Coding Style

Mesa is over 20 years old and the coding style has evolved over time. Some old parts use a style that's a bit out of date. Different sections of mesa can use different coding style as set in the local EditorConfig (.editorconfig) and/or Emacs (.dir-locals.el) file. Alternatively the following is applicable. If the guidelines below don't cover something, try following the format of existing, neighboring code.

clang-format

A growing number of drivers and components are adopting clang-format to standardize the formatting and make it easy for everyone to apply it.

You can re-format the code for the components that have opted-in to the formatting enforcement (listed in .clang-format-include) by simply running ninja -C build/ clang-format.

Since mass-reformatting commits can be an annoying extra jump to go through when looking at git blame, you can configure it to ignore them by running::

git config blame.ignoreRevsFile .git-blame-ignore-revs

Most code editors also support automatically formatting code as you write it; check your editor or its plug-ins to see how to enable this.

Vim

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Add this to your .vimrc to automatically format any C & C++ file (that has a .clang-format config) when you save it:

.. code:: vim

augroup ClangFormatOnSave au!

 function! ClangFormatOnSave()
   " Only format files that have a .clang-format in a parent folder
   if !empty(findfile('.clang-format', '.;'))
     let l:formatdiff = 1 " Only format lines that have changed
     py3f /usr/share/clang/clang-format.py
   endif
 endfunction

 autocmd BufWritePre *.h,*.c,*.cc,*.cpp call ClangFormatOnSave()

augroup END

If /usr/share/clang/clang-format.py doesn't exist, try /usr/share/clang/clang-format-$CLANG_VERSION/clang-format.py (replacing $CLANG_VERSION with your clang version). If your distro has put the file somewhere else, look through the files in the package providing clang-format.

Emacs

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Add this to your .emacs to automatically format any C & C++ file (that has a .clang-format config) when you save it:

.. code:: emacs

(load "/usr/share/clang/clang-format.el")

(defun clang-format-save-hook-for-this-buffer () "Create a buffer local save hook." (add-hook 'before-save-hook (lambda () (when (locate-dominating-file "." ".clang-format") (clang-format-buffer)) ;; Continue to save. nil) nil ;; Buffer local hook. t))

;; Run this for each mode you want to use the hook. (add-hook 'c-mode-hook (lambda () (clang-format-save-hook-for-this-buffer))) (add-hook 'c++-mode-hook (lambda () (clang-format-save-hook-for-this-buffer)))

If /usr/share/clang/clang-format.el doesn't exist, look through the files in the package providing clang-format in your distro. If you can't find anything (e.g. on Debian/Ubuntu), refer to this StackOverflow answer <https://stackoverflow.com/questions/59690583/how-do-you-use-clang-format-on-emacs-ubuntu/59850773#59850773>__ to install clang-format through Emacs instead.

git pre-commit hook

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If your editor doesn't support this, or if you don't want to enable it, you can always just run ninja clang-format to format everything, or add a pre-commit hook that runs this automatically whenever you git commit by adding the following in your .git/hooks/pre-commit:

.. code:: sh

shopt -s globstar git clang-format $upstream -- $(grep -E '^[1]' .clang-format-include)

replace $upstream with the name of the remote tracking upstream mesa

if you don't know, it's probably origin

Basic formatting guidelines

• 3-space indentation, no tabs.

• Limit lines to 78 or fewer characters. The idea is to prevent line wrapping in 80-column editors and terminals. There are exceptions, such as if you're defining a large, static table of information.

• Opening braces go on the same line as the if/for/while statement. For example:

  .. code-block:: c

  if (condition) { foo; } else { bar; }

• Put a space before/after operators. For example, a = b + c; and not a=b+c;

• This GNU indent command generally does the right thing for formatting:

  .. code-block:: sh

  indent -br -i3 -npcs --no-tabs infile.c -o outfile.c

• Use comments wherever you think it would be helpful for other developers. Several specific cases and style examples follow. Note that we roughly follow Doxygen conventions.

  Single-line comments:

  .. code-block:: c

  /* null-out pointer to prevent dangling reference below */ bufferObj = NULL;

  Or,

  .. code-block:: c

  bufferObj = NULL; /* prevent dangling reference below */

  Multi-line comment:

  .. code-block:: c

  /* If this is a new buffer object id, or one which was generated but * never used before, allocate a buffer object now. */

  We try to quote the OpenGL specification where prudent:

  .. code-block:: c

  /* Page 38 of the PDF of the OpenGL ES 3.0 spec says: * * "An INVALID_OPERATION error is generated for any of the following * conditions: * * * is zero." * * Additionally, page 94 of the PDF of the OpenGL 4.5 core spec * (30.10.2014) also says this, so it's no longer allowed for desktop GL, * either. */

  Function comment example:

  .. code-block:: c

  /** * Create and initialize a new buffer object. Called via the * ctx->Driver.CreateObject() driver callback function. * \param name integer name of the object * \param type one of GL_FOO, GL_BAR, etc. * \return pointer to new object or NULL if error / struct gl_object * _mesa_create_object(GLuint name, GLenum type) { / function body */ }

• Put the function return type and qualifiers on one line and the function name and parameters on the next, as seen above. This makes it easy to use grep ^function_name dir/* to find function definitions. Also, the opening brace goes on the next line by itself (see above.)

• Function names follow various conventions depending on the type of function:

  +---------------------+------------------------------------------+ | Convention | Explanation | +=====================+==========================================+ | glFooBar() | a public GL entry point (in | | | :file:glapi_dispatch.c) | +---------------------+------------------------------------------+ | _mesa_FooBar() | the internal immediate mode function | +---------------------+------------------------------------------+ | save_FooBar() | retained mode (display list) function in | | | :file:dlist.c | +---------------------+------------------------------------------+ | foo_bar() | a static (private) function | +---------------------+------------------------------------------+ | _mesa_foo_bar() | an internal non-static Mesa function | +---------------------+------------------------------------------+

• Constants, macros and enum names are ALL_UPPERCASE, with _ between words.

• Mesa usually uses camel case for local variables (Ex: localVarname) while Gallium typically uses underscores (Ex: local_var_name).

• Global variables are almost never used because Mesa should be thread-safe.

• Booleans. Places that are not directly visible to the GL API should prefer the use of bool, true, and false over GLboolean, GL_TRUE, and GL_FALSE. In C code, this may mean that #include <stdbool.h> needs to be added. The try_emit_* method src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as an example.

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