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 Some old parts use a style that’s a bit out of date.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:
   *
   *     * <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.
   */
  

  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.