3.0 Running the Plugin
3.1 The Data File and its Parameters
In the data file, "***" marks a comment, i.e. ***This is a comment***
The sequence of the different parameters does not matter. What is important
is that the key word at the beginning of the line is followed by a = ,
then the value, then a period, which terminates this data. i.e. KEYWORD=VALUE.
An example of data.txt
A list of data.txt parameters and possible values:
| GENERAL PARAMETERS |
| FILTER=0. |
Filter is toggled on/off with 0/1 |
| THRESHHOLD=10. |
Threshold is the distance for points to be filtered |
| SHARED=4. |
shared is the no of points on the same vertex for filter3 |
| FILTER2=0. |
filter2 toggled on/off with 0/1 |
| FILTER3=0. |
filter3 toggled on/off with 0/1 |
| FACET_SIZE=4. |
number of points which form a surface (grammar rule
S or T) |
| MESH=0. |
toggles the creation of a mesh on/off with 0/1 |
| TREE=0. |
toggles the generation of a fractal tree on
or off 0/1 |
| GENERATION LIMIT=10. |
sets the number of generation for the L-System (not the tree) |
| CHILDREN SPAWNED FOR TREE MODE=4. |
sets number of branches for the tree mode |
ANGLES / 10 (275 means 27,5 degrees).
The syntax for numbers is to leave out the comma. |
| ALPHAA=300. |
the angle for turning left or right
of the turtle |
| BETA=300. |
the angle for rolling left or right of the turtle |
| GAMMA=300. |
the angle for pitching up or down of the turtle |
BOUNDING BOX VALUES / 10 (44 means
4,4).
The bounding box limits the growth of the L-system to a box |
| X1=-120. |
starting one corner specified with X1 Y1 Z1 |
| Y1=-100. |
|
| Z1=-100. |
|
| X2=120. |
and the other corner diagonally across from
the first |
| Y2=100. |
|
| Z2=300. |
|
| |
|
| SX0=0. |
the starting point of the growth is specified
in SX |
| SY0=0. |
for multiple surfaces SX is incremented by one for |
| SZ0=0. |
each additional system SX0 ... SX1 ... |
***GRAMMARS***.
The Grammar specifies the actual growth |
| X=f&&&fK. |
the axiom is read in and executed replacing each
letter |
| K=Yf[>>>f<<<fY] [<<<f<<<fY]K. |
with its rule if there is one specified |
| Y=F[^^^F]>>>F[^^^]Y. |
[]safe and restore the state of the system (for branching) |
| S=f>>>f>>>f>>>f. |
S and T are reserved for surfaces and are unaffected
by affectors and repellers |
| ***REPELLERS/ATTRACTORS***. |
| R0-X=0. |
R stands for attractor and repellers. R is incremented |
| R0-Y=-10. |
by one for each new attractor and repeller
R0 .. R1. Its |
| R0-Z=10. |
power being positive or negative determines whether it is |
| R0-POWER=0. |
an attractor or an repeller. (pos attracts
neg repels) |
| R1-X=-100. |
XYZ sets its position and the power the zone of influence |
| R1-Y=-30. |
on the growth |
| R1-Z=35. |
|
| R1-POWER=0. |
|
3.2 The Grammar
The syntax of the grammar consists of the following symbols:
| X,
W, Y, K |
are letters for which rules can
be defined. The first Letter defined is the axiom that is read in
by the interpreter |
| <> |
turns the turtles orientation left/right with the
angle specified in alpha multiple signs have an accumulative effect
> = 30,>> = 60, > = 0 degrees for alpha=30 (in data.txt
30 degrees would be written 300) |
| - + |
rolls the turtle along its length
axis at an angle specified in Gamma. accumulative in the same manner
as <> |
| ^& |
pitches the orientation of the turtle ^ up and down
& at the angle specified in BETA accumulative in the same manner
as <>. |
| f |
moves the turtle on unit forward in its current
orientation. With the forward movement the direction of movement
becomes the new local orientation of the turtle (what was up from
its former state now is forward) this takes only affect after f
or F have been called. (so >^f is not the same as >f^) |
| F |
is the same as f only it draws a line for its path
of movement. |
[
] |
pops a state on the stack. Meaning
the current orientation of the turtle is stored ] and with this
sign returned. This means f[<f]f moves forward saves the position
and orientation it is at turns right and goes forward and then returns
to the saved position and orientation going forward one step in
the initial direction this causes a branching to take place |
| S |
in this grammar reserved for the creation of a surface
polygon of n vertices, where n is defined in facet_sides in the
data.txt file. The interpreter will attempt to create a closed polygon
out of the moves defined here using small f (a triangle with alpha
at 30 would for instance be f>>>>f>>>>f
forward turn 120 degrees to the right move forward turn right 120
move forward. The number of f's have to match the facet_number otherwise
nothing will be drawn. That means the starting does not have to
be reached again) |
| T |
same is true for T as for S. |
3.3 The Filters
Through the development of the plugin there have been several
stages in trying to optimize the interplay of L-system grammar and attractors
and repellers with a usable outcome. As always, it is difficult to exactly
specify what is usable and what is not, therefore there are different
not necessarily coherent implementations of experimental nature in this
plugin.
The main problem comes from the distortion of the geometry specified
in the grammar. Due to the effects of the attractors and repellers, surface elements which
should form a closed surface in the grammar become disjoint.
The three filters try to solve this problem with different approaches aiming at closed surface
displacing the surface vertices to match their neighbours.
First Implementation "filter"
Filter parses the set of surface vertices after their initial grammar
generation and joins them within a certain radius of each
other, as specified in the threshold parameter. If there are more than three
vertices, the filter tends to leave gaps. The advantage of filter is that
it works with all grammars since it is not dependent on the number of surface
vertices. It also joins any surfaces close together which causes surfaces
from different lines of growth to be stitched together.
Second Implementation "filter2"
It is an optimization of the principle of the first filter, specific for
the use of hexagonal grammars. It averages the three closest vertices
into one point thereby closing gaps. If the distance is too big, the
gap stays open.
Third Implementation "filter3"
The third filter is based on the idea of using the links which derive
from the non-deformed grammar as the pattern for joining the surfaces
after the attractor and repellers effect. Therefor it is guaranteed that
a grammar that forms a continues surface in an undisturbed run will form
a continues surface in the disturbed run as well, making the outcome more
predictable.
The filters are to be used one at a time (not in parallel) or switched
off completely
3.4 The Surface Option
The filters in combination with the L-system and an appropriate
grammar form a surface. The plugin still has a secondary function which
is the
3.5 The Tree Option
if the tree option in data.txt is toggled on it produces
a fractal tree using the child_node for determining how many branchoff
are generated at each joint.
3.6 Examples of Grammar Inputs
a hexagonal grammar based on alpha=300 beta=300 gamma 300
it generates a continues honeycomb-like surface growing from a point with
the parameter
filter3= 1
facet_nodes=6
shared=3
Grammar:
X=f&&&f>>>>>>f[K]>>[fK]>>[K]>>[fK]>>[K]>>[fK].
K=Y>>f<<fK.
Y=S<<f>>fY.
S=<<f>>f>>f>>f>>f>>f.
a continues rectangular grid example
filter3= 1
facet_nodes=4
shared=4
Grammar:
X=&fK>K>K>K.
K=Y>f<K.
Y=SfY.
S=f>f>f>f.
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