How to paint to pixmap ?

[Dariusz]

Hey

I was trying to paint some icons/graphics to a pixmap for later usage but I either crash in python with no error or just fail.. how can I do this ?

class myPainter(QWidget):
    def __init__(self):
        super().__init__()
        self.iconList = {}
        self.l = QLabel("ascas")
        self.l.show()

    def drawIcons(self, val):
        if type(val) == list:
            for a in val:
                self.draw(a)
        else:
            print(val)
            self.draw(val)

    def draw(self, iconMode):
        m = QPixmap(500, 500)
        m.fill(Qt.yellow)
        p = QPainter(m)
        if iconMode == 0:
            p.setBrush(Qt.red)
            p.drawRect(QRect(0, 0, 100, 100))
            self.l.setPixmap(m)
            print("Drawing 0 ")

[mrjj]

Hi
It seems ok. ( as far as i can read python)
You create pixmap with some size. Assign the painter to it via its
ctor.

This surely paints

int GetBarHeight(int MAX) {
  return rand() % (MAX - 5) + 5;
}

void MainWindow::on_pushButton_released() {

  int h = ui->label->height();
  int w = ui->label->width();

  QPixmap pix(w, h);
  QPainter paint(&pix);
  pix.fill( Qt::white );
  paint.setPen(QColor(0, 0, 0, 255));


  int y = 0;
  int x = 0;

  int bw = 10; // bar width
  for (int barcount = 0; barcount < 12; ++barcount) {
    paint.setBrush(QColor(255 - x, 34 + x, 255, 255));
    paint.drawRect(x, h - GetBarHeight(h),  bw, h );
    x += bw + 4;
  }

  paint.end();
  ui->label->setPixmap(pix);
}

The crashing part is ODD. i though python was pretty safe int that reagrds.

In any case, you seem to assign it to a label ?

self.l.setPixmap(m)

Is the l valid ?
I assume you can have dangling pointers too in pyt.

[Dariusz]

@mrjj Thanks for example & checking it! I created label in constructor, will try ur code next, thanks!

[mrjj]

@Dariusz
Ok it was not dangling pointer then. :)
I tried for fun making invalid pixmap but i could make it crash.
Maximum effect was nothing shown.
So i have a feeling the crash might have been a bit unrelated to the pixmap.

But if this code also crashes, we might found some binding bug :)

[Dariusz]

@mrjj Running this code causes crash:

    def draw(self, iconMode):
        m = QPixmap(500,500)
       ...

Can't initialize QPixmap() with size.

If you could reproduce the crash, then we could post it to bug report :- )

[mrjj]

Hi
is
m = QPixmap(500,500)

like (c++)
QPixmap m(500,500);

or
QPixmap *m = new QPixmap (500,500);

Does it also crash there if you make new project and does nothing but
m = QPixmap(500,500)

If you can make a small example that crash, its ok to open bug report.

[Dariusz]

@mrjj I did some tests. I looks like it crashes when I do this p= QPainter(m), so passing it as source to QPainter o.O

[mrjj]

@Dariusz

Hi
well M seems to be a class member so
out of scope issues should not be possible.

So it could be a real bug if you can reproduce it in a minimal program.

[SGaist]

Hi,

Add p.end() when you're done painting. So in your code, before you call setPixmap.

[mrjj]

@SGaist
Good call.
It still works without painter.end();
in the c++ version but could be critical for a binding.

[SGaist]

I don't know how the binding manages that but when testing the code, I got the following message: QPaintDevice: Cannot destroy paint device that is being painted

[mrjj]

@SGaist
Ok that sounds a bit bad like -
"delete while in use" situation.
So it seems plausible it could crash from that in some cases.