1 Also see the Khronos landing page for glslang as a reference front end:
3 https://www.khronos.org/opengles/sdk/tools/Reference-Compiler/
5 The above page includes where to get binaries, and is kept up to date
6 regarding the feature level of glslang.
11 [![Build Status](https://travis-ci.org/KhronosGroup/glslang.svg?branch=master)](https://travis-ci.org/KhronosGroup/glslang)
13 An OpenGL and OpenGL ES shader front end and validator.
15 There are two components:
17 1. A front-end library for programmatic parsing of GLSL/ESSL into an AST.
19 2. A standalone wrapper, `glslangValidator`, that can be used as a shader
22 How to add a feature protected by a version/extension/stage/profile: See the
23 comment in `glslang/MachineIndependent/Versions.cpp`.
25 Things left to do: See `Todo.txt`
27 Execution of Standalone Wrapper
28 -------------------------------
30 To use the standalone binary form, execute `glslangValidator`, and it will print
31 a usage statement. Basic operation is to give it a file containing a shader,
32 and it will print out warnings/errors and optionally an AST.
34 The applied stage-specific rules are based on the file extension:
35 * `.vert` for a vertex shader
36 * `.tesc` for a tessellation control shader
37 * `.tese` for a tessellation evaluation shader
38 * `.geom` for a geometry shader
39 * `.frag` for a fragment shader
40 * `.comp` for a compute shader
42 There is also a non-shader extension
43 * `.conf` for a configuration file of limits, see usage statement for example
50 * [CMake][cmake]: for generating compilation targets.
51 * [bison][bison]: _optional_, for regenerating grammar (if changes).
55 1) Check out external projects:
58 git clone https://github.com/google/googletest.git External/googletest
61 2) Configure and build. Assume the source directory is `$SOURCE_DIR` and
62 the build directory is `$BUILD_DIR`:
65 # for building on Linux (assuming using the Ninja generator):
67 cmake -GNinja -DCMAKE_BUILD_TYPE={Debug|Release|RelWithDebInfo} \
68 -DCMAKE_INSTALL_PREFIX=`pwd`/install $SOURCE_DIR
71 # for building on Windows:
73 cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX=`pwd`/install
74 cmake --build . --config {Release|Debug|MinSizeRel|RelWithDebInfo}
76 # The CMAKE_INSTALL_PREFIX part is for testing (explained latter).
79 In MSVC, after running CMake, you may need to use the Configuration Manager to
80 check the INSTALL project.
82 ### If you need to change the GLSL grammar
84 The grammar in `glslang/MachineIndependent/glslang.y` has to be recompiled with
85 bison if it changes, the output files are committed to the repo to avoid every
86 developer needing to have bison configured to compile the project when grammar
87 changes are quite infrequent. For windows you can get binaries from
88 [GnuWin32][bison-gnu-win32].
90 The command to rebuild is:
93 bison --defines=MachineIndependent/glslang_tab.cpp.h
94 -t MachineIndependent/glslang.y
95 -o MachineIndependent/glslang_tab.cpp
98 The above command is also available in the bash script at
99 `glslang/updateGrammar`.
104 Right now, there are two test harnesses existing in glslang: one is [Google
105 Test](gtests/), one is the [`runtests` script](Test/runtests). The former
106 runs unit tests and single-shader single-threaded integration tests, while
107 the latter runs multiple-shader linking tests and multi-threaded tests.
111 The [`runtests` script](Test/runtests) requires compiled binaries to be
112 installed into `$BUILD_DIR/install`. Please make sure you have supplied the
113 correct configuration to CMake (using `-DCMAKE_INSTALL_PREFIX`) when building;
114 otherwise, you may want to modify the path in the `runtests` script.
116 Running Google Test-backed tests:
119 # assuming we are in the build directory:
121 # or, run the test binary directly
122 # (which gives more fine-grained control like filtering):
123 <dir-to-glslangtests-in-build-dir>/glslangtests
126 Running `runtests` script-backed tests:
129 # assuming we are in the source directory:
130 cd Test && ./runtests
133 ### Contributing tests
135 Test results should always be included with a pull request that modifies
138 If you are writing unit tests, please use the Google Test framework and
139 place the tests under the `gtests/` directory.
141 Integration tests are placed in the `Test/` directory. It contains test input
142 and a subdirectory `baseResults/` that contains the expected results of the
143 tests. Both the tests and `baseResults/` are under source-code control.
145 Google Test runs those integration tests by reading the test input, compiling
146 them, and then compare against the expected results in `baseResults/`. The
147 integration tests to run via Google Test is registered in various
148 `gtests/*.FromFile.cpp` source files. `glslangtests` provides a command-line
149 option `--update-mode`, which, if supplied, will overwrite the golden files
150 under the `baseResults/` directory with real output from that invocation.
151 For more information, please check `gtests/` directory's
152 [README](gtests/README.md).
154 For the `runtests` script, it will generate current results in the
155 `localResults/` directory and `diff` them against the `baseResults/`.
156 The integration tests to run via the `runtests` script is registered
157 via various `Test/test-*` text files and `Test/testlist`.
158 When you want to update the tracked test results, they need to be
159 copied from `localResults/` to `baseResults/`. This can be done by
160 the `bump` shell script.
162 The list of files tested comes from `testlist`, and lists input shaders
163 in this directory, which must all be public for this to work. However,
164 you can add your own private list of tests, not tracked here, by using
165 `localtestlist` to list non-tracked tests. This is automatically read
166 by `runtests` and included in the `diff` and `bump` process.
168 Programmatic Interfaces
169 -----------------------
171 Another piece of software can programmatically translate shaders to an AST
172 using one of two different interfaces:
173 * A new C++ class-oriented interface, or
174 * The original C functional interface
176 The `main()` in `StandAlone/StandAlone.cpp` shows examples using both styles.
178 ### C++ Class Interface (new, preferred)
180 This interface is in roughly the last 1/3 of `ShaderLang.h`. It is in the
181 glslang namespace and contains the following.
184 const char* GetEsslVersionString();
185 const char* GetGlslVersionString();
186 bool InitializeProcess();
187 void FinalizeProcess();
191 void setStrings(...);
192 const char* getInfoLog();
197 const char* getInfoLog();
201 See `ShaderLang.h` and the usage of it in `StandAlone/StandAlone.cpp` for more
204 ### C Functional Interface (orignal)
206 This interface is in roughly the first 2/3 of `ShaderLang.h`, and referred to
207 as the `Sh*()` interface, as all the entry points start `Sh`.
209 The `Sh*()` interface takes a "compiler" call-back object, which it calls after
210 building call back that is passed the AST and can then execute a backend on it.
212 The following is a simplified resulting run-time call stack:
215 ShCompile(shader, compiler) -> compiler(AST) -> <back end>
218 In practice, `ShCompile()` takes shader strings, default version, and
219 warning/error and other options for controlling compilation.
221 Basic Internal Operation
222 ------------------------
224 * Initial lexical analysis is done by the preprocessor in
225 `MachineIndependent/Preprocessor`, and then refined by a GLSL scanner
226 in `MachineIndependent/Scan.cpp`. There is currently no use of flex.
228 * Code is parsed using bison on `MachineIndependent/glslang.y` with the
229 aid of a symbol table and an AST. The symbol table is not passed on to
230 the back-end; the intermediate representation stands on its own.
231 The tree is built by the grammar productions, many of which are
232 offloaded into `ParseHelper.cpp`, and by `Intermediate.cpp`.
234 * The intermediate representation is very high-level, and represented
235 as an in-memory tree. This serves to lose no information from the
236 original program, and to have efficient transfer of the result from
237 parsing to the back-end. In the AST, constants are propogated and
238 folded, and a very small amount of dead code is eliminated.
240 To aid linking and reflection, the last top-level branch in the AST
241 lists all global symbols.
243 * The primary algorithm of the back-end compiler is to traverse the
244 tree (high-level intermediate representation), and create an internal
245 object code representation. There is an example of how to do this
246 in `MachineIndependent/intermOut.cpp`.
248 * Reduction of the tree to a linear byte-code style low-level intermediate
249 representation is likely a good way to generate fully optimized code.
251 * There is currently some dead old-style linker-type code still lying around.
253 * Memory pool: parsing uses types derived from C++ `std` types, using a
254 custom allocator that puts them in a memory pool. This makes allocation
255 of individual container/contents just few cycles and deallocation free.
256 This pool is popped after the AST is made and processed.
258 The use is simple: if you are going to call `new`, there are three cases:
260 - the object comes from the pool (its base class has the macro
261 `POOL_ALLOCATOR_NEW_DELETE` in it) and you do not have to call `delete`
263 - it is a `TString`, in which case call `NewPoolTString()`, which gets
264 it from the pool, and there is no corresponding `delete`
266 - the object does not come from the pool, and you have to do normal
267 C++ memory management of what you `new`
270 [cmake]: https://cmake.org/
271 [bison]: https://www.gnu.org/software/bison/
272 [googletest]: https://github.com/google/googletest
273 [bison-gnu-win32]: http://gnuwin32.sourceforge.net/packages/bison.htm