MART Term 3, Lecture 3
Bits & Bobs

The Spreadsheet

Reload the snowing scene, and we'll have a look at yet another useful editor. The spreadsheet only works on the currently selected objects, so go to Edit → Select Hierarchy. Now click on Window → General Editors → Attribute Spread Sheet.

What you'll get is a list of each object in the scene down the left hand side, with different attributes along the top. The names of the various tabs give you an indication of the type of attributes you can expect to find in each tab. The spreadsheet is useful for comparing the attributes of different objects: for example, the intensity of light sources (Shape Keyable tab), the ability of objects to cast shadows (Render tab), and the curve precision (Geometry tab). Notice also that you can change the values in the spreadsheet. If you want to play around with it a bit more, you might want to load a scene with more stuff in it.

Split Your Outliner

[screenshot: MART_T3L03_html_m2cc116f]While we're on the subject of random things that are useful, let's do a couple more. At the bottom of the outliner window there is a "split" that you can drag upwards, and therefore you can be in two different places in it at once.

Virtual Sliders in the Attribute Editor

We know that we can select an attribute in the channel box and use it as a virtual slider with the middle mouse button. This is good. But when we're in the attribute editor it doesn't work. How annoying is that? Very, until you know that in the attribute editor you can ctrl-drag on any of the parameters: dragging with the LMB is normal speed, MMB is fast, RMB is really fast.

IK Splines

IK splines are an easy way to control a long chain of joints using a NURBS curve.

[screenshot: MART_T3L03_html_4ee13612]In an orthographic view, create a long chain of joints (about 10 or so); it doesn't matter how bent or straight it is. Now create a curve (with not too many CVs: about 4 or so) that is roughly the same shape as the chain (only has to be very rough). With nothing selected, go to Skeleton → IK Spline Handle Tool ❐, reset the tool, and turn off Auto Create Curve. Now pick (as it tells you to) the first joint of the chain, the last joint of the chain, and the curve. You'll see the chain jump onto your curve, and you can now control your joint chain using the CVs of your curve. Bear in mind though that your chain has a fixed length but your curve doesn't: thus if your curve gets longer or shorter, the chain either won't reach the end or will stick out over the end.

This is a particularly useful feature for something like a whip: you could have a 50 or 100 bones chain, and control it using 4 or 5 CVs on a curve. IK splines are sometimes used for a character's spine (Tarquin's rig uses one for the small amount of visible spine).

Animation Snapshot

If you remember back to last term, you had a lecture with Adam in which he wrote a script to create a series of dominoes. We're going to do the same thing now, but using a different technique.

[screenshot: MART_T3L03_html_bfbd01f]Get a new scene. First create a plane to put our dominoes on, one domino, and a path that we want them to follow. Select the domino and the path, and go to Animate → Motion Paths → Attach to Motion Path. Now our domino follows the path, but we want it leave a copy of itself as it moves. For this we're going to use the animation snapshot tool.

[screenshot: MART_T3L03_html_349e0dc6]Select the domino and go to Animate → Create Animation Snapshot. In the settings, change the Time Range to Time Slider, and change the Increment to 2. Now press Snapshot: this will take a while, but what you should be left with at the end of it is a beautiful domino rally. Note that this can be carried out on any type of animation, not just motion paths.

Creating a NURBS Shoe

This really nice tutorial for making a high-heeled shoe is in the book Maya 6 Killer Tips1; I thought I'd share it with you. Open this scene:

[screenshot: MART_T3L03_html_3a33fc27]You'll find two curves: a profile curve for the shoe, and a plan of it. We are going to use these curves to create our shoe. I say two curves, there are actually six: four for the side view (it was drawn then chopped up), and two for the plan. Note also that the plan doesn't go all the way round, as we will create half a shoe and duplicate it. We are going to use a birail for this task: the toe and heel curves will be our profile curves, so now all we need are our rails. In order to get them, we will be very cunning.

Select the top and bottom curves and extrude them by 20 units each. Now project the plan curves onto these extrusions (in the top viewport): the inner plan curve onto the top extrusion, and the outer plan curve onto the bottom extrusion.

[screenshot: MART_T3L03_html_2ab9359b]Duplicate these surface curves, and then hide the two surfaces (we could in theory remove them, but that would involve deleting construction history, etc: we shan't bother with that just yet). Also hide all of the original curves except for the toe and the heel curve, and we should be left with a perfect set of birail curves.

[screenshot: MART_T3L03_html_81916a1]Well, not exactly perfect: it seems I wasn't quite precise enough when making the curves, as they don't quite intersect. The only place where they don't is where the toe curve meets the sole of the shoe. Zoom in on this area, select both curves, and press F8 to go into component selection mode. Select the last (actually it's the first, but never mind) point on the side curve, click snap to points on, and drag it to the first point on the toe curve till it snaps.

[screenshot: MART_T3L03_html_40142487]We are now ready to do our birail. Select the two profile curves (toe and heel), then go to Surfaces → Birail → Birail 2 Tool. Follow the instructions in the HelpLine (at the bottom of the screen) until the birail is complete. Then all you have to do is duplicate it (scaling -1 in the x axis) and hide everything else and you're left with the basics of a shoe. Now all it needs is a sole and a heel: you could create these by using various methods, but I made the sole by duplicating an isoparm from the shoe and chopping it up to do a birail for it, and the heel by doing a loft.

Issues with Transparency & Raytracing

While we're on the subject of glass, open this file:

All of these objects have the same texture. Open a render view and see what it looks like. Now check that they do all have the same texture. They do, don't they? So why is the centre of our image grey, when it should be red? The answer is down purely to the renderer.

When a ray of light gets refracted, the renderer has to do twice as many calculations. When it gets refracted again, the renderer does three times as many. This continues for as many refractions as exist. Naturally, the renderer wants to cut down the amount of time it spends rendering each image, so it cuts off the numbers of consecutive refractions that it allows, before giving up (and returning the background colour). Also, particularly with reflections (for which the same thing is true), it is perfectly possible to get into an infinite loop of reflections if the number is not restricted in this way (think of two parallel mirrors with the camera in between).

The number is cut off in two places: in the shader itself (set Raytrace Options / Refraction Limit and Reflection Limit both to 20) and in the options of the renderer (set Raytracing Quality / Reflections and Refractions both to 20), and render again: it should come out looking correct. Note that these settings can dramatically affect render time: only change them if you need to, and when you do, only turn them up as high as you absolutely need.

1HANSON, E., IBRAHIM, K. AND NIJMEH, A., 2004. Maya 6 Killer Tips. United States: New Riders Publishing / Peachpit Press.