HS: mouse picking simplicity

One of the nicest things about XNA in comparison to Java3D is the flexibility afforded when drawing and picking, since you have complete control of the pipeline. For picking, this means that you can implement a lot of low-level smarts that make your job easier.

Whereas in Java3D, a pick ray would pick everything in the scene, even stuff that was occluded or facing the wrong way, with XNA you can implement specific pick tests for each of your objects and pick in whatever order you like. So for now, I run a pick on my Scene, which calls a pick on the Planet, which only calls a pick on the list of Sites (the cities and zones and so on). Later I am sure I'll have to adjust this to encompass the planet too (for adding new bases, and arbitrary waypoints for aircraft).

My picking architecture is to pass a MouseMode and a PickMode through to each object so it can decide whether it can be picked at all, and what the relevant pick action is. Cities can only be picked with the "hover"£ PickMode, which returns their label to be displayed, unless the city has a base in it, in which case they also accept "right click" PickModes, with the pick action being a context menu to display. The MouseMode part is used for things like squad deployment. As you can see here:

By clicking the green button on the Team window, I set my MouseMode to a "squad select destination" mouse mode. This overrides the regular picking behaviour, and it itself knows that squads can currently only have their destination set to a Site, no matter what else is available for picking.