Also see the Khronos landing page for glslang as a reference front end:
https://www.khronos.org/opengles/sdk/tools/Reference-Compiler/
The above page includes where to get binaries, and is kept up to date regarding the feature level of glslang.
An OpenGL and OpenGL ES shader front end and validator.
There are several components:
-
A GLSL/ESSL front-end for reference validation and translation of GLSL/ESSL into an AST.
-
An HLSL front-end for translation of a broad generic HLL into the AST.
-
A SPIR-V back end for translating the AST to SPIR-V.
-
A standalone wrapper,
glslangValidator
, that can be used as a command-line tool for the above.
How to add a feature protected by a version/extension/stage/profile: See the
comment in glslang/MachineIndependent/Versions.cpp
.
Tasks waiting to be done are documented as GitHub issues.
To use the standalone binary form, execute glslangValidator
, and it will print
a usage statement. Basic operation is to give it a file containing a shader,
and it will print out warnings/errors and optionally an AST.
The applied stage-specific rules are based on the file extension:
.vert
for a vertex shader.tesc
for a tessellation control shader.tese
for a tessellation evaluation shader.geom
for a geometry shader.frag
for a fragment shader.comp
for a compute shader
There is also a non-shader extension
.conf
for a configuration file of limits, see usage statement for example
- CMake: for generating compilation targets.
- bison: optional, but needed when changing the grammar (glslang.y).
- googletest: optional, but should use if making any changes to glslang.
cd <parent of where you want glslang to be>
git clone [email protected]:KhronosGroup/glslang.git
cd <the directory glslang was cloned to, "External" will be a subdirectory>
git clone https://github.com/google/googletest.git External/googletest
Assume the source directory is $SOURCE_DIR
and
the build directory is $BUILD_DIR
:
For building on Linux (assuming using the Ninja generator):
cd $BUILD_DIR
cmake -GNinja -DCMAKE_BUILD_TYPE={Debug|Release|RelWithDebInfo} \
-DCMAKE_INSTALL_PREFIX=`pwd`/install $SOURCE_DIR
For building on Windows:
cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX=`pwd`/install
# The CMAKE_INSTALL_PREFIX part is for testing (explained later).
The CMake GUI also works for Windows (version 3.4.1 tested).
# for Linux:
ninja install
# for Windows:
cmake --build . --config {Release|Debug|MinSizeRel|RelWithDebInfo} \
--target install
If using MSVC, after running CMake to configure, use the
Configuration Manager to check the INSTALL
project.
The grammar in glslang/MachineIndependent/glslang.y
has to be recompiled with
bison if it changes, the output files are committed to the repo to avoid every
developer needing to have bison configured to compile the project when grammar
changes are quite infrequent. For windows you can get binaries from
GnuWin32.
The command to rebuild is:
bison --defines=MachineIndependent/glslang_tab.cpp.h
-t MachineIndependent/glslang.y
-o MachineIndependent/glslang_tab.cpp
The above command is also available in the bash script at
glslang/updateGrammar
.
Right now, there are two test harnesses existing in glslang: one is Google
Test, one is the runtests
script. The former
runs unit tests and single-shader single-threaded integration tests, while
the latter runs multiple-shader linking tests and multi-threaded tests.
The runtests
script requires compiled binaries to be
installed into $BUILD_DIR/install
. Please make sure you have supplied the
correct configuration to CMake (using -DCMAKE_INSTALL_PREFIX
) when building;
otherwise, you may want to modify the path in the runtests
script.
Running Google Test-backed tests:
cd $BUILD_DIR
# for Linux:
ctest
# for Windows:
ctest -C {Debug|Release|RelWithDebInfo|MinSizeRel}
# or, run the test binary directly
# (which gives more fine-grained control like filtering):
<dir-to-glslangtests-in-build-dir>/glslangtests
Running runtests
script-backed tests:
cd $SOURCE_DIR/Test && ./runtests
Test results should always be included with a pull request that modifies functionality.
If you are writing unit tests, please use the Google Test framework and
place the tests under the gtests/
directory.
Integration tests are placed in the Test/
directory. It contains test input
and a subdirectory baseResults/
that contains the expected results of the
tests. Both the tests and baseResults/
are under source-code control.
Google Test runs those integration tests by reading the test input, compiling
them, and then compare against the expected results in baseResults/
. The
integration tests to run via Google Test is registered in various
gtests/*.FromFile.cpp
source files. glslangtests
provides a command-line
option --update-mode
, which, if supplied, will overwrite the golden files
under the baseResults/
directory with real output from that invocation.
For more information, please check gtests/
directory's
README.
For the runtests
script, it will generate current results in the
localResults/
directory and diff
them against the baseResults/
.
When you want to update the tracked test results, they need to be
copied from localResults/
to baseResults/
. This can be done by
the bump
shell script.
You can add your own private list of tests, not tracked publicly, by using
localtestlist
to list non-tracked tests. This is automatically read
by runtests
and included in the diff
and bump
process.
Another piece of software can programmatically translate shaders to an AST using one of two different interfaces:
- A new C++ class-oriented interface, or
- The original C functional interface
The main()
in StandAlone/StandAlone.cpp
shows examples using both styles.
This interface is in roughly the last 1/3 of ShaderLang.h
. It is in the
glslang namespace and contains the following.
const char* GetEsslVersionString();
const char* GetGlslVersionString();
bool InitializeProcess();
void FinalizeProcess();
class TShader
bool parse(...);
void setStrings(...);
const char* getInfoLog();
class TProgram
void addShader(...);
bool link(...);
const char* getInfoLog();
Reflection queries
See ShaderLang.h
and the usage of it in StandAlone/StandAlone.cpp
for more
details.
This interface is in roughly the first 2/3 of ShaderLang.h
, and referred to
as the Sh*()
interface, as all the entry points start Sh
.
The Sh*()
interface takes a "compiler" call-back object, which it calls after
building call back that is passed the AST and can then execute a backend on it.
The following is a simplified resulting run-time call stack:
ShCompile(shader, compiler) -> compiler(AST) -> <back end>
In practice, ShCompile()
takes shader strings, default version, and
warning/error and other options for controlling compilation.
-
Initial lexical analysis is done by the preprocessor in
MachineIndependent/Preprocessor
, and then refined by a GLSL scanner inMachineIndependent/Scan.cpp
. There is currently no use of flex. -
Code is parsed using bison on
MachineIndependent/glslang.y
with the aid of a symbol table and an AST. The symbol table is not passed on to the back-end; the intermediate representation stands on its own. The tree is built by the grammar productions, many of which are offloaded intoParseHelper.cpp
, and byIntermediate.cpp
. -
The intermediate representation is very high-level, and represented as an in-memory tree. This serves to lose no information from the original program, and to have efficient transfer of the result from parsing to the back-end. In the AST, constants are propogated and folded, and a very small amount of dead code is eliminated.
To aid linking and reflection, the last top-level branch in the AST lists all global symbols.
-
The primary algorithm of the back-end compiler is to traverse the tree (high-level intermediate representation), and create an internal object code representation. There is an example of how to do this in
MachineIndependent/intermOut.cpp
. -
Reduction of the tree to a linear byte-code style low-level intermediate representation is likely a good way to generate fully optimized code.
-
There is currently some dead old-style linker-type code still lying around.
-
Memory pool: parsing uses types derived from C++
std
types, using a custom allocator that puts them in a memory pool. This makes allocation of individual container/contents just few cycles and deallocation free. This pool is popped after the AST is made and processed.The use is simple: if you are going to call
new
, there are three cases:-
the object comes from the pool (its base class has the macro
POOL_ALLOCATOR_NEW_DELETE
in it) and you do not have to calldelete
-
it is a
TString
, in which case callNewPoolTString()
, which gets it from the pool, and there is no correspondingdelete
-
the object does not come from the pool, and you have to do normal C++ memory management of what you
new
-