Zooming in too far causes display to become blank

[brta-jc]

Hi all,
Thank you for any help in advance.

My team is having an issue with the GUI editor when we zoom. At one zoom level we have this:

Once we zoom in one more level / tick on the scroll wheel, the state machine representation / window goes blank. The rest of RAFCON is fine, like so:

2025-02-11 16:55:34:     INFO - rafcon.gui.controllers.graphical_editor_gaphas:  Opening the state machine caused some meta data to be generated, which will be stored  when the state machine is being saved.
2025-02-11 16:55:34:  VERBOSE - rafcon.gui.controllers.graphical_editor_gaphas:  Time spent in setup canvas 0.04892301559448242 state machine 1
2025-02-11 16:55:35:     INFO - rafcon.gui.controllers.main_window:  Ready

(ros2:5727): Pango-WARNING **: 16:55:42.960: failed to create cairo scaled font, expect ugly output. the offending font is 'Font Awesome 5 Free Heavy 59622.3349609375'

(ros2:5727): Pango-WARNING **: 16:55:42.960: font_face status is: error occurred in libfreetype

(ros2:5727): Pango-WARNING **: 16:55:42.960: scaled_font status is: error occurred in libfreetype
Traceback (most recent call last):
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/decorators.py", line 137, in async_wrapper
    func(*args, **kwargs)
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/view.py", line 796, in update_back_buffer
    self.painter.paint(Context(cairo=cr, items=items))
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/painter.py", line 74, in paint
    painter.paint(context)
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/painter.py", line 143, in paint
    self.draw_items(context.items, cairo)
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/painter.py", line 120, in draw_items
    self.draw_item(item, cairo)
  File "/home/ros/.local/lib/python3.10/site-packages/gaphas/painter.py", line 113, in draw_item
    cairo.restore()
cairo.Error: error occurred in libfreetype

(ros2:5727): Gtk-WARNING **: 16:55:42.961: drawing failure for widget 'GtkLabel': error occurred in libfreetype
(ros2:5727): Gtk-WARNING **: 16:55:42.961: drawing failure for widget 'GtkButton': error occurred in libfreetype
(ros2:5727): Gtk-WARNING **: 16:55:42.961: drawing failure for widget 'GtkBox': error occurred in libfreetype
(ros2:5727): Gtk-WARNING **: 16:55:42.961: drawing failure for widget 'GtkEventBox': error occurred in libfreetype
(ros2:5727): Gtk-WARNING **: 16:55:42.961: drawing failure for widget 'GtkNotebook': error occurred in libfreetype

When you zoom back out, the display recovers and is normal again. RAFCON continues to run fine, with no glitches other than the error log and visual element disappearing.
It looks like RAFCON is having trouble scaling the fonts? As above, the scale was 59622.3349609375, at a certain threshold it fails to scale and errors.

One thing to note:

• We're running on Ubuntu22 via WSL2, and most everything works great. We had some GTK issues causing the RAFCON GUI to crash using the default WSL2 window manager Wayland. The crash was a little bit similar, in that elements of the display were lost. However, in this case the entire program would eventually crash. Forcing WSL to use X11 (with VNC forwarding to windows) solved them, via export GDK_BACKEND=x11

Thanks again!

[JohannesErnst]

Hey @brta-jc,

thanks for posting the issue! First of all, nice to see that RAFCON generally runs in your Ubuntu22 environment and even in combination with Wayland. We are quite limited here in what environments we can test so it is good that other envs work as well (at least mostly).

I think I have noticed a similar bug on our setup as well in the past but it was very rarely and in combination with some very unusual zooming level. The problem is that it's kind of hard to reproduce this on our side and properly debug it further on. I will try to investigate a little bit more but cannot promise anything.

For further information, I think it would be nice to know what screen resolution you are running (we noticed at least some performance issues with 4k screens), how frequently this happens for you (also after reloading the state machine?) and if it persists if you zoom in even further. The latter would indicate that there is some kind of upper limit, how large the font can be scaled until it causes an error. Otherwise, it is the very specific font scale that creates the error.
When I zoom in a lot on my system I also get a Pango-CRITICAL, but the viewer does not show any issues, except that the font is not increasing resolution anymore:

Pango-CRITICAL **: 09:24:28.969: pango_font_description_set_size: assertion 'size >= 0' failed

If you want to investigate it more, I can at least for now suggest the following:

• The Font Awesome 5 Free Heavy is used by RAFCON to display the state names in the state editor. So I guess it makes sense that it causes your error when zooming, as the font needs to scale. You could try to replace the font in your installation with another one and see if the error persists. The fonts folder is in rafcon/share/fonts/type1.
• I am no expert in the topic, but I suspect that your custom setup with Wayland could also be the cause of the issue. Especially, since it was causing similar issues before. So I guess it is worth checking if the display servers settings (Wayland or with the env variable you have set X11) and font backend configurations are compatible. Maybe even some custom set environment variables like PANGO_FONT, GTK_FONT, or GDK_SCALE might be connected to the problem.
  I guess there is no option for you to test if the error reproduces in a native environment without the additional Wayland emulation layer?

I hope this helps at least a little bit, keep us updated!

[brta-hj]

Hi @JohannesErnst,

Thanks for the suggestions above. I have tried the font replacement (by pointing the ICON_FONT_AWESOME parameter in rafcon/gui/utils/constants.py to the "RAFCON" font).

This seems to have resolved the error about Font Awesome 5 Free Heavy 59622.3349609375, but now I get the error for the following font (which does not seem to be part of RAFCON fonts):

(ros2:20211): Pango-WARNING **: 11:30:26.683: failed to create cairo scaled font, expect ugly output. the offending font is 'DejaVu Sans 59622.3349609375'
(ros2:20211): Pango-WARNING **: 11:30:26.683: font_face status is: error occurred in libfreetype

(ros2:20211): Pango-WARNING **: 11:30:26.683: scaled_font status is: error occurred in libfreetype

(ros2:20211): Pango-WARNING **: 11:30:26.871: failed to create cairo scaled font, expect ugly output. the offending font is 'DejaVu Sans 73607.80859375'

(ros2:20211): Pango-WARNING **: 11:30:26.871: font_face status is: error occurred in libfreetype

(ros2:20211): Pango-WARNING **: 11:30:26.871: scaled_font status is: error occurred in libfreetype

As for the visual issue in the GUI, it remains. The state machine window still goes blank at that highly zoomed in level, and the terminal logs a lot of error occurred in libfreetype messages.

(I am also running in X11 mode on WSL2 as per @brta-jc message above)

[brta-hj]

I experience the same issue in the "99_bugs" included tutorial state machine, if that helps to reproduce on your end. Just zooming in a lot on any one of the internal blocks causes the errors to appear, this time the font called out is Source Sans Pro.

Once the initial error occurs, I get the following Gtk-WARNING errors indefinitely when changing the zoom or moving the view around:

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkLabel': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkBox': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkEventBox': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkNotebook': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkBox': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkPaned': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkBox': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkPaned': error occurred in libfreetype

(rafcon:17455): Gtk-WARNING **: 12:47:08.396: drawing failure for widget 'GtkPaned': error occurred in libfreetype

[JohannesErnst]

Hi @brta-hj,

okay, thanks for testing it. From that I conclude that it has nothing to do with the font directly. Although DejaVu Sans and Source Sans Pro don't appear in the RAFCON code directly, maybe they are still being used but selected via a different string.

I cannot reproduce the same behavior that you experience, even with the 99_bugs state machine. I don't think it is connected to the state machine specifically but rather generally to how data ports, connection lines and state names are scaled on high zooming levels.
Therefore, I at least investigated the Pango-CRITICAL error that gets thrown in my setup. Even though it doesn't lead to problems on my end, it might be the cause for the issue on your end when put in combination with the additional environment overhead you are using.
I spend some hours debugging the code and found that the layout = PangoCairo.create_layout(cairo_context) seems to be the culprit. I detected problematic usages in the following three files:

• RAFCON/source/rafcon/gui/mygaphas/items/state.py

  Line 502 in 99e0dab

  layout = PangoCairo.create_layout(cairo_context)

  
  

  RAFCON/source/rafcon/gui/mygaphas/items/state.py

  Lines 525 to 530 in 99e0dab

  	c.move_to(width / 2. - layout.get_size()[0] / float(SCALE) / 2.,
  	height / 2. - layout.get_size()[1] / float(SCALE) / 2.)
  	c.set_source_rgba(*gap_draw_helper.get_col_rgba(color, transparency))
  	PangoCairo.update_layout(cairo_context, layout)
  	PangoCairo.show_layout(cairo_context, layout)

• RAFCON/source/rafcon/gui/mygaphas/items/line.py

  Lines 263 to 267 in 99e0dab

  	layout = get_text_layout(cairo_context, self.name, FONT_SIZE)
  	ink_extents, logical_extents = layout.get_extents()
  	extents = [extent / float(SCALE) for extent in [logical_extents.x, logical_extents.y,
  	logical_extents.width, logical_extents.height]]

  
  

  RAFCON/source/rafcon/gui/mygaphas/items/line.py

  Line 285 in 99e0dab

  PangoCairo.show_layout(cairo_context, layout)

• RAFCON/source/rafcon/gui/mygaphas/utils/gap_draw_helper.py

  Lines 118 to 127 in 99e0dab

  	layout = PangoCairo.create_layout(cairo_context)
  	layout.set_text(text, -1)
  	font_name = constants.INTERFACE_FONT
  	font = FontDescription(font_name + " " + str(FONT_SIZE))
  	layout.set_font_description(font)
  	ink_extents, logical_extents = layout.get_extents()
  	extents = [extent / float(SCALE) for extent in [logical_extents.x, logical_extents.y,
  	logical_extents.width, logical_extents.height]]

  
  

  RAFCON/source/rafcon/gui/mygaphas/utils/gap_draw_helper.py

  Line 192 in 99e0dab

  PangoCairo.show_layout(cairo_context, layout)

Right now I cannot spend more time on this, feel free to investigate yourself. The lines above can serve as a reference on where to continue debugging. My suspicion is that the cairo_context that is passed in each case is somehow parameterized in a bad way causing problems when trying to e.g. layout.get_extents() or PangoCairo.show_layout(cairo_context, layout)

[brta-hj]

Hi @JohannesErnst,

Great, thanks for investigating it a bit further for us. I will have a look at the sections you mention above and try to debug further.

If possible, can you please share what your environment setup is like?

[brta-hj]

Just a small update: I've replaced all occurrences of font-family: 'Source Sans Pro' in the various css files in rafcon/share/themes folder with font-family: Monospace and that manages to get rid of the flood of Gtk-WARNING ** errors that were previously occuring after the initial scaled font error. Not really addressing the source of the problem here, but it does seem to have made the app more stable for me now.

As a sanity check, I have tried RAFCON in Ubuntu 20.04 on a VM I had and get only the Pango-CRITICAL error that you experience in your setup.

[JohannesErnst]

Hi @brta-hj,

good to know that you experience the same issue in a "normal" Linux environment without the additional Wayland layer. Currently, I am running on a openSUSE Leap 15.5 but without any virtual machine or WSL. I expect to test more on Ubuntu also in the future.

Interesting to know that the Source Sans Pro seems to be causing the Gtk-WARNING on your system. The error source is probably in the same direction.

As the original "blank display issue" does indeed seem to be connected to WSL2, maybe it is worth trying some different fonts or tweaking the env variables for this...