Coding Style

# The Mesa 3D Graphics Library

# Coding Style

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 Some old parts use a style that's a bit out of date.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

Basic formatting guidelines

- 3-space indentation, no tabs.
- 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.
- Opening braces go on the same line as the if/for/while statement. For example:

         if (condition) {
            foo;
         } else {
            bar;
         }

- Put a space before/after operators. For example, `a = b + c;` and not `a=b+c;`
- This GNU indent command generally does the right thing for formatting:

         indent -br -i3 -npcs --no-tabs infile.c -o outfile.c

- Use comments wherever you think it would be helpful for other developers. Several specific cases and style examples follow. Note that we roughly follow Doxygen conventions.
  Single-line comments:

         /* null-out pointer to prevent dangling reference below */
         bufferObj = NULL;

  Or,

         bufferObj = NULL;  /* prevent dangling reference below */

  Multi-line comment:

         /* If this is a new buffer object id, or one which was generated but
          * never used before, allocate a buffer object now.
          */

  We try to quote the OpenGL specification where prudent:

         /* 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:
          *
          *     *  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.
          */

  Function comment example:

         /**
          * 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 */
         }

- 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 `grep ^function_name dir/*` to find function definitions. Also, the opening brace goes on the next line by itself (see above.)
- Function names follow various conventions depending on the type of 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

- Constants, macros and enum names are ALL_UPPERCASE, with _ between words.
- Mesa usually uses camel case for local variables (Ex: "localVarname") while gallium typically uses underscores (Ex: "local_var_name").
- Global variables are almost never used because Mesa should be thread-safe.
- Booleans. Places that are not directly visible to the GL API should prefer the use of `bool`, `true`, and `false` over `GLboolean`, `GL_TRUE`, and `GL_FALSE`. In C code, this may mean that `#include <stdbool.h>` needs to be added. The `try_emit_`* methods in src/mesa/program/ir_to_mesa.cpp and src/mesa/state_tracker/st_glsl_to_tgsi.cpp can serve as examples.