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  <title>Coding Style</title>
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<div class="header">
  <h1>The Mesa 3D Graphics Library</h1>
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<h1>Coding Style</h1>

<p>
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Some old parts use a style that's a bit out of date.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.
</p>

<p>
Basic formatting guidelines
</p>

<ul>
<li>3-space indentation, no tabs.
<li>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.
<li>Opening braces go on the same line as the if/for/while statement.
For example:
<pre>
   if (condition) {
      foo;
   } else {
      bar;
   }
</pre>

<li>Put a space before/after operators.  For example, <tt>a = b + c;</tt>
and not <tt>a=b+c;</tt>

<li>This GNU indent command generally does the right thing for formatting:
<pre>
   indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
</pre>

<li>Use comments wherever you think it would be helpful for other developers.
Several specific cases and style examples follow.  Note that we roughly
follow <a href="http://www.stack.nl/~dimitri/doxygen/">Doxygen</a> conventions.
<br>
<br>
Single-line comments:
<pre>
   /* null-out pointer to prevent dangling reference below */
   bufferObj = NULL;
</pre>
Or,
<pre>
   bufferObj = NULL;  /* prevent dangling reference below */
</pre>
Multi-line comment:
<pre>
   /* If this is a new buffer object id, or one which was generated but
    * never used before, allocate a buffer object now.
    */
</pre>
We try to quote the OpenGL specification where prudent:
<pre>
   /* 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.
    */
</pre>
Function comment example:
<pre>
   /**
    * 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 */
   }
</pre>

<li>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
<code>grep ^function_name dir/*</code> to find function definitions.  Also,
the opening brace goes on the next line by itself (see above.)

<li>Function names follow various conventions depending on the type of function:
<pre>
   glFooBar()       - a public GL entry point (in glapi_dispatch.c)
   _mesa_FooBar()   - the internal immediate mode function
   save_FooBar()    - retained mode (display list) function in dlist.c
   foo_bar()        - a static (private) function
   _mesa_foo_bar()  - an internal non-static Mesa function
</pre>

<li>Constants, macros and enumerant names are ALL_UPPERCASE, with _ between
words.
<li>Mesa usually uses camel case for local variables (Ex: "localVarname")
while gallium typically uses underscores (Ex: "local_var_name").
<li>Global variables are almost never used because Mesa should be thread-safe.

<li>Booleans.  Places that are not directly visible to the GL API
should prefer the use of <tt>bool</tt>, <tt>true</tt>, and
<tt>false</tt> over <tt>GLboolean</tt>, <tt>GL_TRUE</tt>, and
<tt>GL_FALSE</tt>.  In C code, this may mean that
<tt>#include &lt;stdbool.h&gt;</tt> needs to be added.  The
<tt>try_emit_</tt>* methods in src/mesa/program/ir_to_mesa.cpp and
src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.

</ul>
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