Repaint() function paints only last point!!

onkar

@void Widget::paintEvent(QPaintEvent *eve){
QPainter p(this);
QPen pen(Qt::white,1,Qt::SolidLine);
p.setPen(pen);
if(f==1){
qDebug()<<x;
p.drawPoint(x,y);
f=0;
}

}

void Widget::func()
{
for(int i=0;i<100;i++){
f=1;
x++;
repaint();
qDebug()<<x;

}
@

JohanSolo

Hello and welcome to the forum!

AFAIK you should not call paintEvent so often. The loop on your points you have in your Widget::func method should rather be in the Widget::paintEvent method. But I have no clue if this will solve your problem.

SGaist

Hi and welcome to devnet,

As Johan said, calling repaint like that is a bad idea. If you want to animate the painting you should rather use e.g. a QTimer.

Also, you have to pay attention on the value of x, just incrementing it will make it larger than your widget.

onkar

The actual func() is line drawing algorithms,dda()
And bresenham(). I had written these functions in paintevent itself but the teacher told me to make separate functions.
Hence i had to call repaint().
The algorithm increments or decrements the global variables x and y according to the algorithm and i expect repaint to draw the points.
Hope i made my point clear.
Thank you

hskoglund

Hi, repaint() is usually called when you want to clean or refresh your widget's screen area, what I mean: you call "erase screen" 100 times and drawPoint() 100 times :-)

Best is to do what SGaist suggests,use a QTimer.

Or you can change your code in Widget::paintEvent() so that first time it's called it draws just one point; then next time it's called, redraw previous point and one more, next time draw 3 points etc.

SGaist

Breaking a big function in smaller pieces doesn't mean you need to redo your logic. If your teacher was happy with your first implementation, just keep it and isolate each part