Putting Objects in
Motion
Using Method Calls
Copyright © 2005-2011 Curt Hill
Overview
• Each object is prepared to do
certain things
• A method call uses one of these
behaviors
• Since Alice is mostly about 3D
animations these are mostly about
moving in some way
• This presentation uses existing
methods
– We later see creating our own
Copyright © 2005-2011 Curt Hill
Objects Again
• Each actor, such as a fish, is an
object
• Any object may have methods that
cause it to do something useful,
such as move in some direction
• An object may actually be composed
of objects
– A hand has actions different than the
whole body
– Yet moving the whole body must also
move the hand
Copyright © 2005-2011 Curt Hill
Screen Shot
• The next two screens show a
program in the process of creation
• The objects to be manipulated are
listed
• The first shows the fish as selected
– It is surrounded by its bounding box
• Bottom left shows the methods that
can be used
• After that the sub-object of the fish
are shown Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Programming
• The programming of this system is
causing the actors to move properly
• Errors are called bugs
• A bug in Alice results in a scene that
does not unfold as intended
• Causing an object to move is to
execute the move method
• This is done using drag and drop
Copyright © 2005-2011 Curt Hill
Getting things to move
• Click on the object to select it
• Drag the action from the details
pane to the method pane
• Fill in the needed parameters if there
are any
• Test it by hitting the play button
• The order of the actions in the
method pane determine how they
are executed
Copyright © 2005-2011 Curt Hill
Adding an Action
• What follows are four screens that
show how to add action to a scene
• Select the object to be acted on
• Drag the move method to the
Method Pane
• Choose Forward and the distance
• Finally what the program looks like
when this instruction has been
added
Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Copyright © 2005-2011 Curt Hill
Concurrency
• Concurrency is two or more things
happening at the same time
• It is a fancy Computer Science term
that we usually do not teach until
students are quite experienced
• Except in Alice!
• Here we have a Do Together that
does concurrency
– Makes it look easy
Copyright © 2005-2011 Curt Hill
Do Together
• The Do Together tab is at the bottom
of the Method pane along with:
–
–
–
–
–
Do In Order
If Else
Loop
While
etc
• All of these are containers for other
statements
Copyright © 2005-2011 Curt Hill
Containers
• A container is a statement that
contains other statements
• When it is drug onto the pane it
contains nothing
• You then drag statements into it
– These can be existing statements or
new ones
Copyright © 2005-2011 Curt Hill
Do in Order
• Another container
• This forces actions to be performed
in order
• Use Do Together to do things
simultaneously and Do in Order to
do things sequentially
• Any of the containers may be in
another
– A Do in Order could be inside a Do
Together
Copyright © 2005-2011 Curt Hill
Demo
• Now lets get things moving
• Instead of a 3D post card we get a
3D animation
• Use methods of move, roll, turn
• Use Do Together and Do In Order
Copyright © 2005-2011 Curt Hill