MCS-170 The Nature of Computer Science

Alice Lecture 5

Object Creation: So far, we have used the Classes of Objects that we find in the Local Gallery. There is an extensive collection of Classes available online. These can be accessed from within the Gallery directory. Within the Alice program, click on Home when adding an Object. There will be two (or more) directory icons - one of these is the Local Gallery, which resides on the computer on which Alice is running. Another will be called Web Gallery. This directory contains Classes that you can access at the central Alice website.

Example: Use the Web Gallery to create a water world with a shark, manta ray, coral, and fish, along with an ocean floor object.

Object and Scene Manipulation: Often, it is hard to see how to position objects in our scene. We can create multiple "views" of the scene by using the Quad View feature of Alice. In the upper right corner of the Alice window we select "quad view" to change the viewing window into a four-pane viewing window. The viewpoints show the scene from (in counter-clockwise order from the upper-left window) The Camera's view, The Top of the scene, The Front of the scene, and The Right of the scene.

Note that the toolbox of mouse controls now has a second row with two new buttons -- a scroll button and a zoom button. These two buttons can be used to adjust the three non-camera viewpoints.
Example: In our fishy example, go to Quad view and use the controls to position the shark above the coral and then position the manta ray and fish to the right of the shark, about five meters away. Have the shark face in the direction of the other creatures.

Object Posing -- It is often tedious to use move, turn, roll commands to make an object transform in some way, for example to have a person raise their arm. For this reason, Alice allows one to pose objects and then recall the poses at later points in the animation. To pose an object, we click on the capture pose button in the Details panel of the object. Then, we can drag the new pose tile that gets created into an animation.

Example: In our fishy example, suppose we want the shark to swim toward the fish, open its mouth and the fish to raise its flippers in alarm. Here (sharkPose.a2w) is a world where we create two poses for this behavior.
Note: It is often difficult to click precisely on an object to pose its parts. There is another way to manipulate an object -- using popup menus.

Example: Suppose we want to make the dorsal fin of our fish twice as big. It is difficult to get the mouse to click on the dorsal (as it is tiny) to select it. Another way to select it is to select it from the Class tree list in the upper left corner of the Alice window. Then, if we right-click on the dorsal fin tab, a menu will popup, allowing us to do a wide variety of actions on the dorsal fin.

Controlling the camera can be one of the more difficult parts of using Alice. Here are a few pointers:
Setting the point of view: Every good director knows that a dynamic film needs to have the camera move within the scene, from one point of view to another. This can be accomplished by dropping dummy objects at positions where you want the camera.

Example: A scene with a three bunnies, where we want to move the point of view from one to another. Drop 4 dummy objects for camera - 1 at initial position, and three at each bunny. (Demonstrate) Here is an example world (bunnyCamera.a2w)

Tracking an object: We can have the camera track an object in the scence by telling the camera to constrain to point at the object.

Example: In our biplane example (biplane.a2w)from the Event Handling lecture, we use this camera method to have the camera track the plane, making sure the duration of the method is long enough to last out the scene.