How to displayed Thai vowels and tones?

When i displayed vowels and tones in Thai , it doesn’t display properly tones . And sometimes can be displayed tones but not the vowels follows

are the tones and vowels made up of different characters? There is a limitation when the resulting glyph has to unicode representation

Complex languages where subsequent characters combine into a single glyph and where the resulting glyph has no individual Unicode representation (e.g., Devanagari), have limited support in LVGL.