Fooling Around with Foveated Rendering
Shadertoy is a wonderful tool which lets users create and share a type of program called a fragment shader online. The true magic of shadertoy is its community of very talented graphics programmers who build incredible works of art despite having access to only a sliver of the traditional graphics pipeline.
Some of these shaders are very computationally intensive and even in a small window, they crawl along well below their intended 60 frames per second on my old laptop. Inspired by a technique in the VR community called Foveated Rendering, I decided to try to optimize these shaders by only rendering a fully detailed image within a small focal region. As you move away from the focal point the image quality decreases.
Source: Fooling Around with Foveated Rendering, an article by Peter Stefek.