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What is ISF?

ISF stands for "Interactive Shader Format", and is a file format that describes a GLSL fragment shader, as well as how to execute and interact with it. The goal of this file format is to provide a simple and minimal interface for image filters and generative video sources that allows them to be interacted with and reused in a generic and modular fashion. ISF is nothing more than a [slightly modified] GLSL fragment shader with a JSON blob at the beginning that describes how to interact with the shader (how many inputs/uniform variables it has, what their names are, what kind of inputs/variables they are, that sort of thing). ISF isn't some crazy new groundbreaking technology- it's just a simple and useful combination of two things that have been around for a while to make a minimal- but highly effective- filter format.

Downloads, sample files, and source code


Sample Files

Source Code

Spec Overview:

Functionally, you are limited only to what you can accomplish in a GLSL program (vertex + fragment shader, but the frag shader is where most of the action happens in most of the ISF files we've seen so far).

ISF's defining characteristic is the JSON dict at the beginning of your shader which describes it. This JSON dict contains the information describing how to interact with your shader- all the inputs, how many rendering passes there are and how to render them, etc. As a result of this, ISF is a very loose, open-ended file format: it can easily be extended by recognizing more keys in the future if we think of new things that might be nice to have.

How ISF works

When you load an ISF file, the shader code in your file is modified in memory during loading- some variables are declared, and some code is find-and-replaced. If you haven't explicitly created a vertex shader, one will automatically be generated. Each time you render a frame, the INPUTS variable values are passed to the shader, and then the shader is rendered (more than once if desired, potentially into image buffers accessible from different rendering passes and across different frames).

ISF-created variables

Additional Functions

<vec4> pixelColor = IMG_PIXEL(<image> imageName, <vec2> pixelCoord); <vec4> pixelColor = IMG_NORM_PIXEL(<image> imageName, <vec2> normalizedPixelCoord); <vec2> imageSize = IMG_SIZE(<image> imageName);

Multiple Rendering Passes, Rendering to Buffers

The ISF file format defines the ability to execute a shader multiple times in the process of rendering a frame for output- each time the shader's executed (each pass), the uniform int variable PASSINDEX is incremented. Details on how to accomplish this are described below in the spec, but the basic process involves adding an array of dicts to the PASSES key in your top-level JSON dict. Each dict in the PASSES array describes a different rendering pass- the ISF host will automatically create buffers to render into, and those buffers (and therefore the results of those rendering passes) can be accessed like any other buffer/input image/imported image (you can render to a texture in one pass, and then read that texture back in and render something else in another pass). The dicts in PASSES recognize a number of different keys to specify different properties of the rendering passes- more details are in the spec below.

Persistent Buffers

ISF files can define persistent buffers. These buffers are images (GL textures) that stay with the ISF file for as long as it exists. This is useful if you want to "build up" an image over time- you can repeatedly query and update the contents of persistent buffers by rendering into them- or if you want to perform calculations across the entire image, storing the results somewhere for later evaluation. Details on exactly how to do this are in the spec (below).

ISF Conventions

The ISF Specification vsn 2.0

First of all, there are super-simple examples that cover all of this- check out the various "Test____.fs" sample filters located here: ISF Test/Tutorial filters will probably learn more, faster, from the examples than you'll get by reading this document: each example describes a single aspect of the ISF file format, and they're extremely handy for testing, reference, or as a tutorial (the ISF file format is very small).

Converting Non-ISF GLSL shaders to ISF

Differences from the first version of the ISF spec

The first version of the ISF spec did some confusing and silly things that the second version improves on. If you want to write your own ISF host, and you want that host to support "old" ISF files, here's a link to the original ISF spec.

...and here's a list of the specific changes that were made from ISFVSN 1 to ISFVSN 2: