What would probably be best on the long run is the idea to also assign a “height” when first processing the shadows, and when drawing the objects, only apply shadows on objects lower than this height. And an object is set to be a little higher than its own shadow. This would probably lead to the best result, where small objects don’t case shadows on objects larger than them. But it would also mean rewriting the way shadows are combined with the scene, adding a bit more shader complexity.

I decided not to use it in the sample, because I though the extra tinkering needed to remove the artifacts might confuse some people.

But mainly, that’s the way I would go about it, if I were to modify the sample.

But, what if we compute a line that stretches across a polygon that is supposed to cast shadow. This line would connect the two most outer points of that polygon, the ones that are on the edges of your shadow. Then we could use that line for calculating shadow using Manders method. Off course such a shadow would partially cover the shadow casting object itself, but then we could draw that object on top of the shadow layer or maybe use a pixel shader to “remove” parts of a shadow that “intersect” with the shadow casting object itself.

Again this is only a rough idea, based on my “common sense logic” and not a deep knowledge of the XNA and shaders. The knowledge which i unfortunately don’t posses (yet)

One way to do this would be to draw the shadow volumes for each edge of the polygon, in the same way as Manders draws shadows for his lines, but depending on the level of detail of that polygon, this could result in a great number of Draw calls (order of tens), as opposed to a single Draw call for the whole object’s shadow, as it happens now. These add up, and may actually hurt performance more than benefit it.

This is one area where DirectX10 geometry shaders would come in handy, as they could be used to generate the shadow’s geometry on the GPU, for any convex shape imaginable. But since XNA is DX9 only, for now I’ll have to stick to doing all this on the CPU.

One other idea would be to move these computations on another thread, and use multi-threading, but this is dangerous territory as well.

The thing that makes me wonder is the optimization of your code. I’m a total noob when it comes to the XNA (although I’d written zillions lines of WinForms code) I wonder if there is a way to get done the heavy lifting by the shaders? I mainly refer to the ConvexHull.DrawShadows(…) method. Mike on his msdn blog draws his 2D shadows using shaders http://blogs.msdn.com/manders/archive/2007/03/14/shadows-in-2d.aspx although for now I can’t make much of his article

As I wrote I’m totally new to the XNA and shaders thing, but it seems like this can be done. Maybe you could spare a few words on this? This would make your code sample completely awesome and maybe we all could learn from it something valuable

P.S. This (http://img237.imageshack.us/my.php?image=shadowsxp7.jpg) picture describe my case.

In advance thanks.