Why is origin of drawing not top left corner ?

elpidiovaldez5

I am using PyQt5. I want to make a QMainWIndow with a central widget containing a horizontal row of buttons. Beneath the buttons I want a framed panel with a grid background. The lines of the grid are drawing in the frame, but the origin is offset. How can I get the grid to be relative to (0,0) in the coordinates of the frame ?

Below I have given the relevant bits of code. It produces the buttons and frame, but the vertical grid lines are in the lower right of the frame.

class MainWindow(QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        vbl = QVBoxLayout()
        hbl = QHBoxLayout()

        hbl.addWidget(QPushButton('Start'))
        hbl.addWidget(QPushButton('End'))

        vbl.addLayout(hbl)

        fl = QVBoxLayout()
        s = Simulation()
        v = s.display()
        fl.addWidget(v)

        frame = QFrame()
        frame.setFrameStyle(QFrame.Panel)
        frame.setLayout(fl)

        vbl.addWidget(frame)

        w = QWidget()
        w.setLayout(vbl)
        self.setCentralWidget(w)

        self.show()

class Simulation:

    def __init__(self):
        _width = 20
       _height = 20

class SimScene(QGraphicsScene):

    def __init__(self, sim, parent=None):
        QGraphicsScene.__init__(self, parent)
        self._sim = sim

    def drawBackground(self, painter, rect):
        grid = 10.0
        lines = []
        for x in range(self._sim._width):
            lines.append(QLineF(x * grid, 0, x * grid, grid * self._sim._height))

        painter.drawLines(lines);

SGaist

Hi,

Here you can find the full explanation about Qt's coordinate system.

elpidiovaldez5

I found the answer:-

I am only drawing the background of QGraphicsScene. I still have not put any graphics items in the scene, so the system has no idea what size it should be. I added a call to v.setSceneRect(0,0,200,200) to specify the size of the grid and everything works.

Pablo J. Rogina

@elpidiovaldez5 please don't forget to mark your post as solved. Thanks.