Visual Basic Games: Week 3

1
Visual Basic Games Week 3

• Global variables, parameters, Select, KeyDown
• Enable, Visible, Focus
• State of Game
• Read chapter 3

2
Global versus Local Variables

• Variables (aka internal variables) hold data
  independent of properties in controls.
• Global variables are defined (persist)
  independently of any particular procedure.
  Declared (using DIM) in the (General) section
  above all the procedures.
• Local variables are defined only persist within
  a procedure.
• Rule local, except when a value must be global.
  
• Rule dont economize on names or length of
  names. Use i, j, n, for simple indexing,
  otherwise use meaningful names.
• Convention use int, sng, bln, etc. as part of
  name.

3
Option Explicit

• Type in as first line in (General) section (this
  is first line in the code window).
• This will force an error if and when you use a
  variable without first declaring it in a DIM
  statement.
• WHY do this? This will warn you of any spelling
  errors.

4
Parameters

• Procedures (such as event procedures or
  procedures you will define yourself in the later
  projects) can have parameters. These are values
  set by VB or by the calling program.
• Sub lblCard_Click(Index as Integer)
• Sub Form_KeyDown(KeyCode as Integer, Shift as
  Integer)
• When you define your own procedures, these two
  facts will be significant (and will be repeated)
• Parameters are call by reference. The called
  procedure can change the value
• The name of the parameter has local scope. The
  name in the calling procedure can be different
  than the name in the called procedure.
• In Cannonball, hittarget is called for two
  different reasons and different names are used.

5
Conditional statements

• IF condition Then
• 1 or more lines of code
• Else
• 1 or more lines of code
• End If
• Select Case expression
• Case 1 or more values OR conditions
• code
• Case 1 or more values or conditions
• code
• Case Else
• code
• End Select

6
Chance game features

• Rules of the game
• Add up values on the dice
• on a first throw, 7 or 11 wins, 2, 3 or 12
  loses. For anything else, the value becomes the
  point
• On follow-up throws, throwing the point again
  means a win. Throwing a 7 means a loss.
• Implications for implementation need to maintain
  information on what the status is. This is called
  the state of the game. The state of the chance
  game is
• Is it a first or a follow-up throw?
• What is the point

7
Chance Design Tasks

• State of the gamedone with global variables
• Get (pseudo-) random valuesuse Randomize and
  Rnd. Also use expression
• Int(Rnd6) 1
• Selectively show images of dicedone with image
  controls, the Visible property, and using an
  extra control in the case of doubles (e.g., two
  2s)
• Display rules command button code MsgBox
• End game use command button code End
• Rules of game done using Select statements
  within Select statement (outer statement
  distinguishes between first throw and follow-up
  throw)

8
Preview Timers

• The timer control has one event timer.
• and two critical properties
• Interval
• Enabled
• The timer event will happen if Enabled is set to
  True and Interval is non-zero. The timer event
  will happen every Interval milliseconds.
• If Interval is set to 500, the timer event will
  happen every ½ second.
• Timer is more like an alarm clock.

9
Top
Left
Top and Left of the bounding rectangle
Top has been increased
10
Moving ball

• Place a timer control on the form (it will not be
  visible). Set interval to 300, enabled to True.
  Place a shape control called shpBall. (make it a
  solid circle).
• Code in timer1.timer
• shpBall.Top shpBall.Top .5shpBall.Height
• Run program. You will need to use the stop
  button to stop it.

11
How to move ball.

• 1000 twips
• up
• left
• right
• How to move ball a different amount?

12
Project control direction of object

• Objective use keys in keypad to set (change)
  direction of moving ball.
• Need
• Way to move (animate) a ball
• Event that signals key down Form_KeyDown
• Key codes associated with the selected keys
• Select statement for specifying action for each
  case
• Way to encode right, left, up, down, and later
  diagonal directions

13
Move a ball

• Do animation using timer control and a start
  button that sets the interval and enables the
  time.
• Code in tmr.Timer (happens every interval)
• shpBall.Top shpBall.Top vspeed
  shpBall.Height
• shpBall.Left shpBall.Left hspeed
  shpBall.Width
• vspeed and hspeed will be changed in the event
  procedure for KeyDown

14
Setting the two speeds

• Sub Form_KeyDown(KeyCode as Integer, Shift as
  Integer)
• Select Case KeyCode
• case leftkey
• hspeed -unit
• vspeed 0
• case upkey
• hspeed 0
• vspeed -unit
• case sekey
• hspeed unit
• vspeed unit
• .

15
Case Else

• Player should be given feedback for a bad
  keystroke
• Case else
• MsgBox Click one of the direction keys
• or (for your own debugging)
• MsgBox You clicked key Str(KeyCode)
• End Select

16
KeyDown

• Need to make sure that the Form_KeyDown event is
  triggered. This requires you do disable (set the
  enabled property to false) other controls on the
  board and also setfocus for the form.
• How do you know to do this I learned from
  experience.

17
cmdStart_Click

• tmrBall.Interval 100
• tmrBall.Enabled True
• cmdStart.Enabled False
• frmControl.SetFocus

18
Form_Load

• unit .3
• upkey 104
• rightkey 102
• downkey 98
• leftkey 100
• nekey 105
• sekey 99
• swkey 97
• nwkey 103

19
How to stop?

• Use a designated key (add to Form_Load)
• stopkey 101
• In the Select Case statement in KeyDown add,
• Case stopkey
• tmrBall.Enabled False
• cmdStart.Enabled True

20
Global variables

• Normally, variables are active / accessible /
  alive just in the local subroutines and functions
• but, you need all these variables to persist
  between events
• vspeed, hspeed are set in KeyDown and used in
  tmrBall.Timer
• leftkey, rightkey, etc. are set in form_Load and
  used in KeyDown
• So, you need to have a DIM statement (called a
  declaration) in the (General) section

21
Review general

• Incremental development
• Important you dont think of things in the
  complete, proper, final order. Divide and
  conquer take the task and divide it into
  subtasks.
• Incremental testing do first with just two
  directions (left and right), then up and down,
  then diagonals, then stop.

22
Review specific

• tmrBall.Timer eventhandler moves the ball using
  the vspeed and hspeed, which were set elsewhere
• form_keydown eventhandler uses cases within a
  select case statement to set vspeed and hspeed
• one of the cases will turn off the timer and
  reset the start button
• cmdStart_Click eventhandler starts off the
  animation by setting tmrBall.Interval and
  tmrBall.Enabled. It also turns itself off (sets
  cmdStart.Enabled to false) and frmControl.Focus
  to True.

23
Assignments

• In lab,
• implement the control exercise or
• work on chance (dice) game
• Work on controlling ball exercise
• Complete chance to show. Work on bouncing ball,
  if you finish chance early.