I'm working with a fairly old (7-8 years) app that relies upon a fairly unmaintained OpenGL wrapper & an associated lib for adding text inside said wrapper (glium & glium_text). I'm currently trying to get the app working again before getting libs updated and/or rewriting it in more maintained tools. I'm struggling to do so however, and this issue can be reproduced using the examples from the glium_text repository.

Using cargo run (cargo run --example hello_world), the app/example works as expected and shows the intended text. However, upon using the --release flag (cargo run --example hello_world --release), the text no longer shows up at all. It disappears entirely, though the app/example does compile just fine and no errors are reported.

I haven't been able to find much in the way of information for why this could be, or how to go about debugging it (much less the actual underlying cause and solution). My understanding was that debug builds just contain debug information but this is a rather big divergence in actual behavior (in that the library as a whole doesn't work).

What do I do here? What are the steps for tracking down the reasons this could occur?