Can't paint points on my widget

[mrjj]

@graniteDev

There should be a point at 100,200

insert qDebug() to be sure its called.

If you really dont want a custom widget for drawing, you can do like

QPixmap pix(200, 200);
pix.fill(Qt::blue);
QPainter painter(&pix);
painter.drawpoint(50, 50);
ui->label->setPixmap(pix); 

[graniteDev]

@mrjj WE HAVE A DOT!!!!!

UGH, I have no idea why the previous code did not work. But this looks like it does. I'm going to see if this works for me. I'm hoping that as it's updated with new data it does not flicker.

[mrjj]

@graniteDev
\o/
Long live the DOT.

Qwidgets uses double buffer system internally so often there is no flicker.

Did you use pixmap or paintEvent ?

[graniteDev]

@mrjj Crud, now I have a different problem, how do I draw different points with different sizes at the same time? Drawing many points of the same size is easy, that's readily handled, but I need to draw different sized points to denote how far or near a marker is that the point represents.

[graniteDev]

@mrjj said in Can't paint points on my widget:

@graniteDev
\o/
Long live the DOT.

Qwidgets uses double buffer system internally so often there is no flicker.

Did you use pixmap or paintEvent ?

void PointViewer::paintMarkers(int x, int y, int z)
{
    QPen pen(Qt::green, z, Qt::SolidLine, Qt::RoundCap);
    QPixmap pix(800,600);
    pix.fill(Qt::black);
    QPainter painter(&pix);
    painter.setPen(pen);
    painter.drawPoint(x,y);
    ui->pointViewerLabel->setPixmap(pix);
}

and I got a large green dot about where I expected to

[mrjj]

@graniteDev
Just include pointSize with the points.
like
struct PointData {
int x;
int y;
int z;
int DotSize
}

and give that to drawing routine.
And in paintEvent / for image, simply set penSize from data member
Its easy to handle as a struct as else u get many loose variables.

Since you clear the pixmap pr run.
pix.fill(Qt::black);
you need to draw all points each time. or keep pixmap as member in class and
draw on top each time.

where does the points come from ?

[graniteDev]

@mrjj There is a tracking camera that provides live x-y-z data. I'll have to apply a transform to make it fit in my viewing space...but that feels like the easy part right now, as I already have ready access to that data.

I don't quite follow what your saying, won't that only draw one dot at a time with the specified size? Then clear, and paint another dot of a different size, etc?

I'm using the z data to determine size, but the issue as I'm looking at the pen, is I can't assign a size to the point, because the size is applied to the pen, and the pen is applied to the painter, not the individual points that "drawPoints" draws.

[mrjj]

@graniteDev
maybe i didnt understand properly

Currently one x,y,z is painted. if you call
paintMarkers again, it will only show the last point.
If plan it to show many sets of x,y,z, you must handle that.
One options is to move pixmap to member and not clear it in
paintMarkers. that way you can draw over/keep the other points.
That is the goal correct ?
To draw many 3d points on same pixmap?
Alternatively, it should store the points and redraw all each time.

[graniteDev]

@mrjj Yes that is the goal, to have many points on a member variable pixMap that are all a unique size and position as determined by their x-y-z values.

[graniteDev]

@mrjj Interesting, so I added this code to my header file:

QPixmap m_pix;

This to my constructor:

PointViewer::PointViewer(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::PointViewer),
    m_pix(800,600)
{
    ui->setupUi(this);

    qDebug() << "test 11";

    m_pix.fill(Qt::black);
    ui->pointViewerLabel->setPixmap(m_pix);
}

And this to the paintMarkers function

void PointViewer::paintMarkers(int x, int y, int z)
{
    QPen pen(Qt::green, z, Qt::SolidLine, Qt::RoundCap);
    QPainter painter(&m_pix);
    painter.setPen(pen);
    painter.drawPoint(x,y);
    ui->pointViewerLabel->update();
}

and then called paintMarkers() with a button

void PointViewer::on_pushButton_clicked()
{
    paintMarkers(200, 300, 50);
}

and this did not work, so I'm not sure how to use a pixmap as a member variable and still get this to work. The pixmap did appear as a black 800x600 rectangle, so that part is working, but no green dot.

Thank you for you help btw!

[mrjj]

Hi
You are most welcome.
I think the error is
ui->pointViewerLabel->update();
as that would just make it draw the copy of pixmap it has.
you must call setPixmap again. (no need for update as that it will do it self)

[graniteDev]

oh...ok so
ui->pointViewerLabel->update() doesn't work, it needs to be ui->pointViewerLabel->setPixmap(m_pix);

[mrjj]

@graniteDev
Yes as update will just make it draw the COPY of the m_pix u give it in ctor.

[graniteDev]

@mrjj Ok that is working , but I can't get anymore than one dot to appear. How do I add points to draw with different pens? I tried this, just to see if it would work - ideally I'll need to iterate through a list of points in the future...

    QPen pen1(Qt::green, 50, Qt::SolidLine, Qt::RoundCap);
    QPen pen2(Qt::green, 10, Qt::SolidLine, Qt::RoundCap);
    QPainter painter(&m_pix);
    painter.setPen(pen1);
    painter.drawPoint(300,200);
    painter.setPen(pen2);
    painter.drawPoint(200,300);
    ui->pointViewerLabel->setPixmap(m_pix);

but I only got the first dot.

[mrjj]

@graniteDev
Well lets first test if
void PointViewer::on_pushButton_clicked()
{
paintMarkers(200, 300, 50);
paintMarkers(210, 300, 50);
paintMarkers(220, 300, 50);
}
does what we want. We could then add new paramter for size or color

[mrjj]

@graniteDev
Wont it be a green small dot in big green dot ?
try with red
QPen pen1(Qt::green, 50, Qt::SolidLine, Qt::RoundCap);
QPen pen2(Qt::red, 10, Qt::SolidLine, Qt::RoundCap);
QPainter painter(&m_pix);
painter.setPen(pen1);
painter.drawPoint(300,200);
painter.setPen(pen2);
painter.drawPoint(200,300);
ui->pointViewerLabel->setPixmap(m_pix);

[graniteDev]

@mrjj OH yes, I must have had the same exact point specified, as I tried that before and it didn't work, however this code yielded

void PointViewer::on_pushButton_clicked()
{
    paintMarkers(200, 300, 50);
    paintMarkers(250, 250, 40);
    paintMarkers(300, 200, 30);
}

[mrjj]

@graniteDev
Ok super.
So now i wondering if we could do

void PointViewer::on_pushButton_clicked()
{
paintMarkers(200, 300, 50, Qt::red , 32);
paintMarkers(250, 250, 40, Qt::blue,128 );
paintMarkers(300, 200, 30, QColor(255,0,0), 64);
}

so header/function be
void PointViewer::paintMarkers(int x, int y, int z, QColor dotColor, int dotSize)

would that be good enough ?
and u need to use them of course

void paintMarkers(int x, int y, int z, QColor dotColor, int dotSize)  {
QPen pen(dotColor, dotSize, Qt::SolidLine, Qt::RoundCap);
// could we use z to adjust dotSize?
QPainter painter(&m_pix);
painter.setPen(pen);
painter.drawPoint(x,y);
ui->pointViewerLabel->setPixmap(m_pix);

[graniteDev]

@mrjj Wow, ok this is working!! Thank you again so much for the help in understanding how to use these features.

I tried calling m_pix.fill(Qt::black); to clear m_pix to black again before painting new dots and this worked fine. However is this the most effective/efficient means of resetting m_pix before painting the new dots? I'll be dealing with live data at about ~50hz so I want to make this is as efficient as possible so that it looks live and fairly smooth to the user.

[mrjj]

@graniteDev
Well fill is pretty fast and setPixmap(m_pix) even if it makes copy should be pretty fast too due to implicit sharing. But the downside of using this image approach is that it will be slightly more heavy than a custom paint event. However, since the pixmap acts as a caches you get free speed
upgrade since you dont need to draw all points.
But say u make pixmap 1920x1080, this might be too heavy so also depends on image size.
( it takes time for QLabel to draw pixmap)
Also on small pc its far more heavy than say on big fat i7 desktop one.

so you might need a custom widget with paintEvent for optimal performance but depending on how many points and how big image must be, this might also work just fine even not the most
efficient way.