# Simulating wind (vertex bending)

Right now I'm using the Crytek vegetation bending technique, vertex colors control how much force is applied to the branches, leafs and trunks. I have it working and it looks nice but I'm just using random wind so it's all over the place.

Here is the code I use for the wind on the CPU, this gets passed of the vertex shader where the bending happens:

    // Change wind every second, and smoothly interpolate to the new strength/direction.
Dim timeEllapsed As Single = CType(gametime.ElapsedGameTime.TotalSeconds, Single)
_Time += timeEllapsed
timeSinceLastThing -= timeEllapsed
If timeSinceLastThing < 0F Then
lastWindSpeed = newWindSpeed
Dim x As Single = CType(random.NextDouble(), Single)
x = CType(Math.Pow(x, 3), Single)
Dim y As Single = CType(random.NextDouble(), Single)
y = CType(Math.Pow(y, 3), Single)
newWindSpeed = New Vector2(x * 2.0F - 1.0F, y * 2.0F - 1.0F)
newWindSpeed *= 0.9F
timeSinceLastThing += 1.0F
End If
currentWindSpeed = Vector2.SmoothStep(newWindSpeed, lastWindSpeed, timeSinceLastThing)


It's nice and flowy so that's not an issue, it just doesn't really gust and stuff the same way wind does. I'm just wondering if anyone knows of a better way of making nice swaying wind? Or will I just have to tweak it till I find what I'm after?

• i have a question, does it only displaces the bullet on teh x-axis curve but teh y-axis as well? – whale Mar 1 at 23:43
• Have you thought about maybe using a gerstner function to simulate more gust like behaviour. The gerstner wave in this case would be used to calculate force, rather than displacement. Seeing you already have the amount of force worked out for the actual vegetation. The Gerstner formula is used for wave simulation, and it might be interesting experiment here. – ErnieDingo Mar 2 at 1:35
• Thanks for that, while im not working on this right now im slowly porting all my code to c++. If you want to make an answer ill accept it. – Justin William Stanley Bryant May 13 at 23:32