Marco Tarini's Windy Flora

As seen in The Last Days mod for Mount&Blade 1.011, Marco Tarini (mtarini), the creator of OpenBRF added a good bunch of custom shaders, that he released in the latest patch. This is an interesting bit of a vertex shader allowing us to make life-like waving trees and grass:

   float windAmount = sin(time_var*0.1014) + cos(time_var*0.1413);
   windAmount*=windAmount; 
   float2 treePos = float2 (matWorld._m03, matWorld._m13) + vPosition.xy;
   float t2 = time_var + dot( treePos , float2(2.5,1.5)) ;
   float windPhase = sin(t2*3.9)*cos(t2*2.3);
	vPosition.xy += float2(0.018,0.018) // *(vPosition.z+50.0)
				    *windPhase*(windAmount+0.2)
                   *vColor.w; // distance from ground stored in alpha channes with openbrf easteregg! ;)

Take a look to how the vertex height is encoded in the vertex color alpha channel of the resource file, passed as float from the game. Smart trick!

[edit] Source

Download the 3.1 patch from ModDB for the complete shader file:

http://www.moddb.com/mods/the-last-days/downloads/the-last-days-patch-from-30-to-31

[edit] Preview

The results are something like this:

http://www.youtube.com/watch?v=mWKgCEvbG6w