XSI Foundation 1
XSI Foundation 1.5
XSI Character Animation
Maya Games
XSI 1.5 Polygon Modeling Tutorial: Jellyfish
written for XSI Illuminated: Foundation 1.5
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 transforming components
o How to duplicate and extrude polygons and vertices
o How to Extrude polygons along a curve
o How 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 polygonal primitive.
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 jellyfish.
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 bump.

- 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 continuing.

- 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.

Step 3: Make the Bell shape of the jellyfish.

- Select 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 sphere object.

- 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.

Step 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 more detail.

- 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.

- Deselect 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).

- With 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 polygons.

- 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 jellyfish.

Step 8: Make four larger tentacles.

- 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 additional interest.

- 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 polygon modeling!

Step 9: 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 region.

Looks good! Apply a cool translucent material, then save the Jellyfish so we can animate it later.