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Materials Plugins
The Worley (v2.0)
Click here to download
it (for A:M v8.5, Windows).
Copy the trb into your A:M turbulence folder.
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The Worley
Plugin is based on the work of Steven Worley who published an article
in the SIGGRAPH 96 proceedings titled "A Cellular Texture Basis
Function".
The plugin is essentially the same algorithm as the CellTurb
plugin but with all the properties discussed by Worley exposed
to the user and with some more properties I added.
I invite you to take a look at a slide
show type of presentation about the paper with nice pictures
by Michael Monks.
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| Also
take a look at my old Worley plugin page
for more texture examples done with the plugin.
The basic idea of the function is to compute the distance from
any render point on the surface of the object to some cell centers.
In other words, you have a bunch of cells inside the 3D space.
We know the location of each cells in the 3D space and each time
we need to render a point on a surface, we take the XYZ coordinate
of this point and compute the distance to the center of each of
those cells and return the shortest distance we found. Of course,
we don't compute the distance to all the cells. That would take
infinite time. We use space partitioning tricks to limit the number
of cells to look at.
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| If
you want to have an idea of those cell, create a Worley material
and set its scale to 500, the first attribute to white and the second
to black. On the worley tab, check the "Rooted" and the
"Inverse Distance" checkboxes and set the "Bias"
to -25, the "Gain" to 127 and render. |
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In the material examples I show below, the material scale is
set to 500, the first attribute is white and the second attribute
is black.
Worley tab
Distance
There are 4 distance functions Euclidian, Manhattan, Camberra
and Minkovsky. My goal here is not to give mathematical description
of those distances.
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Euclidian |
Manhattan |
Camberra |
Minkovsky |
Euclidian
The Euclidian distance computes the real straight line distance
between two points. It produces round cells
Manhattan
The Manhattan distance computes the distance by adding the X,
Y and Z distances. It is called Manhattan because of the similarity
of having to walk around blocks in streets when you want to go
from one point to another in a city. It produces diamond cells
Camberra
The Camberra distance is a statistical distance. It is not well
implemented in my plugin but I haven't found a suitable implementation
because it is too dependent on the origin coordinates. I shall
rework it eventually or remove it. The reason it is there is because
I haven't decided what to do with it yet.
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Minkovsky
The Minkovsky distance is a exponent controllable distance function.
When Exponent =1 you get the same result as Manhatan and when
Exponent=2, you get the same result as Euclidian. As you go below
1, it produces stars cells and as you go higher than 2, it produces
squarer cells.
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Exponent = 5 (rooted) |
Rooted
Rooted tells the distance function to compute the root of the
otherwise unrooted computed distance. This is to accelerate the
computation and comparison of distances. Normally, the distances
are rooted but some different effects are achievable without rooting
the output. Root is only applied to Euclidian and Minkovsky.
Inverse distance
Inverse distance inverses the value returned by the function.
What should be 0 becomes 1 and vice-versa.
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Plated
Plated assigns a constant value to each cell. It can be used
with all distance functions.
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C1, C2, C3, C4
Those are Worley constants. To understand them it is better to
set the distance to Euclidian and Rooted.
C1, C2, C3 and C4 are respectively the distance from the render
point to the nearest cell, to the second nearest cell, to the
third nearest cell and to the fourth nearest cell.
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C1=1
C2, C3, C4 = 0 |
C2=1
C1, C3, C4 = 0 |
C3=1
C1, C2, C4 = 0 |
C4=1
C1, C2, C3 = 0 |
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Those constants are multipliers which mean that any distance where
the multiplier is 0 is not taken into account in the output. when
a multiplier is 1, the corresponding distance is added once to the
result and when a multiplier is -1, it is subtracted once to the
result. So you could add together 1/2 the distance to the nearest
cell and 1/2 the distance to the next nearest cell by setting C1=0.5
and C2=0.5.
But things starts to be interesting when you subtract the nearest
distance from the next nearest distance by setting C1=-1 and C2=1.
This setting is the basic setting for flagstone type of material.
You will discover nice textures by experimenting with adding and
subtracting cell distances.
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C1= 1, C2 = -1 |
C1= 1.5, C2 = -1 |
C1= 1, C2 = -2 |
C1 = 1, C2 = -1,
C3 = 1, C4 = -1 |
Gain
Gain is used to amplify the values output by the function. It
may be used in conjunction with the ">>" button
which displays the current minimum and maximum values output by
the function.
One of the use of the Gain property is to get the most out of
the output. For instance, if you take the basic flagstone material
with C1=-1 and C2=1, and click the >> button, you will see
that the valued output by the function are from 0 to 55.5 while
the optimal range of values would be from 0 to 100. You can increase
the range of values by increasing the Gain. For instance with
a Gain of 180, you get range of values from 0 to 99.8.
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Another use of this property is to amplify the output in order to
exaggerate some attributes. For instance, if you enter a Gain of
5000, you get a more convincing flagstone texture. However, the
lines separating the stones are too thin. |
C1 = 1, C2 = -1,
Gain = 180 |
C1 = 1, C2 = -1,
Gain = 5000 |
Bias
We may enlarge those lines by shifting the function in the negative
range and we do that by entering a negative value in the Bias
property. For instance, entering -200 in the Bias will enlarge
the space between the stones. However, because the negative values
goes well under 0, the lines are not black.
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C1 = 1, C2 = -1,
Gain = 5000,
Bias = -200 |
Use Limiter
A function output value of -100 have the same effect as an output
value of 100. More generally, negative values have the same effect
on the attribute mixing as positive values. This is why the lines
between the stones are not black. The "Use limiter"
will bring all negative values to 0. So if you check the "Use
Limiter", the lines between the stones will fill in black.
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C1 = 1, C2 = -1,
Gain = 5000,
Bias = -200
Use Limiter |
Multiplier
This property does not do what it was intended to do yet. I shall
work on it later.
>>
The >> button displays the range of values actually produced
by the function. Note that you will get better estimates if the
Material preview window is opened when you change the combiner
properties or after you have quick-rendered your object or group.
Otherwise, the samples are taken from the tiny square in the material
tree.
Distr + Turb tab
Distribution
For those familiar with statistics and a normal distribution,
you will get the idea right away. For all the others, those properties
controls the distribution of cells in the 3D space. The default
values of 5 and 5 means that there are a mean of 5 cells in each
1cm cube of space but he number can vary somewhat from 1 up to
about 10 but still 5 most of the time.
Mean
Mean controls the average number of cells per cm3.
Var
Var controls the variation in the number of cells. For instance,
if you where to enter a Variance of 0.01, you would be almost
assured that almost all 1cm cube of space will be filled with
5 cells thus producing a much more uniform distribution of cells.
Conversely, if you enter a Variance of 20, you would have a wide
variation in the number of cells in each cm cube of space including
possibly no cell at all producing a very non uniform cell distribution.
Octave, Lacunarity and Dimension
I am not satisfied with the Fractal combination of the Cells
Layers yet. As it is now, it may be useful for some applications
but I don't guarantee that future versions of the plugin will
combine the layers in the same way although I might probably add
a v2 compatibility checkbox.
I refer you to my Octave
description page for those properties. As a note, don't forget
to adjust both Bias and Gain when playing with those settings.
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Perturbation
When you look at the basic Flagstone texture, even though we
increased the gain and lowered the bias, those straight lines
are still not that convincing. We can add perturbation in those
straight lines through those properties.
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Scale = 40,
Amplitude = 5 |
Scale = 40,
Amplitude = 5
+ Scale = 4,
Amplitude = 0.5 |
Scale
Scales the perturbation, Larger scale will produce whide perturbations
while smaller scales wii produce small ripples.
Amplitude
Increase or decrease the amount of perturbation on the texture.
Large amplitude can give wild texture effects.
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© Yves
Poissant, 2002 |
