How to achieve drawing a simple rectangle?

So I'd like to have a simple rectangle drawn instead the rounded corners one.
I am having trouble in finding any method to do this, and also tried to extend the TutoShowcase proved to be a hellish task, as its construction is almost non-extendable.

So is there any simple way other than actually downloading and manually changing the lib my self, which I'd like to avoid if possible.

Cheers

Start by reading TutoShowcase's construction and the code that draws its rounded corners; the issue does not name a file or test. Trace how the showcase view is configured, then determine whether a simple rectangle can be selected without manually modifying the library. Done means the library offers a supported way to display a rectangle and the behavior is verified on Android.

Written by the indexing model from the issue text.