docs/codingstyle.html

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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  21 Some old parts use a style that's a bit out of date.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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