DTE tutorial part 4 : Adding height information to the texture                                                  Feb 2000
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Remember what we were after ? We want the colour to go from light to dark near the waterline.
We can make it darker ourselves by pushing the slider DIFFUSION to a lower percentage and lighter with a higher percentage.
But to get the effect we're after we'll connect DIFFUSION to an ALPHA channel of a second texture.

Click B for Diffusion : some random texture will show up.Click the down arrow top right of this texture and select Basic . 
Next select the second Basic Altitude (see picture below). Change the mapping mode to World Space if it's anything else.

The resulting material gets a lower diffusion value (darker colour) where the middle part (the ALPHA channel) of the Basic altitude texture is darker and a higher one (lighter colour) where it's brighter. Simple !

Driving the DIFFUSION with a second texture : 'Basic Altitude'

Why is Basic Altitude height dependent ? I'll explain all that when we get to the Filter settings.

 
Changing the scale of the Texture The result in the preview looks very dark right now, because the change from bright to dark is rather large and starts pretty high up. To change this we will change the SCALE of the second texture.
Click on the green button topleft of texture B (Basic Altitude) to open the Transformation Tools window. Then put your mousearrow on the center of the top cube and drag to the right till you get about 100 %. 
You could also click the values for X, Y and Z separately and enter 100.

Enter this change by closing the Tools window with the check mark.The preview window shows the difference.
   

Why does the scale work like that ? It seems strange that a larger scale should give a smaller transition and a smaller scale should give a larger one.
 The simpler texture on the right shows why : it's mapped here with 25 and 250 % scale.
With a larger scale , the texture pattern gets mapped more times over the same area ; with a lower scale it gets mapped only a few times.
So a lower scale maps out the Basic Altitude over a larger area while the higher scale will map it over a much smaller area. Since it is a pattern that doesn't repeat itself you still get only one transition from dark to light, but now it changes from dark to light over a shorter area.

Ok , so that has pushed the changeover from 'dry' to 'wet' down to where we would like it to be : near the waterline. 
But while we're nearly there , this isn't quite like what the original picture looks like. Dry rock tends to look bleached and it's colours are deeper and more saturated where it gets wet.
The effect we've got now looks more like a rock which is plunged in shadow near the waterline.
With two separate textures , this is the best we can get.

To get a better result ,we will recreate the Altitude effect in a 2nd component in the first texture and combine its 2 components
in another way.

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