There's probably lots of room for optimization, for example currently it sets and resets all sorts of GPU state on each print call, for each character, which is rather expensive:

https://github.com/liamg/aminal/blob/master/glfont/font.go#L...

Speaking of the main loop, for every columm and every row:

    cx := uint(gui.terminal.GetLogicalCursorX())

which in turn calls another function -- move that outside of the loop and do it once. Generally buffer values that don't change and get used in loops, instead of fetching them by calling functions on each iteration.

Also, while it may not matter much in this case unless there are other sources of GC churn, just because I noticed it: don't create an array for the vertices for every character to then throw it away and recreate it, have one and keep reusing that.