The open-source version of info-beamer has a an environment variable called INFOBEAMER_FULLSCALE which lets it ignore the actual screen aspect ratio when scaling the GL viewport. I just verified that the Pi version also supports this variable and when set does the correct thing.
Unfortunately there is no config option in Infobeamer Hosted that allows to set the variable. To try this i had to add the environment variable manually by adding it to
/service/info-beamer/run. This is of course no real solution since this change will be lost on the next upgrade.
Would it be possible to add a config option for this? Or is there any other way to set custom environment variables?