This repository contains GLSL source code for Perlin noise in 2D, 3D and 4D, both the modern simplex versions and the classic versions, including periodic noise similar to the pnoise() function in RenderMan SL. The functions have very good performance and no dependencies on external data. The code is open source, licensed under the terms of the OSI-approved and very permissive MIT license. For licensing details, please refer to the LICENSE file in the repository.