Layers All the Way Down: The Untold Story of Shader Compilation

Summary

Background As a game developer who works primarily in frameworks instead of engines, one of the biggest pain points is the need to render on multiple platforms efficiently. For most platform-level tasks, like window management, input handling, etc, SDL does a beautiful job and I barely have to think about it. Rendering, by comparison, is a huge can of worms. Every platform has their own unique support matrix. For Windows you have D3D12/D3D11/Vulkan/OpenGL. For Apple platforms you have Metal and OpenGL, or OpenGL ES if you’re on iOS/tvOS. For Linux and Nintendo you have Vulkan and OpenGL. For PlayStation you have whatever the hell they have going on over there. For Xbox you have D3D12 only. Android has Vulkan and OpenGL ES. You get the picture. All of these hardware acceleration APIs have similarities, but they have enough differences that mapping all the functionality you need onto them is nontrivial. I am a co-maintainer of the FNA project, which is a project that preserves the XNA framework on contemporary platforms. As part of this work for a few years I have worked on our cross-platform graphics abstraction FNA3D, particularly on the Vulkan implementation. This library allows us to translate XNA graphics calls to modern systems. My work on that project led me to create Refresh, which has a similar architecture but is influenced by the structure of Vulkan and modernized in several key regards. For the past several months I have been working on submitting a version of that API as a proposal to SDL. Ryan C. Gordon (aka icculus) announced plans to include a GPU API in SDL a few years ago. Refresh only differed from his proposal in a few small details, and the implementation was mostly complete, so the FNA team submitted what I had written in the hopes of saving some time and developer effort. For the most part this has been fairly well-received, but there is a question we have been asked repeatedly. Presently we support Vulkan, Metal, and D3D11, with other backends ...