I did indeed make some more progress. Here’s a screenshot of the gui background in action. Doesn’t do much yet, but it’s a start.
Update 6/4:
I wasn’t sure I was going to make a new post or just add to this existing one, as doubtless less people will see it, but as it’s visually not much different from the image above I’m putting it in here. What you see below is hours of work trying to get AGS to draw a line on the screen. Eventually I settled on a dynamic sprite and a gui that covers the whole screen, and thus draws a line from the center of the gui outward.
Update 6/5:
Having a problem here, that line isn’t drawing all the way to the cursor. Some weird thing with AGS but whatever I’ll get it fixed. Needed a decent place to put this so I could refer to it as long as I had this space.