[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 :-)