Rotate Gradient background?

[MisterMaker]

So I was looking around if I could rotate the gradient background 45 degrees just like some other CAD program have.
And I eventually found this:
https://github.com/FreeCAD/FreeCAD/blob ... adient.cpp
As far as my coding understanding goes, it seems to draw a line between points in the window to set the gradient?
Wonder if it is easy to modify it to add a 45 degree offset, by using a macro.