A new feature in AWB 2.2 allows you to produce natural looking interactions of any 3D object with the water surface. This feature is supported by the River object, hence the need for the River.bem plug-in, in order to run it.

This small tutorial contains some tips which are aimed to help you to create a procedurally animated water surface at any level of complexity. The tutorial comes with an AWB project file autumn.awb as well as a small library leaves.odb. Both will allow you to avoid routine work and learn some tricks generating waves quickly and easily. It consists of two parts: (a) River and (b) Animated Leaves.

Note that autumn.awb is a finished project, and you can render any frame, or any sequence of frames to obtain ready-made pictures suitable for movie generation.

The River

In general, all that you have to do is to invoke the so-called "External perturbation" in the river object and "throw" the object to the river. Waves will eminate around the point where the object intersects the river surface. Waves will appear in all subsequent frames after the "moment" of intersection as if the waves were running away gradually decaying with time. These waves behave like real natural waves on the surface of the water: emanating from different sources they interfere with each other. They are swept downstream by the flow of the river and so on.

If you start AWB and open autumn.awb you will see a simple scene with a landscape, sky, river and a number of animated dry leaves.

Look at the river's Properties Page. You will see that a new perturbation called "Circular Waves for Dropped" is attached as a branch to the External Perturbations item. Note that "Allow Perturbations from Scene" button is ON, which means that any scene object (except for the landscape, sky, etc..) will produce waves interacting with the river surface.

Parameters of waves for all scene objects are the same within one and the same perturbation. If you want to exclude some objects from the wave generation procedure, then select them in the standard Exclude Objects dialog.

How to fit various parameters of circular waves to a given scene is a matter of your experience. However, some general tips will be suggested.

It is worth remembering that waves can be clearly seen in a running movie even though it may be difficult to distinguish them from a static picture. Do not set the Amplitude to large numbers.

Usually Wave Spacing must be of the order of 3-5 times greater than the river mesh step, otherwise the river mesh resolution will be insufficient for wave visualization.

Phase Speed must be greater than the river Flow Speed unless the "Ignore Flow" box is checked. This is derived from the physics of waves: if you allow waves to be swept by the flow, they can propagate against the flow only if this condition is valid. Otherwise, running waves degenerate into another kind of perturbation.

If you check Ignore Flow box the waves remain circular as if there is no flow at all.

Every object once immersed in the river will generate trains of waves. Each train is as long as the "Generation" input line reads. This is followed by a still period, lasting in the frames which is determined in the "Relaxation" input line. The wave generation process then repeats again. Set Relaxation to a large number, say, to 1000 to obtain a single wave train.

The Falling Leaves

If you look at leaf 1 - 16 objects you will see that in addition to the usual key-frame animation of their position each one has a Swimming in River modifier, which causes a leaf to swim along the river channel from the initial frame.

The leaf settings are very simple. You have to decide how quickly the leaves will fall down to the river surface and then set two keys into the position track of one leaf. For the movie rate of 15 frames per second, there should be 60 frames between the initial (out of the camera view) and final (at the river surface) leaf position. This seems to be sufficient to create a feeling of leaves falling in the autumn. Next you have to attach the Swimming in River modifier to the leaf and only check Uniform Rotation on the Extra Animation page.

The trick is in the following. Save the leaf to the library. Now you can simply drag and drop as many leaves as you want from the library to the scene. There are two things you have to change in every new leaf you drop to the scene. 1. The horizontal position and the start and finish frames of the key-frame animation. 2. The starting frame for procedural animation in the Swimming in River modifier.

Change the horizontal position of a leaf with the blue Animate button!

The last frame of the key-frame animation must coincide with the starting frame in the Swimming in River modifier.

Perform all manipulations with leaves starting with the initial frame of your animation sequence.

That's all of the tricks in this project. Hope, you find them useful in your future creative work with WorldBuilder.

Michael Skoblin. E-mail: skoblin@digi-element.ru