ISF stands for Interactive Shader Format, it is an extension of the language GLSL that adds interactivity and dynamics. GLSL is a language created to interact directly with the gpu, commonly used to render images and videos based on complex mathematical formulas. ISF was created by the Company VidVox, which is an industry leader for creating live animations.
ISF adds that interactivity by letting you alter the variables that feed the formulas in real time.
ISF is very versatile in what it can do, from color correcting an existing photo or video to generating complex 3d fractals. Additionally, in your host program, you can chain ISF files together to create complex scenes that one file couldn’t do alone.
You don’t need to know how to program an ISF file to be able to use them effectively
ISF files are relatively lightweight, file sizes are usually less than 10kb, and it is essentially just a text file. When presenting visuals, you want to be able to run them as close to 60fps as possible, since ISF files are all mathematical formulas and GPUs are very good at calculating straight math, these files can run very fast.
ISF files can render images/videos that are very hard to replicate in 2d or 3d animation programs, particularly fractals. Some rendering engines such as Octane has experimental features for creating fractal meshes, however it still takes a screipt file that is very similar to openGL files
ISF files are dynamic. You can change the variables that feed the formula in real time. Your host program will be able to map values to those variables from stuff such as a knob on your controller or an audio frequency analysis
ISF files can loop seamlessly and indefinitly (or as long as your floats can be). Some files do break as they approach infinity, however this is more likely the formula breaking and not the framework.
ISF files can work on their own or input a photo or video
ISF files have a small but highly dedicated community with incrediably smart members
ISF files can do everything OpenGL can plus more.
You probably wouldn’t see an ISF file or openGL shader used in a high level production (Think Bonnaroo or Coachella). You are much more likely to find them in productions run by a smaller community, think Burning Man or small tier music/art festivals
Often these files are used as a visualizer for music or as part of a visualizer. A branch of this is Live Coding, where you write the file as it’s rendering.