I'm working on a fairly large project that involves 3D drawing, and I want to add some visualizers (for example, to see the bounding boxes of the objects) to make debugging easier. However, I'm having a problem in deciding how to go about this.
One option would be to create a public function to draw the visualizers, and call this function when I enable debugging from the UI. This would have the advantage of not modifying the existing functions, but extending the class with a new function. The disadvantage would be "creating dependencies", as one of my colleagues said, we would need to modify the base class, and all the deriving classes to add this function.
Another option would be to modify the existing drawing function so that it handles the drawing of the visualizers. This hides the implementation details, but also it seems to me it makes the code less modular.
Yet another option is extending the class, adding the visualizer in the drawing function, and swapping classes when debugging is enabled. Mixins would be of help, but C++ doesn't support that.
What would be the best approach to do this? I'm looking for a solution that is modular and respects the SOLID principles.
It looks like you are looking for the "Delegation Pattern". See http://en.wikipedia.org/wiki/Delegation_pattern
In software engineering, the delegation pattern is a design pattern in object-oriented programming where an object, instead of performing one of its stated tasks, delegates that task to an associated helper object. There is an Inversion of Responsibility in which a helper object, known as a delegate, is given the responsibility to execute a task for the delegator.
See also http://best-practice-software-engineering.ifs.tuwien.ac.at/patterns/delegation.html