twist and shear base altitude ?

[Dune]

Can anyone enlighten me on what the base altitude in the twist and shear shader exactly does? And how it gets its data? If added to a testspike it only shifts the spike from left to right...

[Tangled-Universe]

...from left to right...?
That doesn't make sense to me?

[Dune]

The whole spike, not the top. Like the basis is well below the ground... It tilts the same way though.

[Henry Blewer]

I have been linking the twist and shear through/by a distribution shader to control the altitude and slope. It's not a good solution.

From the WIKI. http://www.planetside.co.uk/wiki/index.php/Twist_and_Shear_Shader

[Dune]

Yeah, that's what I do too (works fine for me), but I just wondered what the base altitude is/does...

[Henry Blewer]

From what I understand for the explanation, it is an adjustment of the beginning (lowest) altitude  the effect begins to alter the terrain.

[Matt]

The shear effect displaces the terrain horizontally. To create the shear effect, the amount of displacement varies with altitude. There must be some altitude where the displacement is 0, and this is the base altitude. Above base altitude the displacement is positive in some direction; below base altitude the displacement is negative.

Maybe one day we'll add the "twist" feature to the Twist and Shear Shader, but right now it only does "shear".

[Henry Blewer]

Then everything above the base altitude gets transposed by the effect? Say I set the base altitude to 50 m. Below 50 m there is not an effect?

[Matt]

The effect continues below the base altitude. Imagine a vertical line. Put a pivot somewhere along the line - this is the base altitude. At the pivot, nothing moves. If I rotate the line so that the top moves to the right, if the line is still a straight line then below the pivot it moves to the left.

The shear effect isn't a rotation, it's just a horizontal displacement, but the principle is the same. The base altitude is the altitude where you want the pivot to be. The effect continues below the pivot.

Matt

[Henry Blewer]

That is a very good explanation Matt. Thank you.

[Dune]

Thanks very much, Matt. That explains a lot.