A few years back, I was writting some technical blog post regarding Thai text rendering in games. Basically I was compaining that many game engine does not get it right. I created font-render-tester partly because I want screenshot to show what it should be, comparing to what many games render those Thai text.
This tool supports both TrueType-layout algorithm as well the OpenType shaping using Harfbuzz.
Glyphs are rendered by using FreeType 2 library. The UI is created using Dear ImGui.
Font Render Tester is available under MIT License.