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git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23467 e7fa87d3-cd2b-0410-9028-fcbf551c1848
147 lines
6.0 KiB
Plaintext
147 lines
6.0 KiB
Plaintext
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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Things left to do: See Todo.txt
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Execution of Standalone Wrapper
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-------------------------------
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There are binaries in the Install/Windows and Install/Linux directories.
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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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Source: Build and run on Linux
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-------------------------------
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A simple bash script "BuildLinux.sh" is provided at the root directory
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to do the build and run a test cases. You will need a recent version of
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bison installed.
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Once the executable is generated, it needs to be dynamically linked with the
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shared object created in lib directory. To achieve that, "cd" to
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StandAlone directory to update the LD_LIBRARY_PATH as follows
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export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:./../glslang/MachineIndependent/lib
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You can also update LD_LIBRARY_PATH in the .cshrc or .bashrc file, depending on
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the shell you are using. You will need to give the complete path of "lib" directory
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in .cshrc or .bashrc files.
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Source: Build and run on Windows
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--------------------------------
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Current development is with Visual Studio verion 11 (2012). The solution
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file is in the project's root directory Standalone.sln.
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Building the StandAlone project (the default) will create glslangValidate.exe and
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copy it into the Test directory and Install directory. This allows local
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test scripts to use either the debug or release version, whichever was
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built last.
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Windows execution and testing is generally done from within a cygwin
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shell.
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Note: Despite appearances, the use of a DLL is currently disabled; it
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simply makes a standalone executable from a statically linked library.
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Basic external programmatic interface
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-------------------------------------
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Another piece of software can programmatically translate shaders to an AST
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using the C-style ShInitialize(), ShCompile(), et. al. interface. The main() in
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StandAlone/StandAlone.cpp shows an example way of using these.
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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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ShCompile(shader, compiler) -> compiler(AST) -> <back end>
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In practice, ShCompile() takes shader strings, default version, and
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warning/error and other options for controling compilation.
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Testing
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-------
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"Test" is an active test directory that contains test input and a
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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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Executing the script ./runtests will generate current results in
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the 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
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There are some tests borrowed from LunarGLASS. If LunarGLASS is
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missing, those tests just won't run.
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Basic Internal Operation
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------------------------
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- Initial lexical analysis is done be 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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