font size setting doesn't work in ddd(data display debugger)

I have fresh-installed Ubuntu 20.04 with GNOME lately, and installed ddd yesterday. The ddd font size is too small (12) so I changed the defaultFontSize value to 200 (from 120, in units of 1/10 points) in the preferences, but it doesn't have any effect. I also tried setting variableWidthFont which the manual says "is specified as an X font spec". It has no effect either.

This is the output when I start ddd:

Warning: Cannot convert string "-*-helvetica-medium-r-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
(Annoyed? Try 'Edit->Preferences->General->Suppress X Warnings'!)
Warning: Cannot convert string "-*-helvetica-medium-r-*-*-*-170-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-lucidatypewriter-medium-r-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-lucidatypewriter-bold-r-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-bold-r-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-medium-*-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-bold-*-*-*-*-200-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-helvetica-bold-r-*-*-*-300-*-*-*-*-iso8859-*" to type FontStruct
Warning: Cannot convert string "-*-symbol-*-*-*-*-*-200-*-*-*-*-adobe-*" to type FontStruct
Warning: Could not load font "-*-lucidatypewriter-medium-*-*-*-*-200-*-*-*-*-iso8859-*", using font "fixed" instead
Warning: Could not load font "-*-lucidatypewriter-medium-r-*-*-*-200-*-*-*-*-iso8859-*", using font "fixed" instead
Warning: Could not load font "-*-lucidatypewriter-bold-*-*-*-*-200-*-*-*-*-iso8859-*", using font "fixed" instead

Do I have to install any font package in Ubuntu 20.04 for this to work?

2 Answers

I found the warning when running ddd in ubuntu question in Stack Overflow and it gave me the solution. Run:

sudo apt-get install xfonts-100dpi

and logout and log back in. Then you can see that the font size changes.

I had the same problem on Ubuntu 20.04 (not just for ddd) and found that it is related to my new high-resolution monitor (3840x2160). As I do not need this high resolution for Ubuntu, I reduced it to 2560x1440 and everything is fine, including ddd.