Fixed size QGraphicsView and QGraphicsScene - python-3.x

Question

I have a QMdiSubWindow, that contains a QTabWidget which contains QGraphicsView inside a widget with a QHBoxLayout. The sub window is in an mdi area in my main window. My objective is to have a fixed size for QGraphicScene, depending upon the paper size i am using.
The view should then either conform to the same size as the scene, showing no scroll bars if this area can fit the total available mdi area, resizing the subwindow as well, or should resize to fill the available area resizing the sub window too, and should show scroll bars to navigate to the remaining space.
My current approach revolves around resizing the mdi subwindow first, then making a call to resize the current active widget in the window's QTabWidget.
This is all done as per musicamante's implementation.
The current widget chooses the min value between the parent(QStackedWidget)'s parent(QTabWidget)'s parent (QMdiSubWindow)'s rect (as it is resized first) and the dimensions of the QGraphicsScene which is updated when I set the dimensions.
-> Set QGraphicsScene dimensions from user input
-> Resize sub window
-> Resize QGraphicsView
I use the same logic, on my program, which fails to show scroll bars at all and the view expands to fit the QGraphicsScene despite being told to be the size of the sub window instead (sub window is of correct size), and the following example, where they do show as necessary but are clipped off partially.
from PyQt5 import QtWidgets, QtCore, QtGui
paperSizes = {
"A0": {
"72": [2384, 3370],
"96": [3179, 4494],
"150": [4967, 7022],
"300": [9933, 14043]
},
"A1": {
"72": [1684, 2384],
"96": [2245, 3179],
"150": [3508, 4967],
"300": [7016, 9933]
},
"A2": {
"72": [1191, 1684],
"96": [1587, 2245],
"150": [2480, 3508],
"300": [4960, 7016]
},
"A3": {
"72": [842, 1191],
"96": [1123, 1587],
"150": [1754, 2480],
"300": [3508, 4960]
},
"A4": {
"72": [595, 842],
"96": [794, 1123],
"150": [1240, 1754],
"300": [2480, 3508]
}
}
class canvas(QtWidgets.QWidget):
def __init__(self, parent=None, size= 'A4', ppi= '72'):
super(canvas, self).__init__(parent)
self._ppi = ppi
self._canvasSize = size
self.painter = QtWidgets.QGraphicsScene()
self.painter.setBackgroundBrush(QtGui.QBrush(QtCore.Qt.white))
self.view = QtWidgets.QGraphicsView(self.painter)
# self.view.setMinimumSize(595, 842)
self.layout = QtWidgets.QHBoxLayout(self)
self.layout.addWidget(self.view, stretch = 1, alignment= QtCore.Qt.AlignCenter)
self.setLayout(self.layout)
self.painter.setSceneRect(0, 0, *paperSizes[self.canvasSize][self.ppi])
def resizeView(self, w, h):
self.painter.setSceneRect(0, 0, w, h)
self.adjustView()
def adjustView(self):
self.view.setSceneRect(0, 0, self.painter.sceneRect().width() - self.view.frameWidth() * 2,
self.painter.sceneRect().height())
# give the view some time to adjust itself
QtWidgets.QApplication.processEvents()
width = self.painter.sceneRect().width() + self.view.frameWidth()*2
if self.view.verticalScrollBar().isVisible():
width += self.style().pixelMetric(QtWidgets.QStyle.PM_ScrollBarExtent)
height = self.painter.sceneRect().height() + self.view.frameWidth()*2
if self.view.verticalScrollBar().isVisible():
height += self.style().pixelMetric(QtWidgets.QStyle.PM_ScrollBarExtent)
self.view.setFixedWidth(min(self.parent().rect().width() - self.view.frameWidth()*2, width))
self.view.setFixedHeight(min(self.parent().rect().height()- self.view.frameWidth()*2, height))
def resizeEvent(self, event):
self.adjustView()
def setCanvasSize(self, size):
self.canvasSize = size
def setCanvasPPI(self, ppi):
self.ppi = ppi
#property
def canvasSize(self):
return self._canvasSize
#property
def ppi(self):
return self._ppi
#canvasSize.setter
def canvasSize(self, size):
self._canvasSize = size
if self.painter:
self.resizeView(*paperSizes[self.canvasSize][self.ppi])
#ppi.setter
def ppi(self, ppi):
self._ppi = ppi
if self.painter:
self.resizeView(*paperSizes[self.canvasSize][self.ppi])
#property
def dimensions(self):
#returns the dimension of the current scene
return self.painter.sceneRect().width(), self.painter.sceneRect().height()
class AppDemo(QtWidgets.QMainWindow):
def __init__(self):
super(AppDemo, self).__init__()
self.centralwidget = canvas(self)
width, height = paperSizes['A4']['72']
wsetter = min(1800, width - self.centralwidget.view.frameWidth()*2)
hsetter = min(900, height - self.centralwidget.view.frameWidth()*2)
self.setFixedSize(wsetter, hsetter)
self.centralwidget.resizeView(width, height)
self.setCentralWidget(self.centralwidget)
self.setContextMenuPolicy(QtCore.Qt.CustomContextMenu)
self.customContextMenuRequested.connect(self.resizer)
self.show()
def resizer(self, point):
width, height = paperSizes['A0']['300']
wsetter = min(1800, width - self.centralwidget.view.frameWidth()*2)
hsetter = min(900, height - self.centralwidget.view.frameWidth()*2)
self.setFixedSize(wsetter, hsetter)
self.centralWidget().resizeView(width, height)
def main():
import sys
app = QtWidgets.QApplication(sys.argv)
w = AppDemo()
w.setWindowTitle('AppDemo')
w.centralwidget.resizeView(*paperSizes['A0']['72'])
w.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()

Answer 1

If you are going to always keep the default transformation (no scaling), it could make sense to set the view sceneRect using the actual scene rect as a reference.
Note that, since the window could be resized, it's usually better to use a common function to do so, and call it also within the resizeEvent(). This also ensures that the view is resized if the vertical scroll bar becomes visible.
class canvas(QtWidgets.QWidget):
def __init__(self, parent=None, size= 'A4', ppi= '72'):
# ...
w, h = paperSizes[self.canvasSize][self.ppi]
self.painter.setSceneRect(0, 0, w, h)
# ensure that the scene is always aligned on the left, instead of being
# centered (the default)
self.view.setAlignment(QtCore.Qt.AlignLeft|QtCore.Qt.AlignTop)
# no need for this here
# self.view.setSceneRect(0, 0, w, h)
def resizeView(self, w, h):
self.painter.setSceneRect(0, 0, w, h)
self.adjustView()
def adjustView(self):
self.view.setSceneRect(0, 0, self.painter.sceneRect().width() - self.view.frameWidth() * 2,
self.painter.sceneRect().height())
# give the view some time to adjust itself
QtWidgets.QApplication.processEvents()
width = self.painter.sceneRect().width() + self.view.frameWidth() * 2
if self.view.verticalScrollBar().isVisible():
width += self.style().pixelMetric(QtWidgets.QStyle.PM_ScrollBarExtent)
self.view.setFixedWidth(width)
def resizeEvent(self, event):
self.adjustView()
Obviously, if you're sure that the view will always show the full width of the scene, you could also completely disable the horizontal scrollbar by setting its horizontalScrollBarPolicy to Qt.ScrollBarAlwaysOff.