I have a similar technique before, embedding the entire font data in the fragment shader source code. Then you can use `snprintf` to directly print into a GPU buffer mapped to the CPU (this is a footgun, I know). Instead of drawing individual characters with a vertex shader, I've just drawn one full screen triangle and use `gl_FragCoord` instead of UV coordinates. Not the most efficient way of doing things but it's a debug feature and it's fast enough to be practical.

Despite what the filename says, this is using the font from the IBM PC ROM, not the NES. You can find the "NES font" and other 8x8 pixel fonts around the web.

https://github.com/rikusalminen/triangles/blob/nesfont/shade...