Improve Instance culling technique using a quadtree or something similar

[prock]

The more instances you have on a map the more the framerate suffers. We need to implement a new culling technique to sort and cull instances that do not exist in the view area.

Discussions and a profile can be found here:  http://forums.parpg.net/index.php?topic=570.0 and some more discussions here:  http://logs.unknown-horizons.org/%23fife/%23fife.2009-Wed-22.log

FIFE currently uses a quadtree to sort instances for instance selection. Why not make use of the quadtree for rendering also? Perhaps a new data structure is in order.

[phoku]

I was working on that one.

Solution is inside the view_performance branch.

Using QuadTree? to spatially sort the onscreen images:

 http://fife.trac.cvsdude.com/engine/browser/branches/active/view_performance/engine/core/view/layercache.cpp

Using it from the Camera:

 http://fife.trac.cvsdude.com/engine/browser/branches/active/view_performance/engine/core/view/camera.cpp

Things get messy with zooming+rotation though, so it's not finished.

[helios2000]

(In [3287]) * Merged the view performance branch back into trunk. closes #419