I'm dynamically creating some complex polygon VML in internet explorer 8 using javascript to overlay shapes (parcels, streets, etc) over some "satellite" GIS images. I don't have any mousemove events registered on any part of the vml layer, nor the rest of the page, however when I move my mouse around over the drawn objects, my iexplore.exe cpu spikes to 50%.
I used the "profiler" function of the IE developer tools, and I see very few javascript calls being made in the background over a long period (30 seconds or so) of moving my mouse over the vml shapes, so I can only imagine the browser is doing some sort of internal (and extremely expensive) computation on the mouse position. On some other complex vml objects that I've seen around the web, I move my mouse over them, and they do not spike the cpu.
When I originally render the shapes with vml, the cpu jumps to 5% for iexplore.exe. When I move my mouse one pixel on top of the shapes, the cpu also jumps around 5%. I wonder if for some reason the underlying renderer is rendering the shapes over and over again every time the mouse moves.
Has anyone ever experienced this kind of cpu spike with mousemove behavior with VML added to the page?
Thanks! -Matt Mendick