Delay needed when loading a script

[willbelr]

A rendering problem affects 'graphics' terminal programs such as top and htop when they are launched using a script. A workaround consists in adding a short delay at the head of the script.

Expected Behavior

Correct rendering

Current Behavior

Incorrect rendering

Possible Solution

Not sure how it is handled in C++, but in PyQt sometimes this type of problem is caused by a premature function call somewhere, which can be delayed until next loop with QtCore.QTimer.singleShot(0, function)

Steps to Reproduce

Exemple code below. As shown, by adding sleep 0.1 && the problem is fixed.

#!/usr/bin/python3
import sys
from PyQt5 import QtWidgets
from QTermWidget import QTermWidget

with open("/tmp/test.sh", "w") as f:
    # f.write("sleep 0.1 && htop")  # good
    f.write("htop")  # bad


app = QtWidgets.QApplication(sys.argv)
term = QTermWidget(0)
term.setColorScheme("DarkPastels")
term.setShellProgram("/bin/bash")
term.setArgs(["/tmp/test.sh"])
term.startShellProgram()
term.show()
app.exec()

System Information

• Distribution & Version: Arch
• Kernel: 5.15.32-1-lts SMP Mon, 28 Mar 2022 08:54:31 +0000 x86_64 GNU/Linux
• Qt Version: 5.15.3
• lxqt-build-tools Version: 0.10.0-1
• Package version: 1.0.0-2

[yan12125]

There are other reports where sleep can workaround the issue. I cannot reproduce those issues reliably and I don't understand why it's broken, though. lxqt/qterminal#899, lxqt/qterminal#778

[tsujan]

this type of problem is caused by a premature function call somewhere

I wasn't able to reproduce the issue but, IMHO, this can be true. I've seen examples of it in Qt itself, although they weren't related to the current problem.

[willbelr]

Try launching the script from a desktop file. On my system, I can toggle the bug by setting terminal=true (good) or false (bad).

[Desktop Entry]
Exec=python /home/user/.local/share/scripts/primenote/primenote/__init__.py
Terminal=false

Also I noticed the bug happen when launching the script from xterm.desktop, but not urxvt.desktop. Sounds like it could stem from the environment, but I could not find a relevant variable yet. Might be somewhat related to #447

[willbelr]

I found the bug is caused by the LINES and COLUMNS environment variables, which are set by xterm (bad) but not rxvt (good). I use xterm to launch my scripts, hence the faulty variables of xterm were passed to QTermWidget. The problem is solved by unsetting those two before calling startShellProgram();

setEnvironment(["TERM=xterm", "LINES=", "COLUMNS="])

#!/usr/bin/python3
import sys
from PyQt5 import QtWidgets
from QTermWidget import QTermWidget

with open("/tmp/test.sh", "w") as f:
    # f.write("sleep 0.1 && htop")  # workaround 1
    # f.write("unset LINES && unset COLUMNS && htop")  # workaround 2
    f.write("htop")


app = QtWidgets.QApplication(sys.argv)
term = QTermWidget(0)
term.setColorScheme("DarkPastels")
term.setEnvironment(["TERM=xterm", "LINES=", "COLUMNS="])  # solution
term.setShellProgram("/bin/bash")
term.setArgs(["/tmp/test.sh"])
term.startShellProgram()
term.show()
app.exec()