CRE Programming Club Class 7
Robert Eckstein and Robert Heard
Understanding Events
Certain objects in Small Basic have events
that you can “subscribe” to.
In order to subscribe to an event, create a
subroutine, then assign the name of the
subroutine to the event in the object.
Whenever the event happens, the subroutine
is called to “handle” the event. This can be
almost never, or several times a second.
Events
Events are something in computers that we
call interrupts.
With an interrupt, everything is going smoothly
in the main program, until something outside
the program needs to get the program’s
attention.
At that point, execution in the main program is
brought to a halt, and the subroutine that
handles the interrupt is run.
Import VSX414
GraphicsWindow.KeyDown = handleKeyPress
GraphicsWindow.Show()
looping = "True"
While (looping)
TextWindow.WriteLine("Happily looping...")
Program.Delay(500)
EndWhile
Sub handleKeyPress
TextWindow.WriteLine("Key Down is " + GraphicsWindow.LastKey)
EndSub
Adding... Import PDG320
GraphicsWindow.KeyDown = handleKeyPress
GraphicsWindow.KeyUp = handleKeyUp
GraphicsWindow.MouseMove = handleMouseMove
GraphicsWindow.MouseDown = handleMouseClick
GraphicsWindow.Show()
looping = "True"
While (looping)
TextWindow.WriteLine("Happily looping...")
Program.Delay(1000)
EndWhile
Import PDG320
Sub handleKeyPress
TextWindow.WriteLine("Key Down is " + GraphicsWindow.LastKey)
EndSub
Sub handleKeyUp
TextWindow.WriteLine("Key Up is " + GraphicsWindow.LastKey)
EndSub
Sub handleMouseMove
TextWindow.WriteLine("Mouse is at " + GraphicsWindow.MouseX + "," +
GraphicsWindow.MouseY)
EndSub
Sub handleMouseClick
TextWindow.WriteLine("Mouse is clicked")
EndSub
These Are the Key
Lines...
GraphicsWindow.KeyDown = handleKeyPress
GraphicsWindow.KeyUp = handleKeyUp
GraphicsWindow.MouseMove = handleMouseMove
GraphicsWindow.MouseDown = handleMouseClick
They assign subroutines to these events....
The Program Object
Program.Delay(time) - This will cause the
program to wait for a certain amount of time,
specified as a number in milliseconds.
Program.End() - This will cause the program to
immediately terminate.
Timer
There is also a Timer object if you want Small Basic to let you
know when a certain amount of time has passed. You tell the
object how often the time interval is, and give it the name of a
subroutine.
Timer.Interval = 1000
Timer.Tick = OnTimerTick
Sub OnTimerTick
TextWindow.WriteLine(“Timer has ticked”)
EndSub
The Timer Object
Why Would You Use This?
Perhaps you have a clock in your program
that needs to count down or up every
second...
You can also use it to help show an obstacle
or enemy in your game. (A new one comes
on screen every 3 seconds.)
The Sound Object
Look at the reference documentation for the
Sound Object
Small Basic gives you the ability to play some
elementary or complex sounds.
A bell ringing, a chime, and a click are three of
the sounds that you get for “free” with Small
Basic.
Import QRL274
looping = "True"
While (looping)
Program.Delay(3000)
Sound.PlayBellRing()
TextWindow.WriteLine("Playing bell ring")
Program.Delay(3000)
Sound.PlayChime()
TextWindow.WriteLine("Playing chime")
Program.Delay(3000)
Sound.PlayBellRingAndWait()
TextWindow.WriteLine("Played bell ring")
EndWhile
What’s the Difference
Between Play and
PlayAndWait?
The Play() operations will play the sound and
immediately continue running the program
(even if the sound hasn’t finished yet).
The PlayAndWait() operations will play the
sound and stop the program until the sound
has completed playing.
Why would you want to use either one?
Import XMV444
filepath = "http://creprogramming.com/sounds/a.wav"
Sound.PlayAndWait(filepath)
Sound.Play(filepath)
Program.Delay(1000)
Sound.Pause(filepath)
Program.Delay(1000)
Sound.Play(filepath)
Program.Delay(500)
Sound.Pause(filepath)
Program.Delay(500)
Sound.Play(filepath)
Program.Delay(500)
Sound.Stop(filepath)
We Can Play a Sound,
Pause It, Continue
Playing It, and Stop It
The Sound.Play() operation will start to play
the sound, and immediately continues
running the program.
The Sound.Pause() operation pauses the
sound.
The Sound.Stop() operation stops and resets.
The Text Object
Look at the reference documentation for the
Text object
The Text object allows you to manipulate
Strings.
We can get the length of a string, append to it,
check for text inside of it, etc.
Text - Import LKW972
TextWindow.Write("Enter a valid e-mail address: ")
EmailID = TextWindow.Read()
m = Text.IsSubText(EmailID, ".")
n = Text.IsSubText(EmailID, "@")
If (m = "True") And (n = "True") Then
TextWindow.WriteLine("Valid e-mail address.")
Else
TextWindow.WriteLine("Invalid e-mail address.")
EndIf
What is SubText?
Text.isSubText(text, subText) - Gets whether
or not a given subText is a subset of the larger
text.
Text.GetSubText(text, start, length) - Gets a
sub-text from the given text.
Text.GetSubTextToEnd(text, start) - Gets a
sub-text from the given text from a specified
position to the end.
More Text Operations
Text.GetIndexOf(text, subText) - Finds the
position where a sub-text appears in the
specified text.
Text.ConvertToLowerCase(text) - Converts
the given text to lower case.
Text.ConvertToUpperCase(text) - Converts
the given text to upper case.
Names - Import JFG395
TextWindow.Write("Enter your full name: ")
Name = TextWindow.Read()
c = Text.GetIndexOf(Name, " ")
firstName = Text.GetSubText(Name, 1, c-1)
lastName = Text.GetSubTextToEnd(Name, c+1)
TextWindow.WriteLine("First name: " + firstName)
TextWindow.WriteLine("Last name: " + lastName)
How Did We Separate
The Names?
We asked the Text object to locate the first
instance of a “space” in the string.
We then took the substring from position 1 up
to the position before the space (c-1) and
made that the first name.
We took the substring from position c+1 to the
end and made that the last name.
Assignment
Create a Timer that calls a subroutine every 5
seconds. In that subroutine, play the bells
sound...unless it’s been 30 seconds, at which
point, you should play the chimes instead.
Or… create a shape on top of a graphics
window that will move up, down, left, and right
if you press the arrow keys. Create a “wrap
around” if the shape goes off the edge of the
screen.
Next Time...
We’re going to learn about stacks and the
main game loop.