294 lines
9.9 KiB
Markdown
294 lines
9.9 KiB
Markdown
Also see the Khronos landing page for glslang as a reference front end:
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https://www.khronos.org/opengles/sdk/tools/Reference-Compiler/
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The above page includes where to get binaries, and is kept up to date
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regarding the feature level of glslang.
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glslang
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=======
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[](https://travis-ci.org/KhronosGroup/glslang)
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[](https://ci.appveyor.com/project/Khronoswebmaster/glslang/branch/master)
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An OpenGL and OpenGL ES shader front end and validator.
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There are two components:
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1. A front-end library for programmatic parsing of GLSL/ESSL into an AST.
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2. A standalone wrapper, `glslangValidator`, that can be used as a shader
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validation tool.
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How to add a feature protected by a version/extension/stage/profile: See the
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comment in `glslang/MachineIndependent/Versions.cpp`.
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Tasks waiting to be done are documented as GitHub issues.
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Execution of Standalone Wrapper
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-------------------------------
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To use the standalone binary form, execute `glslangValidator`, and it will print
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a usage statement. Basic operation is to give it a file containing a shader,
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and it will print out warnings/errors and optionally an AST.
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The applied stage-specific rules are based on the file extension:
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* `.vert` for a vertex shader
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* `.tesc` for a tessellation control shader
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* `.tese` for a tessellation evaluation shader
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* `.geom` for a geometry shader
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* `.frag` for a fragment shader
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* `.comp` for a compute shader
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There is also a non-shader extension
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* `.conf` for a configuration file of limits, see usage statement for example
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Building
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--------
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### Dependencies
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* [CMake][cmake]: for generating compilation targets.
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* [bison][bison]: _optional_, but needed when changing the grammar (glslang.y).
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* [googletest][googletest]: _optional_, but should use if making any changes to glslang.
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### Build steps
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#### 1) Check-Out External Projects
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```bash
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cd <the directory glslang was cloned to, External will be a subdirectory>
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git clone https://github.com/google/googletest.git External/googletest
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```
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#### 2) Configure
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Assume the source directory is `$SOURCE_DIR` and
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the build directory is `$BUILD_DIR`:
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For building on Linux (assuming using the Ninja generator):
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```bash
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cd $BUILD_DIR
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cmake -GNinja -DCMAKE_BUILD_TYPE={Debug|Release|RelWithDebInfo} \
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-DCMAKE_INSTALL_PREFIX=`pwd`/install $SOURCE_DIR
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```
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For building on Windows:
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```bash
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cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX=`pwd`/install
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# The CMAKE_INSTALL_PREFIX part is for testing (explained later).
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```
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The CMake GUI also works for Windows (version 3.4.1 tested).
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#### 3) Build and Install
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```bash
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# for Linux:
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ninja install
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# for Windows:
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cmake --build . --config {Release|Debug|MinSizeRel|RelWithDebInfo} \
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--target install
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```
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If using MSVC, after running CMake to configure, use the
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Configuration Manager to check the `INSTALL` project.
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### If you need to change the GLSL grammar
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The grammar in `glslang/MachineIndependent/glslang.y` has to be recompiled with
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bison if it changes, the output files are committed to the repo to avoid every
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developer needing to have bison configured to compile the project when grammar
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changes are quite infrequent. For windows you can get binaries from
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[GnuWin32][bison-gnu-win32].
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The command to rebuild is:
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```bash
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bison --defines=MachineIndependent/glslang_tab.cpp.h
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-t MachineIndependent/glslang.y
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-o MachineIndependent/glslang_tab.cpp
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```
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The above command is also available in the bash script at
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`glslang/updateGrammar`.
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Testing
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-------
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Right now, there are two test harnesses existing in glslang: one is [Google
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Test](gtests/), one is the [`runtests` script](Test/runtests). The former
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runs unit tests and single-shader single-threaded integration tests, while
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the latter runs multiple-shader linking tests and multi-threaded tests.
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### Running tests
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The [`runtests` script](Test/runtests) requires compiled binaries to be
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installed into `$BUILD_DIR/install`. Please make sure you have supplied the
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correct configuration to CMake (using `-DCMAKE_INSTALL_PREFIX`) when building;
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otherwise, you may want to modify the path in the `runtests` script.
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Running Google Test-backed tests:
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```bash
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cd $BUILD_DIR
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# for Linux:
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ctest
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# for Windows:
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ctest -C {Debug|Release|RelWithDebInfo|MinSizeRel}
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# or, run the test binary directly
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# (which gives more fine-grained control like filtering):
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<dir-to-glslangtests-in-build-dir>/glslangtests
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```
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Running `runtests` script-backed tests:
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```bash
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cd $SOURCE_DIR/Test && ./runtests
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```
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### Contributing tests
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Test results should always be included with a pull request that modifies
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functionality.
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If you are writing unit tests, please use the Google Test framework and
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place the tests under the `gtests/` directory.
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Integration tests are placed in the `Test/` directory. It contains test input
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and a subdirectory `baseResults/` that contains the expected results of the
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tests. Both the tests and `baseResults/` are under source-code control.
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Google Test runs those integration tests by reading the test input, compiling
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them, and then compare against the expected results in `baseResults/`. The
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integration tests to run via Google Test is registered in various
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`gtests/*.FromFile.cpp` source files. `glslangtests` provides a command-line
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option `--update-mode`, which, if supplied, will overwrite the golden files
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under the `baseResults/` directory with real output from that invocation.
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For more information, please check `gtests/` directory's
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[README](gtests/README.md).
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For the `runtests` script, it will generate current results in the
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`localResults/` directory and `diff` them against the `baseResults/`.
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When you want to update the tracked test results, they need to be
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copied from `localResults/` to `baseResults/`. This can be done by
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the `bump` shell script.
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You can add your own private list of tests, not tracked publicly, by using
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`localtestlist` to list non-tracked tests. This is automatically read
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by `runtests` and included in the `diff` and `bump` process.
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Programmatic Interfaces
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-----------------------
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Another piece of software can programmatically translate shaders to an AST
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using one of two different interfaces:
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* A new C++ class-oriented interface, or
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* The original C functional interface
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The `main()` in `StandAlone/StandAlone.cpp` shows examples using both styles.
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### C++ Class Interface (new, preferred)
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This interface is in roughly the last 1/3 of `ShaderLang.h`. It is in the
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glslang namespace and contains the following.
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```cxx
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const char* GetEsslVersionString();
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const char* GetGlslVersionString();
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bool InitializeProcess();
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void FinalizeProcess();
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class TShader
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bool parse(...);
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void setStrings(...);
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const char* getInfoLog();
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class TProgram
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void addShader(...);
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bool link(...);
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const char* getInfoLog();
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Reflection queries
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```
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See `ShaderLang.h` and the usage of it in `StandAlone/StandAlone.cpp` for more
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details.
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### C Functional Interface (orignal)
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This interface is in roughly the first 2/3 of `ShaderLang.h`, and referred to
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as the `Sh*()` interface, as all the entry points start `Sh`.
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The `Sh*()` interface takes a "compiler" call-back object, which it calls after
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building call back that is passed the AST and can then execute a backend on it.
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The following is a simplified resulting run-time call stack:
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```c
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ShCompile(shader, compiler) -> compiler(AST) -> <back end>
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```
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In practice, `ShCompile()` takes shader strings, default version, and
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warning/error and other options for controlling compilation.
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Basic Internal Operation
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------------------------
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* Initial lexical analysis is done by the preprocessor in
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`MachineIndependent/Preprocessor`, and then refined by a GLSL scanner
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in `MachineIndependent/Scan.cpp`. There is currently no use of flex.
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* Code is parsed using bison on `MachineIndependent/glslang.y` with the
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aid of a symbol table and an AST. The symbol table is not passed on to
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the back-end; the intermediate representation stands on its own.
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The tree is built by the grammar productions, many of which are
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offloaded into `ParseHelper.cpp`, and by `Intermediate.cpp`.
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* The intermediate representation is very high-level, and represented
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as an in-memory tree. This serves to lose no information from the
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original program, and to have efficient transfer of the result from
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parsing to the back-end. In the AST, constants are propogated and
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folded, and a very small amount of dead code is eliminated.
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To aid linking and reflection, the last top-level branch in the AST
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lists all global symbols.
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* The primary algorithm of the back-end compiler is to traverse the
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tree (high-level intermediate representation), and create an internal
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object code representation. There is an example of how to do this
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in `MachineIndependent/intermOut.cpp`.
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* Reduction of the tree to a linear byte-code style low-level intermediate
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representation is likely a good way to generate fully optimized code.
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* There is currently some dead old-style linker-type code still lying around.
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* Memory pool: parsing uses types derived from C++ `std` types, using a
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custom allocator that puts them in a memory pool. This makes allocation
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of individual container/contents just few cycles and deallocation free.
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This pool is popped after the AST is made and processed.
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The use is simple: if you are going to call `new`, there are three cases:
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- the object comes from the pool (its base class has the macro
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`POOL_ALLOCATOR_NEW_DELETE` in it) and you do not have to call `delete`
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- it is a `TString`, in which case call `NewPoolTString()`, which gets
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it from the pool, and there is no corresponding `delete`
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- the object does not come from the pool, and you have to do normal
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C++ memory management of what you `new`
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[cmake]: https://cmake.org/
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[bison]: https://www.gnu.org/software/bison/
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[googletest]: https://github.com/google/googletest
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[bison-gnu-win32]: http://gnuwin32.sourceforge.net/packages/bison.htm
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