"Given that, you might get better performance writing a software rasterizer that puts the whole image into a single rectangle and put that on a single div without 3d transforms."
Is it slow for you? It's totally smooth for me, rendering full screen on a big retina display. I not sure I can imagine there's any way you could write a software renderer in JS to do that.
I found it to be horribly slow and really weird in Firefox (sometimes see-through walls, z-sorting somehow flipping with barrels behind columns being drawn in front).
In Chrome, though, it's buttery-smooth with only small glitching.
Still, both are glitchy. I'm glad I went with THREE.js and not CSS 3D transforms for my latest 3D web project. THREE.js just works.
Is it slow for you? It's totally smooth for me, rendering full screen on a big retina display. I not sure I can imagine there's any way you could write a software renderer in JS to do that.