2020/2/9 Homework 2
https://shuangz.com/courses/ics162/homework/hw2/index.html 1/4
HW 2: MEL Scripting and Procedural
Terrain Generation
Goal
Introduce you to MEL scripting and experiment with methods for automatic
terrain generation.
In this project you will create a custom tool inside Maya for automatically
generating a terrain.
1. Fire up Maya and open the script editor window. Create a polySphere in
the scene and move it using the manipulator. Observe the commands
which stream by in the History window. Now experiment with copying and
pasting those commands into the script window and executing them. You
can use CTRL+ENTER to execute the commands (or the execute button in
the toolbar at the top of the script window).
2. Look through a couple online tutorials about MEL in order to get an idea
of what a MEL script looks like. I suggest starting with this one: Intro by
Lindsay Grace. While reading this, please use the script editor window to
interactively test out the commands being discussed and see how they
work.
To test your comprehension, try writing a simple procedure which places a
couple spheres in the scene.
global proc drawMySpheres() {
...yourcodegoeshere...
}
Save the script as a text file in the Maya scripts directory as
"drawMySpheres.mel". To run your procedure in the script window, you
can first make Maya load your script by typing "source
drawMySpheres.mel;". This loads your procedure into memory. You can
then run your procedure by executing the line "drawMySpheres();".
At some point you will probably find the need to refer to the
documentation from Autodesk which you can find here: [MEL Command
Reference]. You may also find this wiki a useful reference [MEL wiki].
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One thing to keep in mind when looking online for references for Maya
scripting is that there are at least 3 different ways to interact with Maya:
MEL (which we will use), Python scripting, and C++. Don't confuse yourself
looking at a Python scripting example.
3. Write a MEL procedure named createTerrain which creates a 3D terrain
mesh in the current scene. Since Maya already has procedures for
performing subdivision, we won't need to implement the square-diamond
algorithm described in class. Instead, your procedure should work as
follows:
Create a polyPlane
For some number of specified iterations...
Loop through all the vertices of the mesh and move each one
up/down by a random amount in the range [-d,d]
Subdivide the mesh using the polySmooth command
Decrease the displacement range d by a factor of s
Your procedure should take as input variables the number of iterations,
the initial scale d and the scale factor s.
HINTS:
1. You should be able to implement this script using the following MEL
basic commands and functions:
 polyPlane, for, select, polyEvaluate, rand(), move, polySmooth,
print, if
Look up these commands in the MEL reference as necessary to learn
about their different parameters and flags. In particular, you will want
to experiment with setting the continuity parameter for polySmooth.
2. When calling polyPlane, it is convenient specify a name for the mesh
(e.g. "terrain") so you can refer to it later. However, if the user runs
your script multiple times, the name will conflict with that of the
previous mesh. Maya's solution is to add a number to the end of the
name (e.g. "terrain22") to make it unique. Thus, the best option is that
whenever you create some new object, grab the return value so that
you know the name. In our case, use string $names[] = `polyPlane -n
terrain ....` and then later on when you need to refer to the name
you can use the string stored in the variable $names[0].
3. In your MEL script you will want to perform operations on nodes in the
Maya scene. For example, suppose you have a mesh "terrain" and want
to modify a vertex, whose name will be something like
"terrain.vtx[19]". In your script you will have a string variable $names[0]
which stores the name of the mesh and another integer variable $i
which specifies the vertex number you want to work on. If you try to
2020/2/9 Homework 2
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use $names[0].vtx[$i] you will get an error (why?). Instead you need to
assemble the pieces into a string which is the name of the vertex. For
example:
$myvertexname = $names[0] + ".vtx[" + $i + "]"
4. It is not hard to write a script which causes Maya to freeze up so make
sure and save your script often. In this example, if we subdivide the
mesh too many times, things will grind to a halt. Make sure your
procedure checks the input parameters to see that the number of
levels (iterations) is reasonable (e.g. a max of 5 or 6) to keep this from
happening. Use the error command as appropriate.
4. Make your terrain generator user friendly by creating a GUI. Write a MEL
proceedure called terrainGUI which creates a window with textFields to
enter the terrain parameters and a button labeled "generate" which calls
your createTerrain proceedure with the parameters given in the textFields.
Here is an example script with some commands to get you started:
window -t "TerrainGenerator" -wh 250 250 "MyWindow";
columnLayout;
text -w 175 -al "left" -l "Terrain Parameters";
separator -st "double" -w 200;
textField -text "intialtext" -w 200 "field1";
$whenclicked = "string $f1text = `textField -q -text field1`; print
$f1text";
button -l "print field1" -w 200 -c {$whenclicked};
showWindow "MyWindow";
Note how the button works. When it is clicked, Maya evaluates the string
$whenclicked. In this case we are querying the contents of the text field
(using textField -q) and the printing out the result.
5. Add your terrain generator to the shelf. Once you have your proceedure
saved to a file "terrainGUI.mel", the final step is to add a button to the
Maya user interface. To do this, first enter commands necessary to load up
your code and start your gui in the script window. For example:
source generateTerrain.mel;
source terrainGUI.mel;
terrainGUI();
Now, select the "custom" shelf in the Maya user interface, highlight the
code and drag it to the shelf and indicate that it is a MEL script. This will
create a shelf button that invokes your script any time you need it.
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6. Extend the simple terrain generation function to implement some more
interesting features. Here are three possibilities:
1. Implement plateaus and plains by allowing the user to specify a
maximum and minimum displacement for the terrain map and
modifying your code to enforce these constraints.
2. Implement an option of producing sharp ridges discussed in class by
generating the terrain and then changing the height of each vertex to
be -abs(height).
3. Implement terrain coloring by assigning colors to each vertex using
polyColorPerVertex or by assigning UV-texture coordinates to each
vertex based on the vertex height. If you use the per-vertex coloring
technique, make sure to go to the menu (Color > Toggle Display
Colors) in order to get them displayed in the scene view.
Please implement at least one of these three. You will get up to 10% extra-
credit for implementing all three or some other creative ideas of your own
choosing. To distinguish this version from the basic version you already
implemented, please call your new terrain generator scripts
createTerrain2.mel and terrainGUI2.mel.
Turn In
Turn in a zip file lastname_firstname.zip containing the following:
The MEL scripts you wrote (text files)
A Maya scene file containing a terrain generated by your plugin
(terrain_ex.ma or terrain_ex.mb)
A rendering of a terrain generated by your tool as a jpeg file
(terrain_ex.jpg)