OpenGL How to unit test?

Question

Is there a good way to unit test a function or a class using OpenGL commands?

For c++, I know I could make the class a template and pass a class doing direct opengl calls :

namespace myNamespace
{
struct RealOpenglCall
{
  static inline void glVertex2fv( const GLfloat * v)
  { ::glVertex2fv( v ); }
};

template< typename T >
class SomeRendering
{
  public:
    SomeRendering() : v()
    {
      // set v
    }
    void Draw()
    {
      T::glVertex2fv(v);
    }
    GLfloat v[4];
};

}

In C and c++, I could pass function pointers to functions calling opengl functions (then for unit testing passing pointers to mock functions).

I could also link with different library (instead of opengl), but that sounds like a big complication.

So, what are other techniques to unit test code calling opengl functions?

Answer 1

Here is a nice trick i learned a while back. You can use regular old #defines to let you mock all kinds of API functions:

#ifdef _test_
#define glVertex3f(x,y,z)  (mockGlVertex3f((x),(y),(z)))
...
#endif

With a configured preprocessor. There is no need to change your drawing-functions at all. Further: you can implement mockGlVertex3f in such a way that it e.g. checks the arguments or counts the number of calls to it which can then later be checked.