trueSKY uses effects for rendering. An effect is a collection of shaders - vertex shaders, pixel shaders and so on, along with information on how to combine them, how to set render state when they are used, and what inputs they take.
Platform-specific derived classes of Effectare created with RenderPlatform::CreateEffect, RenderPlatform::CreateEffect and RenderPlatform::CreateEffect, usually with an extensionless filename passed to the function.
The RenderPlatform first looks for a platform-specific shader source file by appending its platform shader file extension - .fx effect files for DirectX, .glfx files for GLSL etc. If this is not found, the cross-platform .sfx extension is appended.