I know that patent claims are typically much more specific than what the abstract suggests, and I only gave the claims a cursory read, but... surely there is prior art for this? I mean, I'm sure many non-web GUI systems avoid overdraw and at the very least, game rendering engines do, right? At least, I was under the illusion that overdraw was a big deal that at least shader-heavy renderers or old-school 80's/90's tile based renderers?