We update the tool path with the cut path. So while it is not moving, per say, it HAS to be updated when running G code. I just loaded that 100MB file and looked at my GPU when it is running. The GPU does go up to about 25% (on one card only) with the tool path zoomed out. Zoomed in, 5% or less.
There are two options on how the tool path is run. Vertex Buffer Objects (aka VBOs, and requires OpenGL version >= 1.5) and the old Mach 3 way. We test for the v1.5 and if the driver supports it, we use VBOs. Typically, using VBOs puts more of the work on the GPU and less on the CPU. But usually, it also lends to smoother video as most graphics cards have faster memory that the RAM that the CPU uses. But... all graphics cards and their associated drivers are not created equally. Just because a drive reports that it can do OpenGL v1.5 doesn't mean it does it well. Some graphics cards may not even implement it in hardware but choose to emulate it in the driver software. We can't know this. All we can know is what the driver tells us. But finding out that some drivers just plain suck, we offered the option to disable the use of VBOs in the Mach config. This drops back to the old Mach 3 tool path code. The Mach 3 tool path style should use more CPU and less GPU. And it might now move around as slickly. I used to be able to tell the difference between the two methods, but with my current PC (4GHz 8 core), they feel about the same now.
BTW, as I was typing this, I loaded the 100MB file on my D2700MUD Atom board that uses an on-board cheap ass Intel GMA. It took like 15 minutes to load!!! (Atoms are so slow!) I have no way of looking at the GPU usage on it, but it does handle that file! I really didn't think it would. It seems to track ball around well.
Attached is the GPU graph while RUNNING the file with the tool path fully visible (zoomed out). The red peaks are ~25%.
Anyway, the only thing I can say is that you must have a driver or hardware issue that is causing the high GPU usage. What we do is relatively simple in comparison to something like a video game or even a 3D CAD program. My AutoDesk Inventor works my GPU much harder than the Mach 4 tool path does. All we have is a matrix of points that are connected by lines. This matrix gets dumped into video card memory (if using VBOs) or the computer RAM if not using VBOs. Nothing special. Once the matrix is loaded, we really don't do anything more with it except change bits and pieces of it "in memory". The rotation is handled purely by the OpenGL driver and video card. When more of the matrix is displayed in the view port, the more processing will be required. So seeing the GPU usage go up seems perfectly logical.
So what is causing the high GPU reading? Is it a driver or hardware issue (most likely) or maybe bad feedback to your GPU monitoring utility? That's about where we are at this point. Because if my Atom didn't choke on that 100MB file, I would expect most anything would run well if all was in working order.
Steve