vispy
Cannot render vispy when switching from non-vispy widget
Sorry for the unclear issue title.
Note that this issue is only with PyQt6 or PySide6, and not present in PyQt5 or PySide2.
Here's the output of vispy.sys_info()
WARNING: pyqt5 already imported, cannot switch to pyqt6
WARNING: pyqt5 already imported, cannot switch to pyside2
WARNING: pyqt5 already imported, cannot switch to pyside6
Platform: Windows-10-10.0.19044-SP0
Python: 3.9.13 (tags/v3.9.13:6de2ca5, May 17 2022, 16:36:42) [MSC v.1929 64 bit (AMD64)]
NumPy: 1.23.3
Backend: PyQt5
pyqt4: None
pyqt5: ('PyQt5', '5.15.7', '5.15.2')
pyqt6: ('PyQt6', '6.3.1', '6.3.1')
pyside: None
pyside2: ('PySide2', '5.15.2.1', '5.15.2')
pyside6: ('PySide6', '6.3.1', '6.3.1')
pyglet: None
glfw: None
sdl2: None
wx: None
egl: None
osmesa: None
tkinter: None
jupyter_rfb: None
_test: None
GL version: '4.6.14800 Compatibility Profile Context 22.5.1 30.0.15021.11005'
MAX_TEXTURE_SIZE: 16384
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And here's a minimal viable example of what I'm trying to get to work.
from PyQt6.QtCore import QTimer, pyqtSignal
from PyQt6.QtWidgets import QApplication, QMainWindow, QVBoxLayout, QWidget, QPushButton
from vispy import scene
import numpy as np
import sys
N = 200
pos = np.zeros((N, 2), dtype=np.float32)
x_lim = [50., 750.]
y_lim = [-2., 2.]
pos[:, 0] = np.linspace(x_lim[0], x_lim[1], N)
pos[:, 1] = np.random.normal(size=N)
class ChildButtonVispyWidget(QWidget):
def __init__(self, set_vispy_widget_signal):
super().__init__()
button = QPushButton("Start Vispy!")
button.clicked.connect(set_vispy_widget_signal)
self.canvas = scene.SceneCanvas()
self.line = scene.Line(pos=pos)
self.line.parent = self.canvas.central_widget
layout = QVBoxLayout()
layout.addWidget(button)
layout.addWidget(self.canvas.native)
self.setLayout(layout)
self.timer = QTimer()
self.timer.setInterval(1000)
self.timer.timeout.connect(self.update)
self.timer.start()
def update(self):
global pos
pos[:, 1] = np.random.normal(size=N, scale=500)
self.line.set_data(pos)
class ChildVispyWidget(QWidget):
def __init__(self):
super().__init__()
self.canvas = scene.SceneCanvas()
self.line = scene.Line(pos=pos)
self.line.parent = self.canvas.central_widget
layout = QVBoxLayout()
layout.addWidget(self.canvas.native)
self.setLayout(layout)
self.timer = QTimer()
self.timer.setInterval(1000)
self.timer.timeout.connect(self.update)
self.timer.start()
def update(self):
global pos
pos[:, 1] = np.random.normal(size=N, scale=500)
self.line.set_data(pos)
class ChildButtonWidget(QWidget):
def __init__(self, set_vispy_widget_signal):
super(ChildButtonWidget, self).__init__()
button = QPushButton("Start Vispy!")
button.clicked.connect(set_vispy_widget_signal)
layout = QVBoxLayout()
layout.addWidget(button)
self.setLayout(layout)
class MainWindow(QMainWindow):
start_vispy = pyqtSignal()
def __init__(self):
super().__init__()
self.vispy_widget = None
print("MainWindow started")
self.setWindowTitle("Main window for vispy test")
self.start_vispy.connect(self.set_child_vispy_widget)
self.set_child_btn_widget()
#self.set_child_vispy_widget()
#self.set_child_vispy_btn_widget()
def set_child_btn_widget(self):
print("Setting child widget")
btn_widget = ChildButtonWidget(self.start_vispy)
self.setCentralWidget(btn_widget)
def set_child_vispy_widget(self):
print("Setting vispy widget")
vispy_widget = ChildVispyWidget()
self.setCentralWidget(vispy_widget)
def set_child_vispy_btn_widget(self):
print("Setting vispy + button widget")
vispy_btn_widget = ChildButtonVispyWidget(self.start_vispy)
self.setCentralWidget(vispy_btn_widget)
app = QApplication(sys.argv)
window = MainWindow()
window.show()
app.exec()
So, here's the issue:
When the central widget is switched from a widget which doesn't have a vispy widget in its layout, switching to a vispy widget fails with WARNING: void __cdecl QPlatformBackingStore::composeAndFlush(class QWindow *,const class QRegion &,const class QPoint &,class QPlatformTextureList *,bool) no opengl support set
However, this is not an issue when the child I'm trying switch to is set as the default child on PyQt/PySide startup, nor is it an issue when I switch from a child widget which already has a vispy child.
You can comment out one of self.set_child_vispy_widget() or self.set_child_vispy_btn_widget() at end of MainWindow's init to see what I'm talking about.
This issue persists with PySide6 as well, but as noted at the beginning, cannot replicate it on PyQt5 or PySide6. Be sure to replace pyqtSignal() with Signal() when you switch to PySide6 or PySide2, and app.exec() to app.exec_() when you switch to older versions.
So my gut reaction is that this is a bug in Qt6 and is something we (vispy maintainers) won't be able to fix. The code in the vispy backend for all supported Qt libraries is pretty similar and doesn't differ much between Qt5 and Qt6. From what I remember most of the differences between Qt5 and 6 are the name changes for things like keyboard modifier enums. That said...
You may have tried this or I missed it in your description, but what if you have a QWidget as your central widget and then the vispy and button widgets you're using now are just children of that widget. Does that change the results at all? I've never changed the central widget in a Qt application after initially setting it. Obviously you're able to do it sometimes so it isn't explicitly disallowed, but I'm curious if it might be an easy workaround.
Another thing, you pass the start_vispy signal to some of the sub-widgets. This seems error-prone or at the very least like a design that could be improved. I would think it would be better to have a signal on the individual sub-widgets that you connect to the necessary methods of the main window. Eh, it is probably fine, it just makes me feel weird.
Lastly, you pass start_vispy and then connect the button clicked signal to it. I didn't know you could connect a signal to another signal like that. Cool!
I might not be that well versed in Qt, but how would one accomplish what you're asking by this?
what if you have a QWidget as your central widget and then the vispy and button widgets you're using now are just children of that widget.
I feel like that's what is done when you comment out self.set_child_vispy_btn_widget(). I don't know of anyway of changing layouts (to accomplish 'moving to a new view' effect) the without changing the central widget to something that has a different layout. Is there a way of destroying current layout and adding a new layout?
I would think it would be better to have a signal on the individual sub-widgets that you connect to the necessary methods of the main window.
You mean using something like changing the line button.clicked.connect(self.set_child_vispy_widget) to button.clicked.connect(self.parent().set_child_vispy_widget ?
There seems to be a paradigm of writing Qt apps in Python that I'm missing. I would appreciate any pointers to different ways of laying out complex Qt screens in Python. Thanks in advance!
Lastly, you pass start_vispy and then connect the button clicked signal to it. I didn't know you could connect a signal to another signal like that. Cool!
And this is the hacky way I do this. If I use a signal more than once or have to share signals between widgets that are siblings so can't pass signals between each other, I add a signal to sub-classed QApplication as described here: https://stackoverflow.com/a/73073783
I think I'll answer some of this out of order...
There seems to be a paradigm of writing Qt apps in Python that I'm missing. I would appreciate any pointers to different ways of laying out complex Qt screens in Python. Thanks in advance!
I'm definitely not an expert, but I know when code has a "smell" that just doesn't seem right.
And this is the hacky way I do this. If I use a signal more than once or have to share signals between widgets that are siblings so can't pass signals between each other, I add a signal to sub-classed QApplication as described here: https://stackoverflow.com/a/73073783
Speaking of code smell, this idea seems like there should be a better way. But again, not an expert, and there are definitely types of Qt applications I have not made that may make more sense with this QApplication idea, but it seems odd.
I feel like that's what is done when you comment out self.set_child_vispy_btn_widget(). I don't know of anyway of changing layouts (to accomplish 'moving to a new view' effect) the without changing the central widget to something that has a different layout. Is there a way of destroying current layout and adding a new layout?
Maybe you're right, ChildButtonVispyWidget is doing that and to adapt it to what I was saying would be that you change the child-widgets of that ChildButtonVispyWidget instance rather than changing the central widget of the main window. I think you can "just" set a new layout similar to how you did when you originally created the widget. I've never done this myself as when I needed to change widgets in the past I would use something like a stacked or tabbed widget and switch between the widgets I wanted to look at. This StackOverflow answer discusses how you could easily set an old layout onto a temporary QWidget and have it destroyed:
https://stackoverflow.com/a/10439207/433202
The main idea though is:
self.central_widget = QtGui.QWidget()
self.central_widget.setLayout(self.some_layout)
self.setCentralWidget(self.central_widget)
and then later calling self.central_widget.setLayout again with a new layout.
Note that this whole idea of using an "intermediate" QWidget was just a guess and something I was hoping could be tested to see if it helps with the issue. But also, as you said, maybe you're already doing this with the ChildButtonVispyWidget and just need to adjust it a little.