Thanks Donnie. I made a new build that uses some different compiling options and a sort of in-between version of SDL that still has SVG loading capability as a sort of last resort before I pull out the big guns. I was hoping you could check it out, it's labeled v1.16a on the downloads section. I'm still not entirely sure what's going on here, other than it sounds like something is severely slowing everything down and not giving very much CPU to the main PixelCNC thread that's running, which is very strange.
Was the toolpath that slowed down rendering very complex? Or was it pretty simple? Did toolpaths of equal complexity cause a slowdown in previous versions? The toolpath visibility button sticking is also extremely strange, as it's constantly refreshing the cursor position (from SDL, so maybe that's the culprit) and doing a simple check to see whether or not the cursor is over each rectangle for each button/editbox/checkbox/menu item on the screen, where it hilights green if it is and otherwise defaults. That information isn't even stored in memory, it's re-generated each frame, so I'm at a bit of a loss other than it being SDL, which could be remedied by completely removing it from PixelCNC entirely and just going with the raw method. I haven't seen problems like this with SDL in the past, but that was also before SDL was as big and complex as it is now, so maybe the devs have become somewhat overburdened with keeping compatibility and reliability up to snuff.
Another thing I'm looking at right now is some better debugging systems I can build into PixelCNC to make it easier to track down and determine issues on end-users' machines without requiring them to get their hands dirty, we'll see what comes of that. Anyway, let me know how v1.16a works out when you get a chance, and thanks for taking the time helping me to figure these issues out.