to construct it in the QWidget::paintEvent (where it will be active) and, as #Mat said, pass it (by reference) to the functions that need it.
In your particular case the point disappears because the widget is redrawn, not because the QPainter is destroyed. So the strategy should be to create and manage a buffer of points. Add a point to the buffer in a mouse event, e.g. QWidget::mousePressEvent (there do some management too, e.g. limiting the number of points) and in the paint event - paint all the points from the buffer.
Here is an oversimplified example which could easily be adapted for your specific purpose:
MainWindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QMouseEvent>
#include <QPaintEvent>
#include <QPainter>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
protected:
void mousePressEvent(QMouseEvent *event);
void paintEvent(QPaintEvent *event);
private:
QList<QPoint> m_points;
};
#endif // MAINWINDOW_H
MainWindow.cpp
#include "MainWindow.h"
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
QPalette p = QPalette();
p.setColor(QPalette::Window, Qt::white);
setPalette(p);
setAutoFillBackground(true);
resize(400, 400);
}
void MainWindow::mousePressEvent(QMouseEvent *event)
{
m_points.append(event->pos());
update();
}
void MainWindow::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.setClipping(true);
painter.setClipRect(event->rect());
painter.setPen(QPen(Qt::red, 5));
foreach (QPoint point, m_points) { painter.drawPoint(point); }
}
That's what class attributes are for :
class MyObject : public QObject {
Q_OBJECT
public:
MyObject(QObject *parent = 0) : QObject(parent), painter_(this) {
// Other things if you need them
}
void aFunction() {
// You can use painter_ here !!
}
private :
QPainter painter_;
}
In the private access specifier of your main window class in mainWindow.h, you could write this line
QPainter *painterPointer
creating a pointer accessible in all MainWindow slots. You could use that painterPointer as though it were any painter pointer initialised in any slot. However if you wanted to use this pointer in a developer defined function or method outside of the MainWindow class, you would have to pass the pointer as a reference (or pointer to the pointer).
might have to include a line similar to this in the MainWindow Constructor
painterPointer = new QPainter(this);
I want to make one QGraphicsItem in a QGraphicsScene move (or change size) when another one moves. But, trying to access either QGraphicsItem from the QGraphicsScene object causes crashes.
Here's a dummy example. I want to automatically:
Resize BlueItem's width when I click and drag RedItem.
Move RedItem when I click and drag BlueItem.
The dummy code:
redItem.h (A pixmap item)
#include <QGraphicsPixmapItem>
class RedItem : public QGraphicsPixmapItem
{
public:
RedItem();
protected:
void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
};
redItem.cpp
RedItem::RedItem()
{
setPixmap(QPixmap(redPixMap));
setFlags(ItemIsMovable);
setCacheMode(DeviceCoordinateCache);
}
void RedItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
setPos(event->scenePos(),0); //I can override this part just fine.
}
blueItem.h (A resizable rectangle item)
#include <QGraphicsRectItem>
class BlueItem : public QGraphicsRectItem
{
public:
BlueItem();
protected:
void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
};
blueItem.cpp is similar to redItem.cpp
graphicsViewWidget.h (The GraphicsView)
#include <QGraphicsView>
#include "blueItem.h"
#include "redItem.h"
class GraphicsViewWidget : public QGraphicsView
{
Q_OBJECT
public:
explicit GraphicsViewWidget(QWidget *parent = 0);
protected:
virtual void mouseMoveEvent(QMouseEvent *event);
private:
RedItem *red;
BlueItem *blue;
};
graphicsViewWidget.cpp
#include "graphicsViewWidget.h"
#include <QRectF>
void Qx::createItem(int frame)
{
red = new RedItem;
red->setPos(0, 0);
scene()->addItem(red);
blue = new BlueItem;
blue->setPos(10, 10);
scene()->addItem(blue);
}
void GraphicsViewWidget::mouseMoveEvent(QMouseEvent *event) //QGraphicsSceneMouseEvent
{
QGraphicsView::mouseMoveEvent(event);
//if(redItem moves)
// resize blueItem;
//if(blueItem moves)
// move redItem;
}
Any help or advice would be greatly appreciated.
If you make item B a child of item A, then it will live in its coordinate space. This means all transformations - moving, scaling, rotating... everything you apply to the parent item will also be applied to all its children and their children and so on...
I have some project where I'm interested in using of QML ui.
But it is not enough for us to use standart Qt rendering sistem, I must try to repaint all ui elements every frame, not only in QCoreApplication::processEvents().
It's requered because it is some DirectX render in background of ui.
In this case I found the way to render widgets only using QWidget::render() function, but this method uses CPU instead of GPU, so it is too slow and is't correct at all.
So, what I have:
I have QApplication integrated into my application's loop.
Signals/Slots system works fine and process events is called right
way.
Own render system with DirectX11, that i use to render other
graphics.
I need redraw (update) qt (QML) ui every frame using
DirectX, or maybe angle, but every frame of render.
Already existing code example:
In this example reimplemented widget is app's main window and used like context of DirectX render.
header:
#ifndef _QTD3DCONTEXTWIDGET_
#define _QTD3DCONTEXTWIDGET_
#include <QtWidgets/QWidget>
#include <QtQuick/QQuickView>
#include <QtQuickWidgets/QQuickWidget>
#include <QtQml/qqml.h>
#include <QtWidgets/QPushButton>
#include <QtGui/QPaintEngine>
#include <QtGui/QPaintDevice>
class QtGfxPaintEngine : public QPaintEngine
{
public:
QtGfxPaintEngine(PaintEngineFeatures caps = PaintEngineFeatures());
virtual bool begin(QPaintDevice *pdev);
virtual bool end();
//virtual void drawEllipse(const QRectF &rect);
//virtual void drawEllipse(const QRect &rect);
virtual void drawImage(const QRectF &rectangle,
const QImage &image,
const QRectF &sr,
Qt::ImageConversionFlags flags = Qt::AutoColor);
virtual void drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF &sr);
virtual void drawPoints(const QPointF *points, int pointCount);
virtual void drawPolygon(const QPointF *points, int pointCount, PolygonDrawMode mode);
virtual void drawRects(const QRectF *rects, int rectCount);
virtual void drawTextItem(const QPointF &p, const QTextItem &textItem);
virtual void drawTiledPixmap(const QRectF &rect, const QPixmap &pixmap, const QPointF &p);
// default implementation used
//virtual void drawLines(const QLineF *lines, int lineCount); //not
//virtual void drawLines(const QLine *lines, int lineCount);
//virtual void drawPath(const QPainterPath &path);
//virtual void drawPoints(const QPoint *points, int pointCount);
//virtual void drawPolygon(const QPoint *points, int pointCount, PolygonDrawMode mode);
//virtual void drawRects(const QRect *rects, int rectCount);
virtual Type type() const;
virtual void updateState(const QPaintEngineState &newState);
private:
int getClosestPowOfTwo(QSize& size);
};
class QtD3DContextWidget : public QWidget
{
Q_OBJECT
public:
QtD3DContextWidget(QWidget* parent = nullptr);
virtual ~QtD3DContextWidget() = default;
virtual QPaintEngine* paintEngine() const;
virtual void paintEvent(QPaintEvent* event);
void mousePressEvent(QMouseEvent *event) override;
QQuickWidget* containerWidget;
QPushButton* widg;
QtGfxPaintEngine* mPaintEngine;
private:
};
#endif // !_QTD3DCONTEXTWIDGET_
cpp, without draw functions (they are implemented with DirectX and works fine):
QtD3DContextWidget::QtD3DContextWidget(QWidget* parent /*= nullptr*/)
: QWidget(parent, Qt::MSWindowsOwnDC)
{
mPaintEngine = new QtGfxPaintEngine(QPaintEngine::AllFeatures);
QApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
setAttribute(Qt::WA_NativeWindow, true);
setAttribute(Qt::WA_TranslucentBackground, true);
setAttribute(Qt::WA_UpdatesDisabled, true);
setAttribute(Qt::WA_TransparentForMouseEvents);
setAttribute(Qt::WA_NoSystemBackground, true);
setAttribute(Qt::WA_OpaquePaintEvent, true);
containerWidget = new QQuickWidget(this);
containerWidget->setAttribute(Qt::WA_TranslucentBackground, true);
containerWidget->setAttribute(Qt::WA_OpaquePaintEvent, true);
containerWidget->setAttribute(Qt::WA_NoSystemBackground, true);
containerWidget->setClearColor(Qt::transparent);
QString sourceUi = QCoreApplication::applicationDirPath() + "/qtui/test.qml";
containerWidget->setSource(QUrl::fromLocalFile(sourceUi));
containerWidget->move(0, 0);
resize(1280, 720);
widg = new QPushButton("test", this);
//widg->setBackgroundRole(QPalette::WindowText);
widg->resize(50, 50);
widg->move(600, 300);
widg->show();
show();
setVisible(true);
//wrapper->show();
}
QPaintEngine* QtD3DContextWidget::paintEngine() const
{
return mPaintEngine;
}
void QtD3DContextWidget::paintEvent(QPaintEvent* event)
{
}
QtGfxPaintEngine::QtGfxPaintEngine(PaintEngineFeatures caps /*= PaintEngineFeatures()*/)
: QPaintEngine(caps)
{}
QPaintEngine::Type QtGfxPaintEngine::type() const
{
return QPaintEngine::Direct3D;
}
void QtGfxPaintEngine::updateState(const QPaintEngineState &newState)
{}
and in render ui method:
QPainter painter(w);
painter.setBrushOrigin(w->containerWidget->pos());
w->containerWidget->render(&painter);// , w->widg->pos());// , w->widg->rect());// , QWidget::DrawChildren);
painter.end();
that's works fine but using CPU.
What i try it's to replace it with
w->repaint();
so entire widget is repainted, but not every frame, and in this case ui is "blinking" and widget try to repain it's background not as transparent, but with white color.
Or replace with
w->containerWidget->repaint();
and nothing is happends.
trying to call QApplication::process events just after w->repaint() don't make sence, as i can see.
and ofcourse i have comented setAttribute(Qt::WA_UpdatesDisabled, true); if i try to refresh widget in this manner.
PS: sorry for my english)))
If you want to render all Qt content through a central renderer then you might be better of implementing your own QPA (Qt Platform Abstraction) plugin, based on or derived from the normal Windows QPA plugin.
Then you can (a) handout your paint device implementation from there and not need any application side code and potentially use something like ANGLE to get the QtQuick scene graph rendered via Direct3D
I create class Widget, it creates window, this class paints something on the window (i.e. it works as I want).
I create yet one class, Circle, I want to paint on the window of class Widget.
I pass adress of Widget and try to paint on Widget using QPainter paint (address of Widget); (in the instance of Circle) but i don't see anything.
I've tried to make code as shorter as possible during the execution of program I type out address of object Widget. It doesn't change. It means that the address of Widget was passed right.
Everywhere, where I type out address of Widget I receive the same address. Here is the code:
header Widget
class Widget : public QWidget
{
public:
int mi,mcount;
Widget(QWidget *parent = 0);
QPaintEvent *ev;
virtual void paintEvent(QPaintEvent *);
void drawcircle();
};
Widget.cpp
Widget::Widget(QWidget *parent) : QWidget(parent)
{
QWidget::paintEvent(ev);
qDebug()<<this<<"\n"; //
}
void Widget::drawcircle()
{
QPainter paint(this);
paint.drawEllipse(0,0,100,100);
}
void Widget::paintEvent(QPaintEvent *ev)
{ this->drawcircle(); }
header Circle.h
class Circle :public QWidget
{
public:
Circle(Widget *widget); // i do trick here!!!
Widget *mwidg;
QPaintEvent *ev;
virtual void paintEvent(QPaintEvent *);
void drawcircle(Widget *mwidg);
};
Circle.cpp
Circle::Circle(Widget *widget)
{
qDebug()<<"circle widget"<<widget;
QWidget::paintEvent(ev);
mwidg=widget;
qDebug()<<"\n"<<mwidg;
}
void Circle::paintEvent(QPaintEvent *ev)
{ qDebug()<<"circle paintEvent mwidget"<<mwidg<<"\n";
this->drawcircle(mwidg);
}
void Circle::drawcircle(Widget *mwidg)
{
QPainter paint(mwidg);
paint.drawEllipse(20,10,40,40);
paint.drawLine(0,0,500,500);
}
main
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget *w=new Widget;
qDebug()<<"main address of widget"<<w<<"\n";
Circle *f=new Circle(w);
w->show();
return a.exec();
}
program is compiled and linked successful
What exactly are you trying to achieve? You can only paint on any widget in it's own paintEvent() handler, and you should not call paintEvent() yourself, it won't work. Also, get rid of the QPaintEvent member variables.
I would suggest that you make Circle a child of Widget, and then paint the circle from Circle::paintEvent(). Alternatively, use QGraphicsView.
well , thank you for your attempts to help
but all that i was needing:
this -> setParent(widget);
in costructor Circle::Circle, if somebody'll want to see my solve,one can see that figures are moved
source code is here source code