wumpus-basic

Copperbox revision 2177.

I've changed the Image and ImageAns types so the answer of an Image is always parametric on the unit u.

Possibly this will be restricting - but it seems it will be the only way to change the units of an Image. So far the Image answers in Wumpus are all parametric on unit: BoundingBox - answer of BoundedGraphic, Vec2 - answer of AdvGraphic, Ellispe and the other shapes.