The first schematic editor I ever used displayed with Regis graphics [1] on a VT125 terminal. But it only used a small subset of Regis. One escape sequence would put the terminal in a mode that mapped the 8th-bit set bytes to a bunch of arc- and line-segment glyphs that were entirely sufficient to display a circuit schematic. (And the 8th-bit clear bytes retained their ASCII encodings for labels.)
Drawing with these characters was very similar to these ascii drawings: one byte gave you a piece of a line (or an arc), and you built a grid of them. The schematic editor took a simple here's-the-grid-coordinate-of-an-element representation of the schematic, adjusted the offsets of the glyphs of that element, and built-up the grid of bytes to send to the terminal.