This was the VGA standard. It was not built on a CRT controller; instead, the heart of the VGA chipset was a custom ASIC, a crystal, a bit of video RAM, and a digital to analog converter.
The result converts RGB and sync data for VGA into DIV-D. Since DVI-D and HDMI both use the same signals for video, this can be connected to either input on a monitor or TV. This implementation ...