First, answered by Marc and codeling in this question, heightForWidth is only supported for QGraphicsLayout's subclasses.
Second, how to make a fixed aspect ratio window (or top-level widget) in qt (or pyqt) is a question that have been asked for years. However, as far as I know, there is no standard way of doing so, and it is something surprisingly hard to achieve. In short, my way of doing this is use Qt.FramelessWindowHint to create a frameless window without system move and resize function, and implement custom move and resize.
Explain important mechanism:
move:
- In
mousePressEvent, keep the place where we last clicked on the widget(the draggable area).
- In
mouseMoveEvent, calculate the distance between the last clicked point and the current mouse location. Move the window according to this distance.
resize:
- Find the increase or decrease step size of width and height by dividing the minimum width and height of the window by their highest common factor.
- Use the step size to increase or decrease the window size to keep the aspect ratio.
A screenshot to show that it can resize according to the aspect ratio.
The following code should works with both PyQt5 and Pyside2.
from PyQt5.QtCore import Qt, QRect, QPoint, QEvent
from PyQt5.QtWidgets import (QLabel, QMainWindow, QApplication, QSizePolicy,
QVBoxLayout, QWidget, QHBoxLayout, QPushButton)
from enum import Enum
class MainWindow(QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.setWindowFlags(Qt.FramelessWindowHint)
self.createCostumTitleBar()
self.setContentsMargins(0, 0, 0, 0)
self.central = QWidget()
self.central.setStyleSheet("background-color: #f8ecdf")
self.centralLayout = QVBoxLayout()
self.central.setLayout(self.centralLayout)
self.centralLayout.addWidget(
self.costumsystemmenu, alignment=Qt.AlignTop)
self.centralLayout.setContentsMargins(0, 0, 0, 0)
self.setCentralWidget(self.central)
# Set the minimum size to avoid window being resized too small.
self.setMinimumSize(300, 400)
self.minheight = self.minimumHeight()
self.minwidth = self.minimumWidth()
self.resize(300, 400)
# make sure your minium size have the same aspect ratio as the step.
self.stepY = 4
self.stepX = 3
# install the event filter on this window.
self.installEventFilter(self)
self.grabarea.installEventFilter(self)
self.cursorpos = CursorPos.DEFAULT
self.iswindowpress = False
def createCostumTitleBar(self):
self.costumsystemmenu = QWidget()
self.costumsystemmenu.setStyleSheet("background-color: #ccc")
self.costumsystemmenu.setContentsMargins(0, 0, 0, 0)
self.costumsystemmenu.setMinimumHeight(30)
self.grabarea = QLabel("")
self.grabarea.setStyleSheet("background-color: #ccc")
self.grabarea.setSizePolicy(
QSizePolicy.Expanding, QSizePolicy.Preferred)
titlebarlayout = QHBoxLayout()
titlebarlayout.setContentsMargins(11, 11, 11, 11)
titlebarlayout.setSpacing(0)
self.closeButton = QPushButton("X")
self.closeButton.setSizePolicy(
QSizePolicy.Minimum, QSizePolicy.Preferred)
self.closeButton.clicked.connect(self.close)
self.costumsystemmenu.setLayout(titlebarlayout)
titlebarlayout.addWidget(self.grabarea)
titlebarlayout.addWidget(self.closeButton, alignment=Qt.AlignRight)
self.istitlebarpress = False
def eventFilter(self, object, event):
# The eventFilter() function must return true if the event
# should be filtered, (i.e. stopped); otherwise it must return false.
# https://doc.qt.io/qt-5/qobject.html#eventFilter
# check if the object is the mainwindow.
if object == self:
if event.type() == QEvent.HoverMove:
if not self.iswindowpress:
self.setCursorShape(event)
return True
elif event.type() == QEvent.MouseButtonPress:
self.iswindowpress = True
# Get the position of the cursor and map to the global coordinate of the widget.
self.globalpos = self.mapToGlobal(event.pos())
self.origingeometry = self.geometry()
return True
elif event.type() == QEvent.MouseButtonRelease:
self.iswindowpress = False
return True
elif event.type() == QEvent.MouseMove:
if self.cursorpos != CursorPos.DEFAULT and self.iswindowpress:
self.resizing(self.globalpos, event,
self.origingeometry, self.cursorpos)
return True
else:
return False
elif object == self.grabarea:
if event.type() == QEvent.MouseButtonPress:
if event.button() == Qt.LeftButton and self.iswindowpress == False:
self.oldpos = event.globalPos()
self.oldwindowpos = self.pos()
self.istitlebarpress = True
return True
elif event.type() == QEvent.MouseButtonRelease:
self.istitlebarpress = False
return True
elif event.type() == QEvent.MouseMove:
if (self.istitlebarpress):
distance = event.globalPos()-self.oldpos
newwindowpos = self.oldwindowpos + distance
self.move(newwindowpos)
return True
else:
return False
else:
return False
# Change the cursor shape when the cursor is over different part of the window.
def setCursorShape(self, event, handlersize=11):
rect = self.rect()
topLeft = rect.topLeft()
topRight = rect.topRight()
bottomLeft = rect.bottomLeft()
bottomRight = rect.bottomRight()
# get the position of the cursor
pos = event.pos()
# make the resize handle include some space outside the window,
# can avoid user move too fast and loss the handle.
# top handle
if pos in QRect(QPoint(topLeft.x()+handlersize, topLeft.y()-2*handlersize),
QPoint(topRight.x()-handlersize, topRight.y()+handlersize)):
self.setCursor(Qt.SizeVerCursor)
self.cursorpos = CursorPos.TOP
# bottom handle
elif pos in QRect(QPoint(bottomLeft.x()+handlersize, bottomLeft.y()-handlersize),
QPoint(bottomRight.x()-handlersize, bottomRight.y()+2*handlersize)):
self.setCursor(Qt.SizeVerCursor)
self.cursorpos = CursorPos.BOTTOM
# right handle
elif pos in QRect(QPoint(topRight.x()-handlersize, topRight.y()+handlersize),
QPoint(bottomRight.x()+2*handlersize, bottomRight.y()-handlersize)):
self.setCursor(Qt.SizeHorCursor)
self.cursorpos = CursorPos.RIGHT
# left handle
elif pos in QRect(QPoint(topLeft.x()-2*handlersize, topLeft.y()+handlersize),
QPoint(bottomLeft.x()+handlersize, bottomLeft.y()-handlersize)):
self.setCursor(Qt.SizeHorCursor)
self.cursorpos = CursorPos.LEFT
# topRight handle
elif pos in QRect(QPoint(topRight.x()-handlersize, topRight.y()-2*handlersize),
QPoint(topRight.x()+2*handlersize, topRight.y()+handlersize)):
self.setCursor(Qt.SizeBDiagCursor)
self.cursorpos = CursorPos.TOPRIGHT
# topLeft handle
elif pos in QRect(QPoint(topLeft.x()-2*handlersize, topLeft.y()-2*handlersize),
QPoint(topLeft.x()+handlersize, topLeft.y()+handlersize)):
self.setCursor(Qt.SizeFDiagCursor)
self.cursorpos = CursorPos.TOPLEFT
# bottomRight handle
elif pos in QRect(QPoint(bottomRight.x()-handlersize, bottomRight.y()-handlersize),
QPoint(bottomRight.x()+2*handlersize, bottomRight.y()+2*handlersize)):
self.setCursor(Qt.SizeFDiagCursor)
self.cursorpos = CursorPos.BOTTOMRIGHT
# bottomLeft handle
elif pos in QRect(QPoint(bottomLeft.x()-2*handlersize, bottomLeft.y()-handlersize),
QPoint(bottomLeft.x()+handlersize, bottomLeft.y()+2*handlersize)):
self.setCursor(Qt.SizeBDiagCursor)
self.cursorpos = CursorPos.BOTTOMLEFT
# Default is the arrow cursor.
else:
self.setCursor(Qt.ArrowCursor)
self.cursorpos = CursorPos.DEFAULT
def resizing(self, originpos, event, geo, cursorpos):
newpos = self.mapToGlobal(event.pos())
# find the distance between new and old cursor position.
dist = newpos - originpos
# calculate the steps to grow or srink.
if cursorpos in [CursorPos.TOP, CursorPos.BOTTOM,
CursorPos.TOPRIGHT,
CursorPos.BOTTOMLEFT, CursorPos.BOTTOMRIGHT]:
steps = dist.y()//self.stepY
elif cursorpos in [CursorPos.LEFT, CursorPos.TOPLEFT, CursorPos.RIGHT]:
steps = dist.x()//self.stepX
# if the distance moved is too stort, grow or srink by 1 step.
if steps == 0:
steps = -1 if dist.y() < 0 or dist.x() < 0 else 1
oldwidth = geo.width()
oldheight = geo.height()
oldX = geo.x()
oldY = geo.y()
if cursorpos in [CursorPos.TOP, CursorPos.TOPRIGHT]:
width = oldwidth - steps * self.stepX
height = oldheight - steps * self.stepY
newX = oldX
newY = oldY + (steps * self.stepY)
# check if the new size is within the size limit.
if height >= self.minheight and width >= self.minwidth:
self.setGeometry(newX, newY, width, height)
elif cursorpos in [CursorPos.BOTTOM, CursorPos.RIGHT, CursorPos.BOTTOMRIGHT]:
width = oldwidth + steps * self.stepX
height = oldheight + steps * self.stepY
self.resize(width, height)
elif cursorpos in [CursorPos.LEFT, CursorPos.BOTTOMLEFT]:
width = oldwidth - steps * self.stepX
height = oldheight - steps * self.stepY
newX = oldX + steps * self.stepX
newY = oldY
# check if the new size is within the size limit.
if height >= self.minheight and width >= self.minwidth:
self.setGeometry(newX, newY, width, height)
elif cursorpos == CursorPos.TOPLEFT:
width = oldwidth - steps * self.stepX
height = oldheight - steps * self.stepY
newX = oldX + steps * self.stepX
newY = oldY + steps * self.stepY
# check if the new size is within the size limit.
if height >= self.minheight and width >= self.minwidth:
self.setGeometry(newX, newY, width, height)
else:
pass
# cursor position
class CursorPos(Enum):
TOP = 1
BOTTOM = 2
RIGHT = 3
LEFT = 4
TOPRIGHT = 5
TOPLEFT = 6
BOTTOMRIGHT = 7
BOTTOMLEFT = 8
DEFAULT = 9
if __name__ == "__main__":
import sys
app = QApplication(sys.argv)
w = MainWindow()
w.show()
sys.exit(app.exec_())
Finally, I'd like to give special thanks to the authors and editors of this question, GLHF, DRPK, Elad Joseph, and SimoN SavioR. Without their contribution to the community, it wouldn't be possible to come up with this answer.
