Directory	What is in it
`ogl46/`	GLSL sources of the OpenGL 4.6 renderer
`ogl46bin/`	SPIR-V binaries of `ogl46/` (optional, made by `compile_spirv.py`)
`vk14/`	GLSL sources of the Vulkan 1.4 renderer
`vk14bin/`	SPIR-V binaries of `vk14/` (optional, made by `compile_spirv.py`)

The renderers load the binary of a shader first, when there is one and it was compiled from the sources that are there now (manifest.txt of the directory of the binaries lists the sources of each binary with their hashes). Otherwise the source is compiled: by the OpenGL driver for ogl46/, by glslang inside the simulator for vk14/ (with a cache of the results in the directory of the user). gfx.shaders.binaries no in eu07.ini makes them always use the sources. The sources are needed even with the binaries: the directives of the materials (#pragma texture, #pragma param) are read from them.

Compiling to SPIR-V

python shaders/compile_spirv.py

compiles every shader of ogl46/ (with the variant MODEL_DRAWS of the vertex and fragment shaders) and of vk14/ with glslc (Vulkan SDK, VULKAN_SDK, or --glslc <path>). A single file compiles the same way by hand:

glslc --target-env=opengl4.5 ogl46/mat_default.frag -o ogl46bin/mat_default.frag.spv
glslc --target-env=opengl4.5 -DMODEL_DRAWS=1 ogl46/vertex.vert -o ogl46bin/vertex.vert.MODEL_DRAWS.spv
glslc --target-env=vulkan1.4 vk14/imgui.frag -o vk14bin/imgui.frag.spv

A binary made by hand isn't in the manifest, so it is taken without being compared with its source. After a change of a source, compile the binaries again (or delete them): a binary older than its source is not used, and the log says so.

Writing shaders

Every stage file starts with #version 460 core and #define STAGE_VERTEX 1 (STAGE_FRAGMENT, STAGE_GEOMETRY, STAGE_COMPUTE); files included by others (.glsl) don't.
Includes: #include "file.glsl", relative to the directory of the file.
Every input and output between the stages has an explicit layout(location = N), every sampler, image and block an explicit binding, every loose uniform an explicit location: SPIR-V has no names to link by. The locations of the inputs and outputs of ogl46/ are one table for all the shaders (a name has the same location everywhere), see ogl46/common.glsl.
The settings of the game (SHADOWMAP_ENABLED, ENVMAP_ENABLED, MOTIONBLUR_ENABLED, POSTFX_ENABLED, EXTRAEFFECTS_ENABLED, OUTPUT_GAMMA) are const bool (specialization constants in the binaries, ogl46/settings.glsl): use them in if, not in #if.
The constants of the game (bindings, sizes) are written in ogl46/common.glsl and vk14/common.glsl for the binaries; the game puts its own values before the sources and checks at the start that the files have the same ones (the shader validator in ci_shadervalidator checks them too).

vk14

The shaders of vk14/ are those of ogl46/ made for the descriptor sets of the Vulkan renderer (rendering/vulkan14/vulkan14bindings.h), drawn with the same matrices and the same conventions as the OpenGL renderer (nothing is turned upside down but the picture shown in the window, present.frag).

A stage file includes common.glsl right after its stage define. The pipeline layout it is drawn with is picked by a define before that include: none for the passes of the scene, LAYOUT_POST for the post-processing (with quad.vert), LAYOUT_CLUSTER for the compute passes of the light clusters, LAYOUT_UI for the user interface.
The scene: set PASS_SET holds the blocks of the scene, of the draws (model_draws[], the one of a draw picked by the push constant pc.draw), of the instances and of the lights and clusters, and the shadow, environment and headlight maps; set MATERIAL_SET the textures of the material at MATERIAL_TEXTURE_FIRST + unit of their #pragma texture. The names of the model block (modelview, param, opacity ...) stand for the fields of the draw, as in the MODEL_DRAWS variant of ogl46/.
The push constants (pc, PUSH_CONSTANTS_SIZE bytes) carry the draw and the parameters of the special shaders in pc.data[]; each of those says at the top what it takes from them. In the post-processing param stands for pc.data.
The settings are specialization constants with the ids SPEC_* (vk14/settings.glsl).
The features of the later stages of the renderer (the shadows of the lamps and the headlights, the contact shadows, the weather and its fog, the sky ambient light, the prefiltered environment map, the automatic exposure, soft and gpu particles) aren't in vk14/ yet; the code paths are the ones ogl46/ takes with them off, the fog is an analytic one (vk14/apply_fog.glsl).