suitable class for plotting pixels

[Uwe]

unfortunately i got stuck in the first try .

Your code tries to paint a polygon, what is something very different than plotting pixels ( for what you got answers ).
Maybe it's better to go one step back and explain more detailed, what your "pixels" are and how do you want to display them.

Do you want to display something like curves in a diagram ?

Uwe

[babu198649]

ok ume i explain in detail
i have an array of size[360*250] .it represents the degrees of a circle and radius.(for each corresponding degree and radius i have a value in the matrix.)

based on the value in the matrix i have to represent the circle(at every degree and radius) in different color.

so i made a polygon (the area between the angles and a unit radius) and colouring the circle based on the value in the matrix.

thus i need to fill the polygon with different color after computing the polygon coordinates.

[high_flyer]

have an array of size[360*250] .it represents the degrees of a circle and radius.(for each corresponding degree and radius i have a value in the matrix.)

Do you mean you have a matrix of 250 circles?

based on the value in the matrix i have to represent the circle(at every degree and radius) in different color.

By represent, do you mean draw?
and what do you mean with "at every degree and radius"?
A circle has a radius, and all the degrees in it....

so i made a polygon (the area between the angles and a unit radius) and colouring the circle based on the value in the matrix.

here I lost you completely...
Why don't you use QPainter::drawEllipse()?
And set the brush with the color you want?

You might want to have a look at QPainter::drawChord() and QPainter::drawPie() too

[babu198649]

Do you mean you have a matrix of 250 circles?

No

i have only one circle , the circle is divided in to [360]*[250] parts which i called it as matrix.

for every value in matrix representing the circle in different color .

so dividing the circle in to polygons(360*250 polygons) and filling the polygons with different colors.

after finding the points of every polygon i fill the polygon(this is where i got struck) ,before finding the points for the next.

finding the polygon values occur in the loops.

[babu198649]

do i definitely need to reimplement the paintEvent() function.

[high_flyer]

Oh ok I see. (sorry for being the slow one)
Then I join wysota and Uwe - QPainter::drawPie().

[babu198649]

thanks for all of u r cooperation .

even though i am drawing a circle i have an algorithm that has four points and i should definitely need the polygon function.

but is there any way to draw polygon on QWidget without using paintEvent function.

[wysota]

No, there is none.

You want to obtain something like in the attachment (it draws lines instead of polygons, but the idea is similar)?

#include <QWidget>
#include <QPainter>
#include <QPaintEvent>
#include <QApplication>
 
class Widget : public QWidget {
public:
Widget() : QWidget(){
  for(int i=0;i<360;i++){
    data[i].c = QColor(qrand()%256, qrand()%256, qrand()%256);
    data[i].r = (qrand()%(1000*200))/1000.0;
  }
}
QSize sizeHint() const { return QSize(200,200); }
 
protected:
void paintEvent(QPaintEvent *){
  QPainter p(this);
  p.fillRect(rect(), Qt::white);
  for(int i=0;i<360;i++){
    p.save();
    p.translate(width()/2, height()/2);
    p.rotate(i);
    p.setPen(data[i].c);
    p.drawLine(QPointF(0,0), QPointF(data[i].r, 0));
    p.restore();
  }
}
private:
  struct S {
    QColor c;
    float r;
  };
  S data[360];
 
};
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  Widget w;
  w.show();
  return app.exec();
}

#include <QWidget>
#include <QPainter>
#include <QPaintEvent>
#include <QApplication>

class Widget : public QWidget {
public:
Widget() : QWidget(){
  for(int i=0;i<360;i++){
    data[i].c = QColor(qrand()%256, qrand()%256, qrand()%256);
    data[i].r = (qrand()%(1000*200))/1000.0;
  }
}
QSize sizeHint() const { return QSize(200,200); }

protected:
void paintEvent(QPaintEvent *){
  QPainter p(this);
  p.fillRect(rect(), Qt::white);
  for(int i=0;i<360;i++){
    p.save();
    p.translate(width()/2, height()/2);
    p.rotate(i);
    p.setPen(data[i].c);
    p.drawLine(QPointF(0,0), QPointF(data[i].r, 0));
    p.restore();
  }
}
private:
  struct S {
    QColor c;
    float r;
  };
  S data[360];

};

int main(int argc, char **argv){
  QApplication app(argc, argv);
  Widget w;
  w.show();
  return app.exec();
}

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[babu198649]

thank u wysota
i realize the pain u have taken to code the above program( this is the second time u r taking pain for me).
the problem was with save() and restore(). initiallly i have not used these functions.

at first i followed the Basic Drawing Example and i have not noticed the save() and restore() function.
i should have been careful while reading docs to save u the pain

thanks again

[Uwe]

based on the value in the matrix i have to represent the circle(at every degree and radius) in different color.

Ok, then forgot all you read about QImage and QPixmap.

I recommend to follow Witolds suggestion and use a simple QWidget ( QGraphicsView is pointless overhead here, that gives you more trouble than solution ). Then use QPainter::drawArc ( or drawPie ? )

HTH,
Uwe