Spyder crashes at startup after setting custom high DPI scaling at less than 1.0

What steps reproduce the problem?

1. Spyder 4.0 crashes at startup after setting custom high DPI scaling at value less than 1.0
2. In Tools>Preferences>General>Interface set “Custom High DPI Scaling” at 0.8
3. Confirmation window “Spyder needs to restart to change the following setting” fails to list the new setting to be changed: shows only a blank bullet as opposed to when setting automatic high DPI scaling, which correctly shows the settings being changed.
4. When I hit yes to restart Spyder for the new setting to take effect, there is a floating point violation cum core dump.

What is the expected output? What do you see instead?

When performing auto DPI scaling the resulting font size is way too small. Was playing around: scaling factors greater than one increase the default font size, less than one should make them smaller. Was looking for a scaling factor to better use the screen without it becoming illegible, used to do this in spyder 3.*

ERROR MESSAGE in terminal:

(quant) cygnus_x1@BM-SurfaceBook-2:~$ spyder [1:1:0100/000000.837530:ERROR:broker_posix.cc(41)] Invalid node channel message [1:1:0100/000000.837621:ERROR:broker_posix.cc(41)] Invalid node channel message Floating point exception (core dumped)

I am able to restart spyder after resetting (spyder --reset).

Versions

• Spyder version: Spyder 4.0.0
• Python version: Python 3.7.5 64-bit
• Qt version: Qt 5.9.6
• PyQt version: PyQt5 5.9.2
• Operating System name/version: Linux 5.1.15-surface-linux-surface Ubuntu 18.04 LTS running on a Windows SurfaceBook 2 using the Linux jakeday kernel (https://github.com/jakeday/linux-surface)

Dependencies

cloudpickle >=0.5.0          :  1.2.2 (OK)
pygments >=2.0               :  2.5.2 (OK)
qtconsole >=4.6.0            :  4.6.0 (OK)
nbconvert >=4.0              :  5.6.1 (OK)
sphinx >=0.6.6               :  2.3.0 (OK)
pylint >=0.25                :  2.4.4 (OK)
psutil >=0.3                 :  5.6.7 (OK)
qtawesome >=0.5.7            :  0.6.0 (OK)
qtpy >=1.5.0                 :  1.9.0 (OK)
pickleshare >=0.4            :  0.7.5 (OK)
zmq >=17                     :  18.1.0 (OK)
chardet >=2.0.0              :  3.0.4 (OK)
numpydoc >=0.6.0             :  0.9.1 (OK)
spyder_kernels >=1.8.1;<2.0.0:  1.8.1 (OK)
qdarkstyle >=2.7             :  2.7 (OK)
atomicwrites >=1.2.0         :  1.3.0 (OK)
diff_match_patch >=20181111  :  20181111 (OK)
intervaltree                 :  None (OK)
watchdog                     :  None (OK)
keyring                      :  None (OK)
pexpect >=4.4.0              :  4.7.0 (OK)
pympler                      :  None (OK)
sympy >=0.7.3                :  None (NOK)
cython >=0.21                :  0.29.14 (OK)
IPython >=4.0                :  7.10.2 (OK)
matplotlib >=2.0.0           :  3.1.1 (OK)
pandas >=0.13.1              :  0.25.3 (OK)
numpy >=1.7                  :  1.17.4 (OK)
scipy >=0.17.0               :  1.3.2 (OK)
pyls >=0.31.2;<0.32.0        :  0.31.2 (OK)
xdg >=0.26                   :  0.26 (OK)
rtree >=0.8.3                :  0.8.3 (OK)

[ccordoba12]

I can confirm this problem. It seems it’s not possible to set a factor less than 1.0 by design.

@dalthviz, please take care of this one by adding a validation to the scaling factor so when users try to set a factor lesser than 1.0, we show a message saying that that’s not possible and setting a value of 1.0 on it.

[dalthviz]

@Boris-Molina inside Spyder you can try to use the zoom in the Editor (Ctrl++ and Ctrl+-) and the fonts size config (Appearance > Fonts > Plain Text/Rich Text), although probably it could not be enough. Also, maybe the following link could be of some help (regarding fractional scaling in Ubuntu 18.04): https://askubuntu.com/q/1029436