Drawing text with OpenGL seems to be interesting and portable possibility. After a little bit of trying i’ve got many different Unicode code points from different languages shown in OpenGL context:
mdzTextViewer is also available as 64-bit Windows 10 “S mode” package in Microsoft Store.
For macOS: XCode + SwiftUI/Cocoa + mdz_containers/mdz_editor libs looks promising.
For Linux: GTK + mdz_containers/mdz_editor libs seems to work. Code compiles and works just fine under Ubuntu 18.04 (showing main window, menu-bar, tabs-view, text-files under separate tabs) using GTK 2.0.
It works in both GNOME:
Weird is: under Ubuntu 14.04 the same code compiles and runs but shows only empty main window.
I decided not to touch Qt yet, because of commercial license limitations.
Also option of XLib + GLX looks interesting. Kind of “maximal portability” solution but without “native” look and fill.
mdzTextViewer is appeared. This Windows application allows viewing of text files with different Unicode encodings and converting/saving these files in different Unicode encodings.
Text convertions into different encodings are made using mdz_containers. The software is pretty fast (also with very large files), tiny and supports older platforms from Windows 2000.
The main engine of the program is a portable “mdz_editor” library which is yet has to be published. The library works under Android, macOS and Linux (Ubuntu) and i’d like to make port of viewer in one (or maybe a couple) of there OSes just for checking portability issues and demonstration.
At the moment UI part of Windows application is GDI-based. Maybe it worth to try OpenGL for UI code-portability on other platforms.