To animate the five different balls in 3D we will follow a similar approach to the exercises in 2D. First we need to make a background. This consists of a cube that has been given a sloping top. It is built to the same proportions as the shed in our 2D background (5 units⫻
5 units ⫻4 units). We also need to make a floor for the ball to bounce on. This con- sists of a grid that is the same width as our shed and is long enough to fit all of our ball bounces on (5 units ⫻40 units). This only has to be built once. It can be re-used for each ball we animate.
Then we need to make our balls. These will all be the same size! We want an audience to be able to tell what sort of ball they are from their movement rather than their size. The balls will always be 1/5 the size of the width of the shed.
Each of the balls will have to be constructed with a ‘hierarchy’. A hierarchy is an abstract graphical interpretation of how a model is constructed. It will consist of a ‘parent’ which
could then be linked to any number of ‘children’. Let’s say we have two objects on screen, a big cube and a smaller cube. They will be linked together, in a hier- archy. The large cube is the parent, the smaller cube is the child. When you select the large cube (the parent) and move it, the small cube (the child) will move with it. But when you select
and move the small cube (the child) it will move on its own, leaving the large cube (the parent) behind.
Movement given to the parent will affect all of the children, but movement given to a child will work independently of the parent. The ball hierarchy will consist of three parts, a parent, a child and a child of the child. The parent and the first child will be invisible objects the second child (grandchild?) will be the ball. These invisible objects are devices
that do not render in the final version of your animation. (They are called ‘Point Helpers’ in 3D Studio Max, ‘Locators’ in Maya and ‘Nulls’ in LightWave and Soft|Image XSI.) The first two parts of the hierarchy will have a different ‘movement’ ascribed to them. The parent object will deal with the movement (or translation) of the ball and the first child will deal with the rotation. In order to save confusion it’s a good idea to rename these invisible objects ‘movement’ and ‘rotation’.
First we work out the key positions of the movement (or translation) of the ball and setting keys on the movement part of the hierarchy (this will take the other parts of the hierarchy with it). We do this by following the key positions of our drawn animation. The first key position will be at the top of the shed. This will be on frame 1. So select the movement part of the hierarchy and set key positions on this. The second key position will be just as the ball reaches the end of the shed roof. The frame number of this key position depends on which ball you are animating (with
the bowling ball it’s frame 17). The key position where the ball leaves the roof is on frame 19. The remaining key posi- tions are worked out by measuring the height and the distance travelled by each of the drawn key balls, and then
putting the ball, in the 3D-computer anima- tion program, in the same position and at the same frame number as the drawn key ball. Take all your measurements from the centre of the block for the distance and the height of the ball above the ground. Don’t be afraid to draw on the monitor screen with a ‘chinagraph’ pencil (although I accept no responsibility for
any damage that you may do; don’t draw on a LCD screen). Draw the rough positions onto the screen of where the ball looks like it should go according to your drawn keys and then position the 3D ball underneath.
Once the ‘movement’ key positions are in place the computer will do the in-betweens for us. As we saw in Chapter 1, the in-betweening that the computer does will not be correct. We have to tell it where to put the in-between balls. We do this either by putting in all the in-between balls ourselves or by manipulating the animation curves, as in Chapter 1.
Once the movement is done we can go back over our animation and set keys for rota- tion on the rotation part of the hierarchy. Select the rotation part of the hierarchy and set a key at the very start of the piece of animation. Work out how much the ball will rotate over the length of the scene by measuring the distance travelled in relation to the circum- ference of the ball. Then, go to the very end of the scene, rotate the ball by the correct amount and then adjust the curves to make it look right.
You will find how to animate each of the five sorts of balls in more detail in chapter002 of the CD-ROM in .pdf files that relate to each of the 3D animation programs that are covered in this book. The .pdf files are called 3DS_Max_bouncy_balls.pdf, Maya_bouncy_balls.pdf, LightWave_bouncy_balls.pdf and XSI_bouncy_balls.pdf.