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deshade

deshade is a library that allows you to dump and replace the shaders of any OpenGL or Vulkan application, which includes: GL2 + extensions, GL3, GL4, EGL, GLES2, GLES3, GLvnd, and Vulkan without recompiling the application for Linux.

Building

To build just run make

make

Running

By default, deshade will not dump an application shaders to disk to be replaced, unless a shaders directory exists where the application is invoked.

OpenGL

To dump and or replace the shaders of an OpenGL application, preload the deshade shared object with LD_PRELOAD like so:

mkdir shaders
LD_PRELOAD=./deshade.so application

Vulkan

To dump and or replace the shaders of a Vulkan application, the deshade.json and deshade.so need to be installed as an implicit layer with Vulkan inside ~/.local/share/vulkan/implicit_layer.d/ for the current user. Then enable the implicit layer with ENABLE_VK_LAYER_deshade=1 like so:

mkdir shaders
ENABLE_VK_LAYER_deshade=1 application

The shaders will be written to the shaders directory, their names will be the hash of their contents, with the following extension scheme: _vs.{glsl,bin} for vertex shaders, _fs.{glsl,bin} for fragment shaders, _gs.{glsl,bin} for geometry shaders, _cs.{glsl,bin} for compute shaders, _tcs.{glsl,bin} for tesselleation control shaders and _tes.{glsl,bin} for tesselation evaluation, and _ks.bin for Vulkan kernel shaders.

Replacing Shaders

Modifying the contents of one of the dumpped shaders in the shaders directory will take effect the next time the application is launched with deshade.

Debug Output

A debug log is also written to deshade.txt containing introspection information, if deshade fails to work check this for more information.

How it works

OpenGL

There are several ways OpenGL can be loaded.

• application dlopens libGL.so
• application dlopens libGLX_{vendor}.so, where vendor can be nvidia, intel, amd, mesa, etc
• application fetches OpenGL functions with glXGetProcAddress or glXGetProcAddressARB
• application links directly with -lGL
  • this loads functions through GLX
  • or, this loads functions through __glx_Main imports if using GLvnd

deshade attempts to supplement all of these so that regardless of how the application acquires an OpenGL context this should work.

Vulkan

Vulkan standardized a mechanism for doing these things called layers, deshade supplements some Vulkan functionality and and registers itself through the layer interface.

Known bugs

Applications which use multiple OpenGL contexts per thread may fail to work due to the way deshade only maintains one set of function pointers for the first context. Support for multiple contexts per thread would require supplementing the glXCreateContext, glXDestroyContext and glXMakeCurrent functions.

deshade exploits internal glibc dynamic linker functions to replace the dynamic linker itself to handle any applications that get OpenGL through dlopen, as a result this library is glibc specific and will not work on BSDs or musl based distributions.