[swift]

HTTP2 supports server push, which should serve your needs for preloading just fine. (And there are other approaches as well; that's just one example.)

Browsers generally use the GPU for compositing web pages, but the CPU still generally does most of the rendering, and that frequently includes at least some of the image rendering. That's not actually relevant, though. The problem is bleeding; see here [1] for an example of someone encountering it in a gamedev context.

So how do you solve bleeding? If you read the answer to that Stack Overflow question, you'll see that it involves correctly setting up the data in the texture to avoid the issue. The problem is that browsers cannot assume that you've done that. The workaround depends on which graphics backend (OpenGL, D2D, etc.) is in use, but it can sometimes involve making a temporary copy of the region of the texture you're going to draw, which is obviously expensive.

As for server IO being slowed down by reading hundreds of small files from disk, I'd expect a properly configured server to be serving those files from memory, either explicitly or implicitly through the OS's filesystem cache.

[1] http://stackoverflow.com/questions/7894802/opengl-texture-at...