Tarquin's Extruder Tutorial Part 3 Turning and tilting the path

By: Tarquin

tarquin@planetunreal.com

Tarquin's UT

Preliminaries
Use the latest build of the extruder (currently 080).
Make sure your red builder brush is reset.
Read parts 1 and 2 of this tutorial!

## Example 3.1

You may have noticed that all the paths we've tried so far have several things in common:

1. The first point has always been zero: the path has remained anchored to the origin.

2. The second point has always been of the form (0,0,a): the path has always started out by going straight up.

3. The y co-ordinate of all path points has always been zero: all paths so far have been restricted to the XZ plane.

We'll start by letting the path bend into the y direction.
These are absolute path points; so make sure the PathSource property is set to Vect_Abs.

`PathPoints[0]=(0,0,0)
PathPoints[1]=(0,0,2)
PathPoints[2]=(2,0,2)
PathPoints[3]=(2,2,2)
`

| The brush with the path points marked out in yellow. The path starts at the origin, then goes up the z axis, then along parallel to the x axis, then turns again to run parallel to the y axis.
| Just the path.
| The brush again, but this time I've deleted edges that are behind to make it look solid. The path points are again picked out in yellow, except the first one at the origin which is hiding from you. Notice how the middle section is mitred in different directions at either end.

## Example 3.2

There's only so many times I'll bake up a tryptich like that in p-shop. The best way to get a feel of these brushes is to build them and do much mouse-waving in the camera view.
Try these points. I've listed them as relative so make sure the PathSource property is set to Vect_Rel. You can press build after entering each point to see how the brush grows section by section.

`PathPoints[0]=(0,0,0)
PathPoints[1]=(0,0,2)
PathPoints[2]=(2,0,2)
PathPoints[3]=(0,0,2)
PathPoints[4]=(0,8,0)
PathPoints[5]=(0,0,-2)
PathPoints[6]=(-2,0,-2)
PathPoints[7]=(0,0,-2)
`

The shape starts on the left of the picture. You can see by looking at the path points that by the time it reaches the end of the path it's been turned through a full 180 degrees.

## Example 3.3

We'll now take a look at a path that doesn't start by going straight up.
For the last example, we used 8 path points, and rather than go through them all typing lots of zeros, we can use the Command Module to reset the path for us: select C_ResetPath from the drop-down list in the _COMMAND property, then press build. All the values in the PathPoints list will be set to zero, and the _COMMAND property will be reset to neutral. Your red builder brush will not change — this command leaves the builder brush alone.

`PathPoints[0]=(0,0,0)
PathPoints[1]=(1,0,2)
`

It doesn't matter what you set PathSource to — a path with only two points has the same vectors in either type (think of pirates!).

The base of the brush tilts over, so the base of the brush is always a true cross-section.
To return to the office building analogy, the floor-plan for the very first storey is always exactly the same as the blue print — it's just that here the architect's dogsbody didn't quite interpret survey data properly and the building is on rather a steep hillside.

## Example 3.4

PathPoints[0]=(0,0,0)
PathPoints[1]=(2,0,2)

The building is now tilting at 45 degrees. Note that you can't get this brush by rotating the previous one: firstly, the distance between the two ends is greater, and secondly the brush from example 3.3 dips at an angle that isn't on UnrealEd's rotation grid.

## Example 3.5

PathPoints[0]=(0,0,0)
PathPoints[1]=(2,0,1)

Tilting even further.

## Example 3.6

PathPoints[0]=(0,0,0)
PathPoints[1]=(2,0,0)

The building is now tilted all the way to horizontal.
Now it gets a little tricky:
Follow the sequence of 4 pictures (making an animated gif of them seemed tacky), looking at the base shape in particular. In the first picture, where it's only tilted a little, the square base is seen from the side.
You can imagine the original shape, the blueprint, lying flat, starting at the origin and extending along the x-axis. It also extends along the y-axis out of the screen, though we have to imagine that.
The x-axis side of the base is gradually tilted, until in the last picture it's pointing downwards, along the negative z-axis. The y-axis side of the base hasn't changed, it still points out of the screen towards us.

It's helpful to imagine the original shape — the blueprint — having its own personal axes, x and y. In this example we've rotated the blueprint to make the base of the brush so its x-axis now points down the world's negative z-axis.
In the next part of the tutorial we'll start building with shapes other than the preset square, and the way in which the blueprint is turned will be important.

Suggestions and comments about this tutorial, and screenshots of things you've extruded for a gallery page are welcome: tarquin@planetunreal.com

© Tarquin 19 April 2001