Basic Splinemanship V5 - V8.5 (Revised 2/20/02)

A Simple Tutorial About Working With Hash Splines
V9 has changed the extrude function which is not covered in this tutorial.

©1999 By Jeff Cantin aka TinCan on IRC

A Quick Look to Get Started

Fig. 1

 

 

Let's take a looky at what we have in Fig. 1.
A = a 2 point spline
B = a 3 point spline
C = A & B joined
D = closed 4 point spline
E = two splines not joined
F = E's two splines joined
G = F with the tails moved

I am going to go real slow and be as detailed as I can, some may find this condescending (sorry), but I want to help you learn--not confuse you. OK? OK! And I recommend you open any version of Hash's 3D modeler and follow along. You may find it helpful to print this out, and then follow along.

Figure 1.

Now for more details, Fig. 1 is a direct screen grab in the "shaded mode with wireframe"
and I only added the red letters in Photoshop. The light blue color shows that a valid patch
was created and will render. I adjusted the CP (Control Point) size to be larger in the
"Tools -- Customize" drop down menu, so your screen may look a little different.

First definition:Valid 4 Point Patch = Any closed combination of
4 CPs on two or more splines.

"D" Lets examine "D" and using our definition we see why "D" did not render (turn blue), all the CPs are on the same spline.
"E" "E" did not render (turn blue) because they are not connected yet, so, they don't make a closed combination of CPs and splines.

F and G

Finally, "F" and "G" are exactly the same. (HUH? Funny they don't look the same.)
Here's why – I left the "tails" (painted yellow) on the two splines to show you how
splines work. I dragged the "tails" to different places to demonstrate the following
point. A spline passes through a CP and tries to go from one CP to the next as
smoothly as it can
, more on this later. Let's learn to join splines into rendering patches
so you can make your own!

Joining Splines in 3D Space

Let us continue, with this assumption in mind, I will name the tool used as it is
displayed when you have your cursor over it, i.e. the little arrow Button with the
plus sign = Add Mode (A) Button, where the (A) is the keyboard shortcut key.
Using this button make two splines similar to fig. 1's "A" and "B" yes... I know
"B" has three CPs, we will add a new CP to "B" in a moment. You should notice
that the tool buttons are context sensitive and only become active if you can use
them for an operation. While you have a CP selected on the "B" spline, whack the
"Insert (Y) Button" "Add Button" --there, you have just added a new CP to spline "B"! Move
that CP around a bit and you will see what I meant earlier about splines wanting
to stay smoothly curved.

"a and b"

Position the new CP to match spline "B."

Joining "A" and "B" together
Grab the end of spline "A" and position it "over" the center CP in spline "B."
Don't let go yet! On a PC, while still holding the CP with the left mouse button,
right click with the mouse and the two CP's will weld together. On a Mac, while
still holding the CP with your only *smirk* mouse button whack the "~" (tilde key)
and the two splines are joined. Now drag that CP around and watch the splines move.

Here is a helpful rule to remember:
The CP you are "holding/moving" will move in 3D space to the CP you
are "holding" it over
. This fact is very important, and important to learn early!
You're moving the CP to weld it to a stationary position.

Make the "A" and "B" splines again on a different part of the screen, this time for
spline "B" you can use the "Add Lock Mode (shift +A) Button" and directly draw
a spline with 3 CPs on it. Now, grab the center CP on spline "B" and move and
weld it to the end of spline "A." Notice the difference in the resulting shape. I'm
not showing a picture here so that you have to look on your own screen. Pretty
tricky huh.... ;-)

If you actually followed along using your Hash modeler, I should mention that we
were working in only two dimensions, X and Y. To see this for yourself, change your
model window to any other view. See, no depth, no Z... To continue testing the "rule"
I underlined above, go back to the view you started in and use one of the group tool
buttons to select one set of joined splines. While the group is still selected, change the
view to right, and from the keyboard press the "left cursor arrow key" several times to
move the selected splines away from the starting place, I want you to move them
fairly far apart from each other. Good!

Now go back to the view window you drew them in. Whoa! it looks like nothing
happened! That's because there is no depth cue in wireframe mode! Grab a CP,
any one will do and try the same welding technique we just learned. Change views again
and study the results... repeat connecting different CPs and looking at the results, untill you
get that little lightbulb over your head and totally understand which CP moves when
you make a weld! I know you want to make kewl models, but if you don't get this
part in your head early I can pretty much tell ya you will have problems later.

Take a break and look at some of my pretty pictures! My Hobby Page

Ok, are you ready to continue? Good! Now that you can connect (join, weld) CPs together,
and you know which one to grab and that it will move to the other, lets continue with basic
splinemanship. Of course, everyone wants to make stuff that's going to render, so that's our
new goal! There are four classes of patches (IMHO), they are: 4 point patch (the best type),
3 point patch (will render, but may cause unwanted render artifacts), a patch made with
a hook, and with Version 6 and above, you can make a 5 point rendering patch using the
5-point patch button. I gave you a good working definition earlier of a 4 point patch, and that's
what we will make and use in our examples.

Let's make a patch...

Fig. 2

Figure 2.

Draw a spline with the Add Mode (A) tool, as in Fig. 2. Select the entire spline. There are two
ways to do this, draw a bounding box around the spline, or, select any CP and press the "/" (Slash Key).
The "/" key will select all CPs that are connected to the spline(s) or mesh. On your own, open the
Diane sample model and select any CP and try it! Diane is not a unibody model, her legs are not connected
to her body, nor is her hat. By using the "/" key you can examine how others put models together.
OK! Back to our lesson! LOL...

This is what I mean about "splinemanship," how they work and what tools you have available. Back to
our two point spline! Now that it is selected, position your cursor inside the yellow bounding box.
PC folks right click, Mac folks command click, and you will get a new menu, select "snap to grid" and
the CPs will jump to the closest grid point. We really didn't have to do this, I just wanted you to know
"snap to grid" was there, sometimes you may find snapping to grid helpful (for cubes & stuff). The same
thing is true for this next step, it is just to demonstrate the tool exists... The 2 point spline is still selected,
if it's not, then select it again, on the top tool boxes select the "Snap Manipulator to Grid" button and then
select the "Extrude (E)" button.Now, drag the still highlited spline down as shown in Fig. 2. You should
notice the extrusion jumps from grid to grid, turn off the "Snap Manipulator to Grid" and move the spline
around some more. Again, we really didn't need to use this tool, but now you know what it does! You
could right click again and snap this spline to the grid points so you end up with the example in Fig. 2. Click
on a render button and the patch will render.

Let's examine what we have just made. Make sure your drawing mode is set to "wireframe." In wireframe
mode, when you select a CP one side will highlight as indicated in Fig. 2. Select the CP I labeled #1, and
press the "," key -- all four CPs will highlight and a bounding box will display around them, this means that
all the CPs are connected to this spline. Next, select the CP I marked as #4 so that the highlight displayes
to the left, like the wireframe example, again press the "," key and now only two CPs highlight, cuz that's all
the CPs there are on this spline! Go back to Fig. 1, and look at example "F." I left tails on each spline so
it would be easy to see the two separate splines. If we delete the tails in "F," we would have the same basic
shape as our current extruded example. Let's turn this into a rectangle, select the entire patch, use any
of the methods we talked about earlier. When all the CPs are highlighted, press the "Peak (P)" Button and
the result will look like the bottom example in Fig. 2. Fun huh? ;-)

Let's make it a 3D box! While it is still highlighted, press the "Extrude (E)" button and then switch views to
left or right, if you want you can reselect the "Snap Manipulator to Grid," and drag the extrusion away from
it's starting location. Select the "Birdseye View" (7 on the keypad) and do a render. You should see a 3D box,
whack the "/" key again and then press "Peak (P)" again, and render again. A now we see a perfect 3D box.

Lastly, for now, if you connect the end CPs of two splines they will join to make a single spline --
that's something to remember, too!

That's all for right now, sometime in the future I will add more, but this should get ya started! Please lemme
know if you found this helpful or condescending... Read the manuals, and other tuts, they should make a little
more sense to you now!

If you learned something from this tutorial, please drop me an E-mail at Jeff Cantin
This is an important step, I track the number of visits to "thank you" notes, I need to know my time and my
web space is well spent.

I have other tutorials linked from my hobby homepage. Give those a try too when you are ready.