Doxygen guide (#423) (#427)

Author: mergify[bot]

doc/how_to_guides/how_to_guides.rst

@@ -9,3 +9,4 @@ These how-to guides will help you quickly solve specific problems using MoveIt.
    how_to_guide
    how_to_generate_api_doxygen_locally
    how_to_setup_docker_containers_in_ubuntu
+   how_to_write_doxygen

doc/how_to_guides/how_to_write_doxygen.rst

@@ -0,0 +1,79 @@
+How to Contribute Doxygen Comments
+----------------------------------
+
+
+This guide will provide an introduction and overview to good practices for contributing Doxygen comments.
+
+Learning Objectives
+-------------------
+
+- How to write helpful Doxygen Comments
+- Some useful Doxygen Plugins
+
+Instructions
+------------
+When making a contribution to MoveIt (or any code, really), make sure your code is readable and well-commented throughout.
+Using Doxygen comments allows for standardization of documentation and ensures that all contributions have certain information included with them.
+One of the primary benefits of Doxygen is that it allows for automatic generation of API documentation in a consistent, readable format.
+
+
+Plugins exist to automate the creation of Doxygen documentation for
+- `SublimeText <https://packagecontrol.io/packages/DoxyDoxygen>`_
+- `VIM <https://www.vim.org/scripts/script.php?script_id=987>`_
+- `VSCode <https://marketplace.visualstudio.com/items?itemName=cschlosser.doxdocgen>`_
+
+As well as for `many other IDEs <https://www.doxygen.nl/helpers.html>`_.
+
+In general, a Doxygen comment should include a brief description of the thing it is commenting on at the very least.
+Descriptions of the input parameters (if any) as well as the output parameters (if any) is helpful as well.
+
+Several examples are provided below:
+
+
+    .. code-block:: c++
+
+        /** @brief Check for robot self collision. Any collision between any pair of links is checked for, NO collisions are
+        *   ignored.
+        *
+        *  @param req A CollisionRequest object that encapsulates the collision request
+        *  @param res A CollisionResult object that encapsulates the collision result
+        *  @param state The kinematic state for which checks are being made */
+        virtual void checkSelfCollision(const CollisionRequest& req, CollisionResult& res,
+                                        const moveit::core::RobotState& state) const = 0;
+
+
+
+    .. code-block:: c++
+
+        /** @brief A bounding volume hierarchy (BVH) implementation of a tesseract contact manager */
+        class BulletBVHManager
+        {
+        ...
+
+    .. code-block:: c++
+
+        	/** @brief Instantiate and return a instance of a subclass of Type using our
+            *         pluginlib::ClassLoader.
+            * @param class_id A string identifying the class uniquely among
+            *        classes of its parent class.  rviz::GridDisplay might be
+            *        rviz/Grid, for example.
+            * @param error_return If non-NULL and there is an error, *error_return is set to a description of the problem.
+            * @return A new instance of the class identified by class_id, or NULL if there was an error.
+            *
+            * If makeRaw() returns NULL and error_return is not NULL, *error_return will be set.
+            * On success, *error_return will not be changed. */
+         	virtual Type* makeRaw(const QString& class_id, QString* error_return = nullptr) {
+
+These examples serve to provide the types and descriptions of inputs and outputs and capture what the function or class is doing, in brief.
+
+
+Further Reading
+---------------
+
+Feel free to look around in the repositories to see additional examples of Doxygen comments.
+Looking at a similar piece of code to what you will be contributing and seeing its comments is the easiest way to learn.
+
+
+See the how-to guide on how to generate Doxygen API locally :doc:`here <./how_to_generate_api_doxygen_locally>`.
+
+See the Doxygen documentation guide `here <https://www.doxygen.nl/manual/docblocks.html>`_.