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 <thomashelland90@gmail.com>
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<h2 id="style">Coding Style</h2>
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<p>
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Mesa's code style has changed over the years. Here's the latest.
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Mesa is over 20 years old and the coding style has evolved over time.
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Some old parts use a style that's a bit out of date.
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If the guidelines below don't cover something, try following the format of
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existing, neighboring code.
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</p>
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<p>
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Comment your code! It's extremely important that open-source code be
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well documented. Also, strive to write clean, easily understandable code.
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Basic formatting guidelines
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</p>
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<p>
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3-space indentation
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</p>
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<p>
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If you use tabs, set them to 8 columns
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</p>
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<p>
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Line width: the preferred width to fill comments and code in Mesa is 78
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columns. Exceptions are sometimes made for clarity (e.g. tabular data is
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sometimes filled to a much larger width so that extraneous carriage returns
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don't obscure the table).
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</p>
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<p>
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Brace example:
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</p>
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<ul>
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<li>3-space indentation, no tabs.
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<li>Limit lines to 78 or fewer characters. The idea is to prevent line
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wrapping in 80-column editors and terminals. There are exceptions, such
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as if you're defining a large, static table of information.
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<li>Opening braces go on the same line as the if/for/while statement.
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For example:
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<pre>
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if (condition) {
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foo;
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}
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else {
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bar;
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}
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switch (condition) {
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case 0:
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foo();
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break;
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case 1: {
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...
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break;
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}
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default:
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...
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break;
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}
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if (condition) {
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foo;
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} else {
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bar;
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}
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</pre>
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<p>
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Here's the GNU indent command which will best approximate my preferred style:
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(Note that it won't format switch statements in the preferred way)
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</p>
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<li>Put a space before/after operators. For example, <tt>a = b + c;</tt>
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and not <tt>a=b+c;</tt>
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<li>This GNU indent command generally does the right thing for formatting:
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<pre>
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indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
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indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
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</pre>
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<p>
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Local variable name example: localVarName (no underscores)
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</p>
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<p>
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Constants and macros are ALL_UPPERCASE, with _ between words
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</p>
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<p>
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Global variables are not allowed.
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</p>
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<p>
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Function name examples:
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</p>
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<li>Use comments wherever you think it would be helpful for other developers.
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Several specific cases and style examples follow. Note that we roughly
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follow <a href="http://www.stack.nl/~dimitri/doxygen/">Doxygen</a> conventions.
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<br>
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<br>
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Single-line comments:
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<pre>
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glFooBar() - a public GL entry point (in glapi_dispatch.c)
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_mesa_FooBar() - the internal immediate mode function
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save_FooBar() - retained mode (display list) function in dlist.c
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foo_bar() - a static (private) function
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_mesa_foo_bar() - an internal non-static Mesa function
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/* null-out pointer to prevent dangling reference below */
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bufferObj = NULL;
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</pre>
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Or,
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<pre>
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bufferObj = NULL; /* prevent dangling reference below */
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</pre>
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Multi-line comment:
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<pre>
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/* If this is a new buffer object id, or one which was generated but
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* never used before, allocate a buffer object now.
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*/
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</pre>
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We try to quote the OpenGL specification where prudent:
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<pre>
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/* Page 38 of the PDF of the OpenGL ES 3.0 spec says:
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*
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* "An INVALID_OPERATION error is generated for any of the following
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* conditions:
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*
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* * <length> is zero."
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*
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* Additionally, page 94 of the PDF of the OpenGL 4.5 core spec
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* (30.10.2014) also says this, so it's no longer allowed for desktop GL,
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* either.
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*/
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</pre>
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Function comment example:
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<pre>
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/**
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* Create and initialize a new buffer object. Called via the
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* ctx->Driver.CreateObject() driver callback function.
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* \param name integer name of the object
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* \param type one of GL_FOO, GL_BAR, etc.
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* \return pointer to new object or NULL if error
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*/
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struct gl_object *
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_mesa_create_object(GLuint name, GLenum type)
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{
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/* function body */
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}
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</pre>
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<p>
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Places that are not directly visible to the GL API should prefer the use
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of <tt>bool</tt>, <tt>true</tt>, and
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<li>Put the function return type and qualifiers on one line and the function
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name and parameters on the next, as seen above. This makes it easy to use
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<code>grep ^function_name dir/*</code> to find function definitions. Also,
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the opening brace goes on the next line by itself (see above.)
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<li>Function names follow various conventions depending on the type of function:
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<pre>
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glFooBar() - a public GL entry point (in glapi_dispatch.c)
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_mesa_FooBar() - the internal immediate mode function
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save_FooBar() - retained mode (display list) function in dlist.c
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foo_bar() - a static (private) function
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_mesa_foo_bar() - an internal non-static Mesa function
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</pre>
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<li>Constants, macros and enumerant names are ALL_UPPERCASE, with _ between
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words.
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<li>Mesa usually uses camel case for local variables (Ex: "localVarname")
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while gallium typically uses underscores (Ex: "local_var_name").
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<li>Global variables are almost never used because Mesa should be thread-safe.
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<li>Booleans. Places that are not directly visible to the GL API
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should prefer the use of <tt>bool</tt>, <tt>true</tt>, and
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<tt>false</tt> over <tt>GLboolean</tt>, <tt>GL_TRUE</tt>, and
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<tt>GL_FALSE</tt>. In C code, this may mean that
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<tt>#include <stdbool.h></tt> needs to be added. The
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<tt>try_emit_</tt>* methods in src/mesa/program/ir_to_mesa.cpp and
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src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.
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</p>
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</ul>
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<h2 id="submitting">Submitting patches</h2>
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