The attached patch adds support for styled cosmetic lines in the graphics engine of the Win32 subsystem. With one pixel width currently, but I'm interested in adding support for thick lines generally (http://reactos.org/bugzilla/show_bug.cgi?id=2761) if wanted.
Please, a GDI guru of ROS should check if this is okay. I'm still not very familiar with all the GDI internals.
It's not the fastest way doing it with PutPixel for Horizontal and Vertical lines for sure. There is still need for optimization.
Futhermore this bug fixes test gdi32:pen