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_, but needed when changing the grammar (glslang.y).
52 * [googletest][googletest]: _optional_, but should use if making any changes to glslang.
56 #### 1) Check-Out External Projects
59 cd <the directory glslang was cloned to, External will be a subdirectory>
60 git clone https://github.com/google/googletest.git External/googletest
65 Assume the source directory is `$SOURCE_DIR` and
66 the build directory is `$BUILD_DIR`:
68 For building on Linux (assuming using the Ninja generator):
73 cmake -GNinja -DCMAKE_BUILD_TYPE={Debug|Release|RelWithDebInfo} \
74 -DCMAKE_INSTALL_PREFIX=`pwd`/install $SOURCE_DIR
77 For building on Windows:
80 cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX=`pwd`/install
81 # The CMAKE_INSTALL_PREFIX part is for testing (explained later).
84 The CMake GUI also works for Windows (version 3.4.1 tested).
86 #### 3) Build and Install
93 cmake --build . --config {Release|Debug|MinSizeRel|RelWithDebInfo} \
97 If using MSVC, after running CMake to configure, use the
98 Configuration Manager to check the `INSTALL` project.
100 ### If you need to change the GLSL grammar
102 The grammar in `glslang/MachineIndependent/glslang.y` has to be recompiled with
103 bison if it changes, the output files are committed to the repo to avoid every
104 developer needing to have bison configured to compile the project when grammar
105 changes are quite infrequent. For windows you can get binaries from
106 [GnuWin32][bison-gnu-win32].
108 The command to rebuild is:
111 bison --defines=MachineIndependent/glslang_tab.cpp.h
112 -t MachineIndependent/glslang.y
113 -o MachineIndependent/glslang_tab.cpp
116 The above command is also available in the bash script at
117 `glslang/updateGrammar`.
122 Right now, there are two test harnesses existing in glslang: one is [Google
123 Test](gtests/), one is the [`runtests` script](Test/runtests). The former
124 runs unit tests and single-shader single-threaded integration tests, while
125 the latter runs multiple-shader linking tests and multi-threaded tests.
129 The [`runtests` script](Test/runtests) requires compiled binaries to be
130 installed into `$BUILD_DIR/install`. Please make sure you have supplied the
131 correct configuration to CMake (using `-DCMAKE_INSTALL_PREFIX`) when building;
132 otherwise, you may want to modify the path in the `runtests` script.
134 Running Google Test-backed tests:
143 ctest -C {Debug|Release|RelWithDebInfo|MinSizeRel}
145 # or, run the test binary directly
146 # (which gives more fine-grained control like filtering):
147 <dir-to-glslangtests-in-build-dir>/glslangtests
150 Running `runtests` script-backed tests:
153 cd $SOURCE_DIR/Test && ./runtests
156 ### Contributing tests
158 Test results should always be included with a pull request that modifies
161 If you are writing unit tests, please use the Google Test framework and
162 place the tests under the `gtests/` directory.
164 Integration tests are placed in the `Test/` directory. It contains test input
165 and a subdirectory `baseResults/` that contains the expected results of the
166 tests. Both the tests and `baseResults/` are under source-code control.
168 Google Test runs those integration tests by reading the test input, compiling
169 them, and then compare against the expected results in `baseResults/`. The
170 integration tests to run via Google Test is registered in various
171 `gtests/*.FromFile.cpp` source files. `glslangtests` provides a command-line
172 option `--update-mode`, which, if supplied, will overwrite the golden files
173 under the `baseResults/` directory with real output from that invocation.
174 For more information, please check `gtests/` directory's
175 [README](gtests/README.md).
177 For the `runtests` script, it will generate current results in the
178 `localResults/` directory and `diff` them against the `baseResults/`.
179 The integration tests to run via the `runtests` script is registered
180 via various `Test/test-*` text files and `Test/testlist`.
181 When you want to update the tracked test results, they need to be
182 copied from `localResults/` to `baseResults/`. This can be done by
183 the `bump` shell script.
185 The list of files tested comes from `testlist`, and lists input shaders
186 in this directory, which must all be public for this to work. However,
187 you can add your own private list of tests, not tracked here, by using
188 `localtestlist` to list non-tracked tests. This is automatically read
189 by `runtests` and included in the `diff` and `bump` process.
191 Programmatic Interfaces
192 -----------------------
194 Another piece of software can programmatically translate shaders to an AST
195 using one of two different interfaces:
196 * A new C++ class-oriented interface, or
197 * The original C functional interface
199 The `main()` in `StandAlone/StandAlone.cpp` shows examples using both styles.
201 ### C++ Class Interface (new, preferred)
203 This interface is in roughly the last 1/3 of `ShaderLang.h`. It is in the
204 glslang namespace and contains the following.
207 const char* GetEsslVersionString();
208 const char* GetGlslVersionString();
209 bool InitializeProcess();
210 void FinalizeProcess();
214 void setStrings(...);
215 const char* getInfoLog();
220 const char* getInfoLog();
224 See `ShaderLang.h` and the usage of it in `StandAlone/StandAlone.cpp` for more
227 ### C Functional Interface (orignal)
229 This interface is in roughly the first 2/3 of `ShaderLang.h`, and referred to
230 as the `Sh*()` interface, as all the entry points start `Sh`.
232 The `Sh*()` interface takes a "compiler" call-back object, which it calls after
233 building call back that is passed the AST and can then execute a backend on it.
235 The following is a simplified resulting run-time call stack:
238 ShCompile(shader, compiler) -> compiler(AST) -> <back end>
241 In practice, `ShCompile()` takes shader strings, default version, and
242 warning/error and other options for controlling compilation.
244 Basic Internal Operation
245 ------------------------
247 * Initial lexical analysis is done by the preprocessor in
248 `MachineIndependent/Preprocessor`, and then refined by a GLSL scanner
249 in `MachineIndependent/Scan.cpp`. There is currently no use of flex.
251 * Code is parsed using bison on `MachineIndependent/glslang.y` with the
252 aid of a symbol table and an AST. The symbol table is not passed on to
253 the back-end; the intermediate representation stands on its own.
254 The tree is built by the grammar productions, many of which are
255 offloaded into `ParseHelper.cpp`, and by `Intermediate.cpp`.
257 * The intermediate representation is very high-level, and represented
258 as an in-memory tree. This serves to lose no information from the
259 original program, and to have efficient transfer of the result from
260 parsing to the back-end. In the AST, constants are propogated and
261 folded, and a very small amount of dead code is eliminated.
263 To aid linking and reflection, the last top-level branch in the AST
264 lists all global symbols.
266 * The primary algorithm of the back-end compiler is to traverse the
267 tree (high-level intermediate representation), and create an internal
268 object code representation. There is an example of how to do this
269 in `MachineIndependent/intermOut.cpp`.
271 * Reduction of the tree to a linear byte-code style low-level intermediate
272 representation is likely a good way to generate fully optimized code.
274 * There is currently some dead old-style linker-type code still lying around.
276 * Memory pool: parsing uses types derived from C++ `std` types, using a
277 custom allocator that puts them in a memory pool. This makes allocation
278 of individual container/contents just few cycles and deallocation free.
279 This pool is popped after the AST is made and processed.
281 The use is simple: if you are going to call `new`, there are three cases:
283 - the object comes from the pool (its base class has the macro
284 `POOL_ALLOCATOR_NEW_DELETE` in it) and you do not have to call `delete`
286 - it is a `TString`, in which case call `NewPoolTString()`, which gets
287 it from the pool, and there is no corresponding `delete`
289 - the object does not come from the pool, and you have to do normal
290 C++ memory management of what you `new`
293 [cmake]: https://cmake.org/
294 [bison]: https://www.gnu.org/software/bison/
295 [googletest]: https://github.com/google/googletest
296 [bison-gnu-win32]: http://gnuwin32.sourceforge.net/packages/bison.htm