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Some old parts use a style that's a bit out of date.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.
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:: console
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 <http://www.doxygen.nl>`__
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:
*
* * <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:
.. 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_*`` methods in ``src/mesa/program/ir_to_mesa.cpp`` and
``src/mesa/state_tracker/st_glsl_to_tgsi.cpp`` can serve as examples.
