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11  <h1>The Mesa 3D Graphics Library</h1>
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16
17<h1>Coding Style</h1>
18
19<p>
20Mesa is over 20 years old and the coding style has evolved over time.
21Some old parts use a style that's a bit out of date.
22
23Different sections of mesa can use different coding style as set in the local
24EditorConfig (.editorconfig) and/or Emacs (.dir-locals.el) file.
25
26Alternatively the following is applicable.
27
28If the guidelines below don't cover something, try following the format of
29existing, neighboring code.
30</p>
31
32<p>
33Basic formatting guidelines
34</p>
35
36<ul>
37<li>3-space indentation, no tabs.
38<li>Limit lines to 78 or fewer characters.  The idea is to prevent line
39wrapping in 80-column editors and terminals.  There are exceptions, such
40as if you're defining a large, static table of information.
41<li>Opening braces go on the same line as the if/for/while statement.
42For example:
43<pre>
44   if (condition) {
45      foo;
46   } else {
47      bar;
48   }
49</pre>
50
51<li>Put a space before/after operators.  For example, <tt>a = b + c;</tt>
52and not <tt>a=b+c;</tt>
53
54<li>This GNU indent command generally does the right thing for formatting:
55<pre>
56   indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
57</pre>
58
59<li>Use comments wherever you think it would be helpful for other developers.
60Several specific cases and style examples follow.  Note that we roughly
61follow <a href="https://www.stack.nl/~dimitri/doxygen/">Doxygen</a> conventions.
62<br>
63<br>
64Single-line comments:
65<pre>
66   /* null-out pointer to prevent dangling reference below */
67   bufferObj = NULL;
68</pre>
69Or,
70<pre>
71   bufferObj = NULL;  /* prevent dangling reference below */
72</pre>
73Multi-line comment:
74<pre>
75   /* If this is a new buffer object id, or one which was generated but
76    * never used before, allocate a buffer object now.
77    */
78</pre>
79We try to quote the OpenGL specification where prudent:
80<pre>
81   /* Page 38 of the PDF of the OpenGL ES 3.0 spec says:
82    *
83    *     "An INVALID_OPERATION error is generated for any of the following
84    *     conditions:
85    *
86    *     * <length> is zero."
87    *
88    * Additionally, page 94 of the PDF of the OpenGL 4.5 core spec
89    * (30.10.2014) also says this, so it's no longer allowed for desktop GL,
90    * either.
91    */
92</pre>
93Function comment example:
94<pre>
95   /**
96    * Create and initialize a new buffer object.  Called via the
97    * ctx->Driver.CreateObject() driver callback function.
98    * \param  name  integer name of the object
99    * \param  type  one of GL_FOO, GL_BAR, etc.
100    * \return  pointer to new object or NULL if error
101    */
102   struct gl_object *
103   _mesa_create_object(GLuint name, GLenum type)
104   {
105      /* function body */
106   }
107</pre>
108
109<li>Put the function return type and qualifiers on one line and the function
110name and parameters on the next, as seen above.  This makes it easy to use
111<code>grep ^function_name dir/*</code> to find function definitions.  Also,
112the opening brace goes on the next line by itself (see above.)
113
114<li>Function names follow various conventions depending on the type of function:
115<pre>
116   glFooBar()       - a public GL entry point (in glapi_dispatch.c)
117   _mesa_FooBar()   - the internal immediate mode function
118   save_FooBar()    - retained mode (display list) function in dlist.c
119   foo_bar()        - a static (private) function
120   _mesa_foo_bar()  - an internal non-static Mesa function
121</pre>
122
123<li>Constants, macros and enum names are ALL_UPPERCASE, with _ between
124words.
125<li>Mesa usually uses camel case for local variables (Ex: "localVarname")
126while gallium typically uses underscores (Ex: "local_var_name").
127<li>Global variables are almost never used because Mesa should be thread-safe.
128
129<li>Booleans.  Places that are not directly visible to the GL API
130should prefer the use of <tt>bool</tt>, <tt>true</tt>, and
131<tt>false</tt> over <tt>GLboolean</tt>, <tt>GL_TRUE</tt>, and
132<tt>GL_FALSE</tt>.  In C code, this may mean that
133<tt>#include &lt;stdbool.h&gt;</tt> needs to be added.  The
134<tt>try_emit_</tt>* methods in src/mesa/program/ir_to_mesa.cpp and
135src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.
136
137</ul>
138</p>
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