Our application utilizes a variety of numeric only fonts to display measurement values (so each font only contains about a dozen characters) Discovered that fonts with a line_height > 255 aren’t being displayed. I believe the cause of this is the definition of line_height in the lv_font_t structure. Would it be possible to use a #define for the line_height to allow using larger fonts?
I think it would be possible, however, can I ask why you require a line height taller than 255 pixels? It seems a bit large to me. 
As I mentioned here a few months ago:
On my computer monitor (~27in with a resolution of 1920x1080) I can only display 4-5 lines of text with a 200px font size.
Thank you for your reply.
Our application displays measurements on an HMI device that is often viewed across the room. Some customers only monitor a single real-time value which we want to display as large as we can.
I’ve just added support to it in dev-7.0 branch.
You need to enable LV_FONT_FMT_TXT_LARGE in lv_conf.h.