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1Coding Style
2============
3
4Mesa is over 20 years old and the coding style has evolved over time.
5Some old parts use a style that's a bit out of date. Different sections
6of mesa can use different coding style as set in the local EditorConfig
7(.editorconfig) and/or Emacs (.dir-locals.el) file. Alternatively the
8following is applicable. If the guidelines below don't cover something,
9try following the format of existing, neighboring code.
10
11Basic formatting guidelines
12
13-  3-space indentation, no tabs.
14-  Limit lines to 78 or fewer characters. The idea is to prevent line
15   wrapping in 80-column editors and terminals. There are exceptions,
16   such as if you're defining a large, static table of information.
17-  Opening braces go on the same line as the if/for/while statement. For
18   example:
19
20   .. code-block:: c
21
22      if (condition) {
23         foo;
24      } else {
25         bar;
26      }
27
28-  Put a space before/after operators. For example, ``a = b + c;`` and
29   not ``a=b+c;``
30-  This GNU indent command generally does the right thing for
31   formatting:
32
33   .. code-block:: console
34
35      indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
36
37-  Use comments wherever you think it would be helpful for other
38   developers. Several specific cases and style examples follow. Note
39   that we roughly follow `Doxygen <http://www.doxygen.nl>`__
40   conventions.
41
42   Single-line comments:
43
44   .. code-block:: c
45
46      /* null-out pointer to prevent dangling reference below */
47      bufferObj = NULL;
48
49   Or,
50
51   .. code-block:: c
52
53      bufferObj = NULL;  /* prevent dangling reference below */
54
55   Multi-line comment:
56
57   .. code-block:: c
58
59      /* If this is a new buffer object id, or one which was generated but
60       * never used before, allocate a buffer object now.
61       */
62
63   We try to quote the OpenGL specification where prudent:
64
65   .. code-block:: c
66
67      /* Page 38 of the PDF of the OpenGL ES 3.0 spec says:
68       *
69       *     "An INVALID_OPERATION error is generated for any of the following
70       *     conditions:
71       *
72       *     * <length> is zero."
73       *
74       * Additionally, page 94 of the PDF of the OpenGL 4.5 core spec
75       * (30.10.2014) also says this, so it's no longer allowed for desktop GL,
76       * either.
77       */
78
79   Function comment example:
80
81   .. code-block:: c
82
83      /**
84       * Create and initialize a new buffer object.  Called via the
85       * ctx->Driver.CreateObject() driver callback function.
86       * \param  name  integer name of the object
87       * \param  type  one of GL_FOO, GL_BAR, etc.
88       * \return  pointer to new object or NULL if error
89       */
90      struct gl_object *
91      _mesa_create_object(GLuint name, GLenum type)
92      {
93         /* function body */
94      }
95
96-  Put the function return type and qualifiers on one line and the
97   function name and parameters on the next, as seen above. This makes
98   it easy to use ``grep ^function_name dir/*`` to find function
99   definitions. Also, the opening brace goes on the next line by itself
100   (see above.)
101-  Function names follow various conventions depending on the type of
102   function:
103
104   +---------------------+------------------------------------------+
105   | Convention          | Explanation                              |
106   +=====================+==========================================+
107   | ``glFooBar()``      | a public GL entry point (in              |
108   |                     | :file:`glapi_dispatch.c`)                |
109   +---------------------+------------------------------------------+
110   | ``_mesa_FooBar()``  | the internal immediate mode function     |
111   +---------------------+------------------------------------------+
112   | ``save_FooBar()``   | retained mode (display list) function in |
113   |                     | :file:`dlist.c`                          |
114   +---------------------+------------------------------------------+
115   | ``foo_bar()``       | a static (private) function              |
116   +---------------------+------------------------------------------+
117   | ``_mesa_foo_bar()`` | an internal non-static Mesa function     |
118   +---------------------+------------------------------------------+
119
120-  Constants, macros and enum names are ``ALL_UPPERCASE``, with \_
121   between words.
122-  Mesa usually uses camel case for local variables (Ex:
123   ``localVarname``) while Gallium typically uses underscores (Ex:
124   ``local_var_name``).
125-  Global variables are almost never used because Mesa should be
126   thread-safe.
127-  Booleans. Places that are not directly visible to the GL API should
128   prefer the use of ``bool``, ``true``, and ``false`` over
129   ``GLboolean``, ``GL_TRUE``, and ``GL_FALSE``. In C code, this may
130   mean that ``#include <stdbool.h>`` needs to be added. The
131   ``try_emit_*`` methods in ``src/mesa/program/ir_to_mesa.cpp`` and
132   ``src/mesa/state_tracker/st_glsl_to_tgsi.cpp`` can serve as examples.
133