Here’s a demo. It draws a white rectangle, then draws red lines at all four corners. You’ll see that some of the white rectangle shows inside the red lines. It appears that the red does cover some of the white, but definitely not all the white.
-- Use this function to perform your initial setup
-- This function gets called once every frame
background(40, 40, 50)
If you set strokeWidth large, you can see that the white is drawn only inside the rectangle, not centered on the line (that’s probably good. perhaps there is a setting for that).
If you set strokeWidth to 1, I think there is still white inside the red, but at retina resolution with my old eyes, I’m not sure.
Anyway, the rectangle is clearly inside the lines. And, again … is this intended. It certainly could be.