What’s even crazier is Apple wasn’t pleased with the difference in baseline filtering quality between the Intel HD 4000 and NVIDIA GeForce GT 650M GPUs. As the Retina Display MacBook Pro would have to regularly switch between GPUs, Apple wanted to ensure a consistently good experience regardless of which GPU was active. There are a lot of filtering operations at work when doing all of this resolution scaling, so rather than compromise user experience Apple simply wrote its own default filtering routines. Apple’s obsessive attention to detail really made it possible to pull all of this off. It’s just insane to think about.
To be quite honest, the hardware in the rMBP isn’t enough to deliver a consistently smooth experience across all applications. At 2880 x 1800 most interactions are smooth but things like zooming windows or scrolling on certain web pages is clearly sub-30fps. At the higher scaled resolutions, since the GPU has to render as much as 9.2MP, even UI performance can be sluggish. There’s simply nothing that can be done at this point - Apple is pushing the limits of the hardware we have available today, far beyond what any other OEM has done. Future iterations of the Retina Display MacBook Pro will have faster hardware with embedded DRAM that will help mitigate this problem. But there are other limitations: many elements of screen drawing are still done on the CPU, and as largely serial architectures their ability to scale performance with dramatically higher resolutions is limited.