Transcript Lecture notes (5-1)

CS320n –Visual Programming
Interactive Programs
Mike Scott
(Slides 5-1)
What We Will Do Today
• Learn about interactive programs
• Learn how to add events to Alice programs
to make them interactive
Visual Programming
Interactive Programs
2
Control of flow
• Control of flow – how the sequence of
actions in a program is controlled
– what actions happen first, second, third
• In movie style programs as shown in
chapters 1-4 the sequence of actions is
determined by the programmer
– create a story board design
– implement the program methods to carry out
the designed sequence
– completely predictable
Visual Programming
Interactive Programs
3
Interactive Animations
• In interactive programs, the sequence of
actions is determined at runtime when
the user provides input
– clicks the mouse
– presses a key on the keyboard
• Other sources of input are possible
– depending on your computer system
Visual Programming
Interactive Programs
4
Interactive games
• In a video game where the user is guiding a
spaceship, the sequence of actions…
– depends on what direction the user guides the ship
– how fast the user presses the controls.
• Each time the program runs, user input may
cause a different sequence of actions from
previous executions of the program.
• In essence, control of flow is now “in the
hands of the user.”
Visual Programming
Interactive Programs
5
Events
• Each time the user provides some sort of
input, we say an event is generated.
– An event is “something that happens”
– Magically the operating system passes
information about the event to our program
Interactive Program from appendix
What happens when space pressed and
method is not done?
Visual Programming
Interactive Programs
6
event handlers
• An event may
– Trigger a response, or
– Move objects into positions that create
some condition (e.g., a collision) that
triggers a response.
• A method is called to carry out the
response. We call this kind of method
an event handler.
• When an event is linked to an event
handler, a behavior is created.
Visual Programming
Interactive Programs
7
How does this affect your program?
• We want to be able to write interactive
programs
– they can be more interesting than animations
• The approach will be the same as before,
but the difference is that we must now be
concerned with behaviors
– input from the user -> (events)
– how objects respond to an event
-> (event handler methods)
Visual Programming
Interactive Programs
8
Example
• Build an air show flight simulator. In an air
show, the pilot uses biplane controls to perform
acrobatic stunts.
Visual Programming
Interactive Programs
9
Problem
• The whole idea in a flight simulator is to
allow the user to control the flight path.
• The problem is: how do we write our
program code to provide a guidance
system that allows the user to be the pilot?
Visual Programming
Interactive Programs
10
Solution
• Use keyboard input
– Up-arrow key to move the biplane forward
– Spacebar to make the biplane do a barrel
turn
(Note: other sets of keys could be used, we just
arbitrarily picked a couple of keys on the keyboard.)
• Write event handler methods that respond to
each key press
Visual Programming
Interactive Programs
11
Storyboards
• Since two keys are used, two events are
possible – so two storyboards are needed:
Event: Spacebar press
Event:: Up Arrow key press
Response:
Do together
roll biplane a full revolution
play biplane engine sound
Response:
Do together
move biplane forward
play biplane engine sound
Each storyboard outlines an event handler
that responds to a particular event.
Visual Programming
Interactive Programs
12
Demo
• A demonstration of building the biplane
acrobatic simulation
– flyForward
– barrel
Visual Programming
Interactive Programs
13
biplane.flyForward
• Coordinate duration of move and play sound
instructions by matching the duration of the
move to the duration of the sound
Visual Programming
Interactive Programs
14
Events Editor - Linking
• Each event handler
method must be
linked to an event
• click “create new
event” button in
event window
• a template is created
Visual Programming
Interactive Programs
15
Events Editor - Linking
• Select which key
triggers the event
• Select which method
in the program should
be called when the
event occurs
Visual Programming
Interactive Programs
16
Testing
• Test event handler methods as they are
developed.
• Write a method and test it, write a method
and test it, and so on… (this is a technique
called incremental development).
Visual Programming
Interactive Programs
17
Adding More to Flight Simulator
•
•
•
•
flyRight
flyLeft
loop
alternate means of control
Visual Programming
Interactive Programs
18