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      5   <title>Coding Style</title>
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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>
     20 Mesa is over 20 years old and the coding style has evolved over time.
     21 Some old parts use a style that's a bit out of date.
     22 
     23 Different sections of mesa can use different coding style as set in the local
     24 EditorConfig (.editorconfig) and/or Emacs (.dir-locals.el) file.
     25 
     26 Alternatively the following is applicable.
     27 
     28 If the guidelines below don't cover something, try following the format of
     29 existing, neighboring code.
     30 </p>
     31 
     32 <p>
     33 Basic 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
     39 wrapping in 80-column editors and terminals.  There are exceptions, such
     40 as 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.
     42 For 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>
     52 and 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.
     60 Several specific cases and style examples follow.  Note that we roughly
     61 follow <a href="https://www.stack.nl/~dimitri/doxygen/">Doxygen</a> conventions.
     62 <br>
     63 <br>
     64 Single-line comments:
     65 <pre>
     66    /* null-out pointer to prevent dangling reference below */
     67    bufferObj = NULL;
     68 </pre>
     69 Or,
     70 <pre>
     71    bufferObj = NULL;  /* prevent dangling reference below */
     72 </pre>
     73 Multi-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>
     79 We 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>
     93 Function 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
    110 name 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,
    112 the 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
    124 words.
    125 <li>Mesa usually uses camel case for local variables (Ex: "localVarname")
    126 while 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
    130 should 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
    135 src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.
    136 
    137 </ul>
    138 </p>
    139 
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