[SOLVED] PaintEvent, drawing many dots/points using Array.

[MrNoway]

Hey, I need little help with my script

so far I coded a dot, that moves from left to right.
HEADER
@class Lines : public QWidget
{
Q_OBJECT

QTimer *timer1;

public:
Lines(QWidget *parent = 0);
int timer_interval;

protected:
void paintEvent(QPaintEvent *event);
void drawLines(QPainter *qp);
public slots:
void call_repaint();

};@

MAIN
@Lines::Lines(QWidget *parent) : QWidget(parent)
{

timer_interval=0;
       timer1=new QTimer(this);
timer1->setInterval(100);
timer1->start();
connect(timer1, SIGNAL(timeout()), this, SLOT(call_repaint()));

}

void Lines::paintEvent(QPaintEvent *e)
{
Q_UNUSED(e);
QPainter qp(this);
drawLines(&qp);
}

void Lines::call_repaint(){repaint();}
void Lines::drawLines(QPainter *qp)
{
timer_interval++;

QPen pen(Qt::black, 2, Qt::SolidLine);
qp->setPen(pen);
qp->drawPoint(2+timer_interval,50);
}@

This is working fine, but I want instead one dot moving, many dots next to each other, so the dots are making a line or any kind of graph.

So long story short, I need an Array of the Paintevent or something, how to do this?

e.g.

first dot/point is on coordinate (10,10)
next one is on (10,11)
next one is on (10,12)
...

[giesbert]

Hi,

typically, the paint event repaints everything. It could also happen after the window was covered by another window. So if you really want to draw a line, move one end point and leave the starting point where it is.

If it should be dots, use an array.

[MrNoway]

@If it should be dots, use an array.@

-___-
yea, but how do I do this?

if I do like this, nothing is drawn

@ QPainter paint_array[10];

drawLines(&paint_array[0]);@

I want to draw a graph/curve, so I need to manipulate every single dot,
using a line is not an option for me

[terenty]

Hi! You dont have to create multiple QPainter objects or multiple painter events, you need to draw multiple dots using one painter inside one painter event, smthng like this:

@void Lines::drawLines(QPainter *qp)
{
timer_interval++;

QPen pen(Qt::black, 2, Qt::SolidLine);
qp->setPen(pen);
for(int i = 0; i < 50; i++){
qp->drawPoint(2+timer_interval,50+i);
}
}@

[giesbert]

Store the points in a member vector and use that for drawing:

@
class Lines : public QWidget
{
Q_OBJECT

QTimer *timer1;
QVector<QPoint> m_points;  // <<-- new

public:
Lines(QWidget *parent = 0);
int timer_interval;

protected:
void paintEvent(QPaintEvent *event);
void drawLines(QPainter *qp);
public slots:
void call_repaint();

};
@

in the cpp:

@
void Lines::call_repaint()
{
// <<-- new start
timer_interval++;
m_points.append(QPoint(2+timer_interval,50));
// <<-- new end
repaint();
}

void Lines::drawLines(QPainter *qp)
{
QPen pen(Qt::black, 2, Qt::SolidLine);
qp->setPen(pen);

// <<-- new start
QPoint pt;
foreach(pt, m_points)
{
    qp->drawPoint(pt);
}
// <<-- new end

}
@

[MrNoway]

Wow thanks Gerolf,

surprisingly, this is working as I want, though I dont really understand how you set it up.
if you have little time, you may want to explain this in few words.

@ QVector<QPoint> m_points; // << What did you do right here, never seen this <QPoint> before an variable @

and this one here
@ QPoint pt;
foreach(pt, m_points)
{
qp->drawPoint(pt);
}@

[MrNoway]

ok anyway, just marked it as solved.

thanks again

[giesbert]

Hi MrNoway,

You should have a look at the docs for these classes :-)

• QPoint is just what the name says, a point. x and y.
• A QVector<QPoint> is a dynamic array of QPoint objects
• foreach is a for each loop (shortcut for for(i = 0; i < vec.count(), ++i) {pt = vec[i]; ...)

These are helpers that Qt provides the users :-)