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 Some old parts use a style that’s a bit out of date.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¶
Add this to your .vimrc
to automatically format any C & C++ file
(that has a .clang-format config) when you save it:
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¶
Add this to your .emacs
to automatically format any C & C++ file
(that has a .clang-format config) when you save it:
(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
to install clang-format through Emacs instead.
git pre-commit
hook¶
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
:
shopt -s globstar
git clang-format $upstream -- $(grep -E '^[^#]' .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:
if (condition) { foo; } else { bar; }
Put a space before/after operators. For example,
a = b + c;
and nota=b+c;
This GNU indent command generally does the right thing for formatting:
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:
/* null-out pointer to prevent dangling reference below */ bufferObj = NULL;
Or,
bufferObj = NULL; /* prevent dangling reference below */
Multi-line comment:
/* 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:
/* 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: * * * <length> 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:
/** * 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
glapi_dispatch.c
)_mesa_FooBar()
the internal immediate mode function
save_FooBar()
retained mode (display list) function in
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
, andfalse
overGLboolean
,GL_TRUE
, andGL_FALSE
. In C code, this may mean that#include <stdbool.h>
needs to be added. Thetry_emit_*
methodsrc/mesa/state_tracker/st_glsl_to_tgsi.cpp
can serve as an example.