XSI 1.5 Polygon Modeling Tutorial:
written for XSI Illuminated: Foundation
by Anthony Rossano
In this tutorial
you will learn:
o All about basic Polygon modeling
o How to select
polygons, edges, and vertices
o How to sculpt shapes by
o How to duplicate and extrude polygons
o How to Extrude polygons along a curve
to smooth polygonal objects
Our goal in this
tutorial is to use the most basic polygon modeling tools in XSI to
create a beautiful, elegant and simple model, starting from a basic
We'll duplicate polygons, edges, and
vertices, we'll move polygons and components around singly and in
groups, we'll add edges and vertices, and we'll extrude polygons
along a curve. Starting from a polygon mesh sphere we'll quickly
create a very cool jellyfish that we can animate in an interesting
way later on.
We'll focus on sculpting the general shape of the
jellyfish, creating tentacles and contours, without worrying too
much about the finished surface. When we are done we can adjust the
smoothness of the polygon mesh to put the finishing touches on the
Remember polygon modeling is a creative
endeavor. There is no one correct way to do it. If you have ideas of
your own that you want to try, please do experiment and improvise.
If you want to be able to get back to where you were before an
experiment, duplicate your object periodically as you go so you can
always go back to a previous version.
Step 1: Start
with a simple object and then refine it.
- Get a
polygonal mesh sphere and open the geometry property page (immediate
mode must be OFF at this point). We need to have enough detail
around the equator of our jellyfish to pull out little bumps and
nodules, but the sphere currently only has 8 polygons around the
middle, which is not enough.
- We want a pattern of bumps
around our jellyfish like this: little bump, twisted tendril, little
- This pattern will repeat 8 times around the jellyfish
and there are three bumps and tendrils per pattern, so we'll need 8*
3 or 24 subdivisions around the middle of the sphere. Set U to 24 in
the Geometry Property Editor (PE).
- Set the V subdivisions
to 13 so we have enough detail in the sphere, from top to bottom, to
work with. The odd number (13) of subdivisions ensures that one row
of polygons will go perfectly around the equator.
Step 2: Freeze the operator stack before
- Now with the basic Sphere ready to
go, we no longer need to have an operator stack recording each and
every move we make. So, freeze the sphere with the Freeze button and
then turn on the Immediate mode toggle button near the bottom of the
MCP. When Immediate mode is on, each move and tool will be frozen
after it is completed, which will make our job faster and simpler.
We can always turn Immediate mode back off at any time.
Make the Bell shape of the jellyfish.
three rows of polygons at the equator of the sphere using the
polygon Select By Rectangle hotkey, which is Y. Now scale the three
rows in Global Y to make them half as tall as they were. These will
become the lip of the Jellyfish, and we want more fine detail here
so we made the rows smaller.
- Deselect the rows using the Y
hotkey and the Middle mouse button so that you don't accidentally
transform these polygons by mistake later on.
- Now, tag
all the points in the lower half of the jellyfish (not including the
points around the very middle) and scale them in Object mode Y to
completely invert the lower half inside the upper half. Object mode
means that the points will scale relative to the center of the
- Gently scale these same points in X and Z
(hold down the left and right mouse buttons at the same time) to
make the inside membrane slightly smaller inside the outer shell.
Stop when the top row of tagged points is even with the bottom of
the equator and untag just that top row, and then keep going. Untag
all the points (T and the middle mouse button) when you are done
turning the sphere inside out to form the jellyfish.
4: Add some detail to the top of the jellyfish.
The top of a jellyfish has areas that are thicker, arranged in a
star shape radiating from the center. On our Jellyfish we can do the
same thing by selecting some polygons in a pattern and duplicating
them, then raising them up and out just a little bit. Using the
polygon Select by Raycast hotkey U, select a stripe of four
polygons, starting with the second from the top and extending down
almost to the equator.
- Our jellyfish will have six of these
bumps, so repeat this pattern every fourth column. Refer to the
Figure to get some ideas about neat patterns for this, and
experiment with your own.
- With these patterned polygons
around the top half of the jellyfish bell selected, extrude them
with the Extrude Polygon on Axis hotkey, which is CTRL-D. This
created new polygons, which lay exactly on top of the other ones.
- We need to move these new polygons a little bit. Activate
the transform area of the MCP, and make sure that you are in Local
transformation mode. When in local mode, each group of polygons will
move according to its own axes, which is often useful.
Now, translate the selected polygons only in Y, which will move the
polygons up and out from the center just a little ways. You may also
scale these polygons down in X and Z slightly, also in local mode.
- We've just created
contours like a topographical map. Don't worry about how blocky it
looks now, this will become smooth later. Deselect all the polygons
since we are done with them now.
Step 5: Pull out
the underside of the jellyfish.
- Using your best
artistic judgement, select some polygons in the middle of the
underside of the jellyfish and translate them in global Y to add
more mass to the middle of the jellyfish.
- Deselect those
polygons, and then tag the point in the absolute middle of the
bottom of the jellyfish. Translate the tagged point down in global Y
just a bit. We want the middle of the bottom of the Jellyfish to
drop down a ways more but we need more detail. When you extrude a
tagged point, new edges and polygons are created which would give us
- Extrude the tagged point with the CTRL-D
hotkey. Now move the selected center point down a little more,
repeat the CTRL-D again, and move it down some more. Untag that
point when done.
Step 6: Add some
more shape to the bottom.
- We could add more
detail to the polygons surrounding the bottom point we just pulled
out to create some ridges that would look interesting. Look at the
edges just connected to the center point that we pulled in the step
above, and select every fourth one with the Select Edge By Raycast
tool, hotkey I.
- When all six edges are selected, extrude
these edges just like we extruded the points and the polygons, with
CTRL-D. New edges, new points and new polygons will be created.
Translate these new edges in local Y to make them move out from the
center just a little ways.
Step 7: Add some
small bumps and tendrils.
- On the underside of the
rim of the jellyfish, there are 24 polygons. We can use these to
create small bumps and tendrils in the pattern bump-bump-tendril
repeating around the rim.
- Select every third polygon and
extrude it with CTRL-D, then translate it in local Y a little ways
from the lip and scale it down a bit in local X and Z. This will
make a small bump there when finally smoothed.
these polygons, and select every third polygon next over along the
rim. Repeat the extruding and scaling process, but make these bumps
a different length and size.
- Deselect those
polygons, and select the remaining 8 polygons of the lip. These we
will extrude in a different way to make more interesting tendrils.
- We want to adjust the
properties of the tendrils after we execute the command, which would
not be possible in Immediate mode, so turn off Immediate mode. This
means that when we do our extrusion we'll get a Property page for it
where we can make changes (or even animate them).
Immediate mode off, execute the PolyMesh]Extrude Along Axis command
in the Modify]Poly Mesh menu. You can also get this command by
holding down the Alt key (or CTRL-ALT on Irix) on your keyboard and
left clicking. Left-click over one of the selected
- The polygons will be extruded slightly, but we
want to do much more. Select the jellyfish as an object (with the
spacebar) and search in the Selection button of the MCP to find the
Extrude Op. Open it by clicking on the icon. In the Extrusion Op
Property Editor (PE), make sure that the Frame toggle is on, which
will transform each polygon relative to its own local axis and be
easier to control and more interesting.
- Next, adjust the
extrusion Length slider to about 4, and increase the number of
subdivisions to 7 to make the tendril more detailed. In the
Transform tab of the PE, you can adjust how each subdivision of the
extrusion is scaled, translated or rotated. Adjust the Rotate in Y
to about 15 degrees, and make the scale in X and Z about .80, which
means that each new segment in the extrusion will be 80% as big as
the prior one. As you make these changes you can see the tendril
grow and change.
- Make sure you close the PE and deselect
the polygons at the ends of the tendrils before you move on. Now we
have nice bumps and tendrils around the rim of the
Step 8: Make four
- Our jellyfish needs four
larger, longer tentacles that will trail behind, contracting and
expanding as the creature swims. These need to be animated
eventually. The clever way to do this is to extrude some polygons
from the base of the creature along a curve. Then the extrusion
itself can be animated and the curve shape can be animated.
- Examine the underside of your Jellyfish (is it a boy or a
girl?), and select four polygons (every sixth in a circle) somewhere
near the middle of the underside.
- We want these polygons to
be quite flat in the XZ plane, so they extrude straight down. Make
them flat by scaling them in OBJECT Y, then scale them slightly
larger using Local X and Z, and translate them down a ways so they
become good foundations for the tentacles.
- Using the CV NURBS
Curve tool, draw a serpentine curve in the Front view, starting at
the global center with about 6 control points. This will become the
shape of the tentacles.
- Select the jellyfish again with
the spacebar, and activate the selected polygons by tapping the U
hot key or by clicking on the Polygon filter button in the MCP.
- Choose the Poly Mesh]Extrude Along Curve tool, and then
pick on the curve to finish the command. Again, select the jellyfish
as an object or enter Object mode, open the Extrude PE (there will
be two now we want the top one) and check that autorotate is
off and perpendicular is on.
- Increase the number of
subdivisions to 12, to make for a smoother tentacle, and again
adjust the scale of each subdivision in the transform tab to perhaps
0.9 in Scale X and Scale Z, with a small rotation in Y for
- Try out the End slider to see that
this makes the tentacles extend and contract. You could animate this
later as the creature swims.
OK we are done with the
Smoothing the surface
- Select the jellyfish as an
object, and in the Selection button find the Geometry Approximation
PE and open it up. By default, the Geo approximation property is
shared with all objects and we want one specifically for the
Jellyfish, so in the dialog choose to create a local copy.
In the Polygon Mesh tab, increase the Mesh Subdivision to 2 and then
examine your jellyfish in the shaded view and the render
Looks good! Apply a cool translucent material, then
save the Jellyfish so we can animate it later.