You asked for it, you got it – the Visualizer. Version 3.3 provides a view of the file being processed. It shows both the static image (in blue) and a live run-time image in green, indicating progress completed. The red dot is the last known reported position of the spindle bit.

Linux/Raspberry Pi users, clone it from github or Windows and Mac users can download here:

http://zapmaker.grblcontroller.s3-website-us-west-2.amazonaws.com/

Enjoy – and send me feedback!