docs: update the coding style information

This hasn't been updated in a long time and from recent discussion on
the mailing list, it's not always clear what's expected.  Hopefully,
this will help a bit.

v2: document function brace placement, per Thomas Helland.

Reviewed-by: Thomas Helland <[email protected]>

1 files changed, 90 insertions, 69 deletions

diff --git a/docs/devinfo.html b/docs/devinfo.html
index e068d87da13..f5113b0bd72 100644
--- a/docs/devinfo.html
+++ b/docs/devinfo.html
@@ -28,97 +28,118 @@
 <h2 id="style">Coding Style</h2>
 
 <p>
-Mesa's code style has changed over the years.  Here's the latest.
+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+Some old parts use a style that's a bit out of date.
+If the guidelines below don't cover something, try following the format of
+existing, neighboring code.
 </p>
 
 <p>
-Comment your code!  It's extremely important that open-source code be
-well documented.  Also, strive to write clean, easily understandable code.
+Basic formatting guidelines
 </p>
 
-<p>
-3-space indentation
-</p>
-
-<p>
-If you use tabs, set them to 8 columns
-</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>
 
-<p>
-Line width: the preferred width to fill comments and code in Mesa is 78
-columns.  Exceptions are sometimes made for clarity (e.g. tabular data is
-sometimes filled to a much larger width so that extraneous carriage returns
-don't obscure the table).
-</p>
+<li>Put a space before/after operators.  For example, <tt>a = b + c;</tt>
+and not <tt>a=b+c;</tt>
 
-<p>
-Brace example:
-</p>
+<li>This GNU indent command generally does the right thing for formatting:
 <pre>
-	if (condition) {
-	   foo;
-	}
-	else {
-	   bar;
-	}
-
-	switch (condition) {
-	case 0:
-	   foo();
-	   break;
-
-	case 1: {
-	   ...
-	   break;
-	}
-
-	default:
-	   ...
-	   break;
-	}
+   indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
 </pre>
 
-<p>
-Here's the GNU indent command which will best approximate my preferred style:
-(Note that it won't format switch statements in the preferred way)
-</p>
+<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>
-	indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
+   /* 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.)
 
-<p>
-Local variable name example:  localVarName (no underscores)
-</p>
-
-<p>
-Constants and macros are ALL_UPPERCASE, with _ between words
-</p>
-
-<p>
-Global variables are not allowed.
-</p>
-
-<p>
-Function name examples:
-</p>
+<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
+   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>
 
-<p>
-Places that are not directly visible to the GL API should prefer the use
-of <tt>bool</tt>, <tt>true</tt>, and
+<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.
-</p>
+
+</ul>
 
 
 <h2 id="submitting">Submitting patches</h2>