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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>Coding Style</title>
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<div class="header">
The Mesa 3D Graphics Library
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<div class="content">
<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Some old parts use a style that's a bit out of date.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, <code>a = b + c;</code>
and not <code>a=b+c;</code>
<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>
<p>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="https://www.stack.nl/~dimitri/doxygen/">Doxygen</a> conventions.
</p>
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 enum names are <code>ALL_UPPERCASE</code>, with _
between words.
<li>Mesa usually uses camel case for local variables (Ex:
<code>localVarname</code>) while gallium typically uses underscores (Ex:
<code>local_var_name</code>).
<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 <code>bool</code>, <code>true</code>, and
<code>false</code> over <code>GLboolean</code>, <code>GL_TRUE</code>, and
<code>GL_FALSE</code>. In C code, this may mean that
<code>#include <stdbool.h></code> needs to be added. The
<code>try_emit_</code>* methods in <code>src/mesa/program/ir_to_mesa.cpp</code>
and <code>src/mesa/state_tracker/st_glsl_to_tgsi.cpp</code> can serve as
examples.
</ul>
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