Displacement Mapping
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In this tutorial we'll examine displacement mapping in V-Ray. We will
concentrate on the 3d displacement mapping method.
What is displacement mapping?
Displacement mapping is a technique for adding geometric detail to
surfaces at render time. In contrast with bump mapping, which works by just
changing the surface normal to create the illusion of surface detail,
displacement mapping modifies the surface itself. Here is an example of the
same object rendered with bump mapping and with displacement mapping:
In the case of displacement mapping, the surface is actually modified,
which leads to correct outline, shadow and GI. In the case of bump mapping,
although the surface appears modified, the outline and the shadow stay the
same.
Note that displacement is different from other kinds of shading, since it
needs to modify the actual object surface. Therefore an object must be
displaced before it can be rendered. This is why in V-Ray displacement is
represented with a modifier (although the modifier can take the displacement
map from the object material).
A simple example - a displaced sphere
Start with an empty scene. Create a GeoSphere with a radius about 40
units in the viewport and choose V-Ray as the renderer. Apply some Standard
material to the sphere.
Applying the VRayDisplacementMod
Go to the Modify panel and apply a VRayDisplacementMod to the sphere. If
you render straight away, you will notice a slight displacement effect, like
so:
This is because V-Ray applies a simple noise displacement map when no
other texture is chosen.
Selecting a displacement map
To select another map, click the texture button in VRayDisplacementMod.
This will bring up the Material/map browser dialog. Choose a Cellular
texture. To edit the newly created map, open the Material Editor and drag
the map from the button in VRayDisplacementMod to a slot in the Material
Editor. Choose the Instance method when you drop the map.
If you render again, you should get a similar result:
Setting the displacement amount and shift
To make the displacement effect more pronounced, increase the
Amount value of VRayDisplacementMod. If you
set it to 5.0 and render you will get something
like this:
The Amount value determines the maximum
displacement amount (which occurs at places where the displacement map is
white).
You can shift the whole displacement map up and down by adjusting the
Shift parameter. The effect will be to expand
(for positive Shift values) or shrink (for
negative Shift values) the displaced surface.
Here are some examples of different Shift
values:
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Shift = -5.0
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Shift = 0.0
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Shift = 5.0
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Note that the Shift parameter is an
absolute value in world units. If you change the
Amount, you will probably need to adjust the
Shift too.
Clipping geometry using the Water level
The Use water level and
Water level parameters allow you to clip
parts of the object. Return the Shift value
to 0.0, if you have changed it. Then turn on the
Use water level option and set the
Water level to 2.5:
The geometry is clipped away for those places in the displacement map
where the displacement value is below the Water
level. Here are a few examples of different
Water levels (assuming the Amount
parameter is still 5.0 and the
Shift parameter is 0.0):
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Water level =
0.0 (no clipping)
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Water level =
1.25
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Water level =
2.5
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Water level =
3.75
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Water level =
5.0 (all geometry is clipped)
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The Water level parameter is also absolute
in world units. If you change the Amount
and/or Shift, you will probably need to
adjust the Water level to get the same
effect.
For 3d displacement, the geometry is clipped on a sub-triangle basis - a
subtriangle is either clipped away entirely, or completely visible (this is
not the case for 2d displacement where clipping is more precise). Therefore,
you may get a jagged effect at the clipped edges. You can reduce this effect
by producing more subtriangles (see the next section).
Displacement quality
V-Ray does 3d displacement by subdividing each triangle of the original
object into a number of subtriangles. More subtriangles mean better
displacement, but will also take more memory and will increase the render
time. To get a better idea of how many subtriangles you have, apply a
Standard material to the sphere (if you haven't done so already) and turn
its
Faceted option
on.
This is important, as otherwise V-Ray will not only smooth the surface
normals, but will also automatically apply a normals map that represents the
normal of the perfect displaced surface, which will make the surface look a
lot more detailed that it actually is. Also, switch
off
the
Use water level option of
VRayDisplacementMod, if it is on. If you render, you should get a similar
result (click the image for a larger view):
Here is a blow-up of this rendering to better show the individual
subtriangles (click the image for a larger view):
In addition, here is a rendering that shows the boundaries of the
original triangles of the sphere. To do that, put a VRayEdgesTex map in the
Diffuse slot of the material and instance this map into the
Self-illumination slot. Set the
Color of the
edges in the VRayEdgesTex to red and the
Thickness
to
World units:
The quality of the displacement is determined by the size and number of
the subtriangles. The main parameter to tweak is the
Edge length. It determines the maximum length of a subtriangle's
edge. This can be in world units or in pixels, depending on the
View-dependent option. Lower values for
Edge length mean smaller triangles and better
quality. Here is the previous image rendered with various values for
Edge length (with
View-dependent turned
on). Note that the
View-dependent option refers to pixels in the
original image, not the zoomed-in image you get with a blow-up rendering.
This is why we were able to do a blow-up rendering to see the individual
subtriangles better. Click the images for a larger view:
Edge length
value
0.5 |
Normal rendering |
| |
Blowup rendering |
Edge length
value
1.0 |
Normal rendering |
| |
Blowup rendering |
Edge length
value
2.0 |
Normal rendering |
| |
Blowup rendering |
Edge length
value
5.0 |
Normal rendering |
| |
Blowup rendering |
Edge length
value
10.0 |
Normal rendering |
| |
Blowup rendering |
