User manual

© Next Limit Technologies 2010
Maxwell Render 2.5 User Manual
Chapter 10. Maxwell Materials | 78
on the BSDF component > Add Coating, and then simply hide the BSDF clicking in the
visibility column in the layer list to disable it.
10.06 Displacement
Contrary to bump/ normal maps, the displacement feature simulates real geometry at
render time as if it was actually modeled. This feature is very useful for adding ne detail
to a mesh which would otherwise be difcult or impossible to actually model. Displacement
uses a texture to dene the geometric detail. Unlike many other displacement solutions
which pre-tessellate the geometry, causing an increase in memory usage at render
time, often of hundreds of megabytes for large detailed displacement, Maxwell’s unique
displacement method allows you to create virtually unlimited detail while using very little
extra memory.
A displacement component can be added to the material (only one component per layer
is allowed) by right-clicking in the Layers list area of the Material editor, or from the Edit
menu of the Material Editor. Please note that, although you can have several displacement
components in a material, only one of them will be selected for rendering. You can specify
which one you would like to use by clicking on the Material Properties row in the Layers
list.
To use displacement, you need an object with UVs, and a displacement texture. The
texture is similar to a usual grayscale bump map, with different shades of gray to describe
elevation levels. Lighter grays will raise the geometry and darker grays will create cavities.
Displacement Map
You must rst load a displacement texture to access the displacement parameters. Maxwell
Render can use 8, 16 or 32-bit grayscale displacement maps. It is recommended to use at
least a 16-bit displacement image to create a smooth displacement, because 8-bit images
may not contain enough gray levels (they only contain 256). You may see a stair-stepping
effect if using 8-bit maps. 8-bit maps may be enough for displacements that do not
require smooth transitions between gray levels, and additionally Maxwell Render’s texture
interpolation helps to render even 8-bit images smoothly.
Height
This parameter sets the maximum distance displaced. It tells the engine how much real
geometric height you want to displace on your base mesh. This value needs to be greater
or less than zero for displacement to appear. The white of your texture will be raised to the
height value you set. Displacement height can be set in percentages or in absolute units:
• Percentage (%): Set the desired height as a percentage of the longest edge of
the associated object’s bounding box. For example, if you have a car of 300 x 150 x
110 cm and you set height as 1, this means the peak displacement will be 1% of 300
(the longest edge of the bounding box) which is 3 cm to be observed as real length
in render output. Using relative height is useful when you wish to preserve the same
displacement height when scaling the object.
• Centimeters (cm): Set the height in centimeters to always displace to this given
value regardless of object dimensions.
Offset
This parameter allows you to specify which gray level in the texture should represent zero
displacement. It is important that you set this parameter correctly, based on what type
of displacement map you use. For example, some displacement maps may use 50% gray
as zero displacement (darker shades than 50% in the texture will create cavities, lighter
than 50% will raise the geometry). In this case, you should set the Offset parameter to
0.5 to get a proper displacement. If your displacement map uses black to represent zero
displacement, set Offset to 0.
Gain
Gain denes surface accuracy, ability and response to detail, independent of texture
resolution. It is a measure of the subdivision level of the mesh: the higher the Gain value,
the more accurate the result, but also the more subdivision of the mesh during render
time, meaning longer render times.
Gain and texture resolution are strongly related:
• When specifying a low Gain value and using a high resolution texture with lots of
detail, the nal image will not show more detail than what is allowed by the Gain
value.
• When specifying a high gain value but using a low resolution texture, the image will
reach the limit of the pixel detail of the texture and will not show a more detailed
displacement. The displacement will reach the detail level of the texture. This is
important to understand because you can optimize the displacement by starting with
a high resolution texture and lower gain value, and keep raising the Gain value until
the detail in the displacement is satisfactory.