Microsoft Small Basic

Program Listing: TQL943

List Program

'Lunar Lander
'An example of the power of variabls. The all the code through line 70 sets up varaibles
'that are used to manage the simulation (acccurate to the moon and the apollo landers).
'All user interaction is handle through events - Timer and keyboard
'
'Goal - land on the pad traveling less then 2 meters per second (horizontal and vertical)
'Controls (arrows) up: increases vertical thrust; Left/Right: changes horizontal speed.


GraphicsWindow.BackgroundColor = "black"
displayAreaTop = 70
displayAreaBottom = 425
displayAreaMaxHeight = displayAreaBottom - displayAreaTop
simulatedMaxHeight = 900 'simulated height of displayed screen in meters
displayScale = ((displayAreaMaxHeight * 100) / simulatedMaxHeight) / 100 'Ratio of display height to simulated height as a fraction
GraphicsWindow.PenColor = "white"
GraphicsWindow.Drawline(0,displayAreaTop,GraphicsWindow.Width,displayAreaTop)
GraphicsWindow.Drawline(0,displayAreaTop+displayAreaMaxHeight,GraphicsWindow.Width,displayAreaTop+displayAreaMaxHeight)

hold = GraphicsWindow.FontSize
GraphicsWindow.FontSize = 30
pauseText = Shapes.AddText("-- Paused --")
GraphicsWindow.FontSize = hold
Shapes.HideShape(pauseText)
Shapes.Move(pauseText,320,15)

lander = Shapes.AddEllipse(7,7)
landerHeight = 7
landerWidth = 7

kDnEvent = "False"
kUpEvent = "False"
tTkEvent = "False"

secFrac = 0.10 '1 tenth of a second
intvl = 1000 * secFrac

Timer.Tick = OnTick
Timer.Interval = intvl

GraphicsWindow.KeyDown = OnKeyDown
GraphicsWindow.KeyUp = OnKeyUp

'gravity = 9.81 ' Earth gravity 9.81 m/s^2
gravity = 1.63 'Moon's gravity 1.63 m/s^2
thrustMax = ((0.3924 * 10) * secFrac) '10% of throttle of the real LEM was less then 1/25G. 1/25 of a G = 0.3924; This value times 10 (full thrust), chopped up in to the time slices
thrustIncreaseRate = (thrustMax * secFrac) / 1 'at increase rate it will take three seconds to reach max thrust (max * interval ) = max sliced into 10ths of a second, divided by the number of seconds
thrustCur = 0 'No thrust at start, engine is off
lateralThrustRate = (0.25 * secFrac) 'Lateral thrust is 25% of a G
lateralThrust = 0

safeLandingSpeed = 2 'Landing speed of apollo was 1 m/s

'Lander stats at start of simulation
alt = 750 'meters
hloc = 100 'Horizontal location - arbitrary starting point, with left margin being zero
fuel = 250 'Fuel reserves
vSpd = 0 'Vertical Speed
hspd = 5 'Horizontal speed

padPos = Math.GetRandomNumber(GraphicsWindow.Width-200) + 100 'Location of landing pad (closest waypoint)
GraphicsWindow.DrawRectangle(padPos-5,displayAreaBottom,10,5)

textColor = "white"

GraphicsWindow.BrushColor = textColor
GraphicsWindow.DrawText(0,0, "V-Speed:")
GraphicsWindow.DrawText(0,20, "Thrust:")
GraphicsWindow.DrawText(0,40, "H-Speed:")
GraphicsWindow.DrawText(125,0, "Altitude:")
GraphicsWindow.DrawText(125,20,"Distance:")
GraphicsWindow.DrawText(125,40,"Fuel:")

displayStats()

'--- Events and Subroutines to follow ---------------------------------------------------------------

'Events -----------------------------------
Sub OnTick 'Timer event - Update simulation once ever time slice
If kUpEvent = "False" And kDnEvent = "False" And tTkEvent = "False" Then
tTkEvent = "True"
updateStats()
displayStats()
landingCheck()
updateSimulation()
tTkEvent = "False"
EndIf
EndSub

Sub OnKeyDown 'Keydown Event - Process controls
If kUpEvent = "False" And kDnEvent = "False" And tTkEvent = "False" Then
kDnEvent = "True"
If GraphicsWindow.LastKey = "Up" Then
thrustKeyPressed = "True"
ElseIf GraphicsWindow.LastKey = "Left" then
lateralThrust = lateralThrustRate * -1
elseif GraphicsWindow.LastKey = "Right" then
lateralThrust = lateralThrustRate
elseif GraphicsWindow.LastKey = "I" then
zoomIn()
elseif GraphicsWindow.LastKey = "O" then
zoomOut()
ElseIf GraphicsWindow.LastKey = "P" then
If Timer.Interval <> intvl then
Shapes.HideShape(pauseText)
Timer.Interval = intvl
Else
Shapes.ShowShape(pauseText)
Timer.Interval = 100000000 ''if game paused, shut down the event
EndIf
EndIf
kDnEvent = "False"
EndIf
EndSub

Sub OnKeyUp 'Shut down any key generated actions
If kUpEvent = "False" And kDnEvent = "False" And tTkEvent = "False" Then
kUpEvent = "True"
If GraphicsWindow.LastKey = "Up" Then
thrustKeyPressed = "False"
ElseIf GraphicsWindow.LastKey = "Left" Then
lateralThrust = 0
ElseIf GraphicsWindow.LastKey = "Right" then
lateralThrust = 0
EndIf
kUpEvent = "False"
EndIf
EndSub

'Subroutines ------------------------------
Sub updateStats 'Update values controling the simulation (thrust, speed, altitude, etc)
If thrustKeyPressed Then
If fuel >= 0 Then
thrustCur = thrustCur + thrustIncreaseRate
If thrustCur > thrustMax Then
thrustCur = thrustMax
EndIf
fuel = fuel - thrustCur
vSpd = vSpd - thrustCur
Else
thrustCur = 0
fuel = 0
EndIf
Else
thrustCur = thrustCur / 2
If thrustCur < thrustIncreaseRate Then
thrustCur = 0
EndIf
EndIf
hspd = hspd + lateralThrust

hloc = hloc + (hspd * secFrac) ' Horizontal location

padDist = Math.Abs(padPos - hloc)
vSpd = vSpd + (gravity * secFrac)
alt = alt - (vSpd * secFrac)
If alt < 0 Then
alt = 0
EndIf

EndSub

Sub zoomIn
tTkEvent = "True" 'Suspend events
kUpEvent = "True"
kDnEvent = "True"
zoomFrames = 15
zh = 30
zw = 100
zHmax = displayAreaMaxHeight
zWmax = GraphicsWindow.Width
zHmid = displayAreaTop + (zHmax / 2)
zWmid = zWmax / 2

penWhold = GraphicsWindow.PenWidth
penChold = GraphicsWindow.PenColor
penBhold = GraphicsWindow.BrushColor
GraphicsWindow.BrushColor = "Black"
For zi = 1 To zoomFrames
GraphicsWindow.PenWidth = 2
GraphicsWindow.PenColor = "white"
GraphicsWindow.DrawRectangle(zWmid - zw / 2, zHmid - zh / 2, zw, zh)
pmPause = 100
pauseMe()
GraphicsWindow.PenWidth = 4
GraphicsWindow.PenColor = "black"
GraphicsWindow.FillRectangle(zWmid - zw / 2, zHmid - zh / 2, zw, zh)

zh = zh + ((zHmax-30) / zoomFrames)
zw = zw + ((zWmax-100) / zoomFrames)
EndFor
GraphicsWindow.BrushColor = penBhold
GraphicsWindow.PenColor = penWhold
GraphicsWindow.PenWidth = penChold
tTkEvent = "False" 'Resume events
kUpEvent = "False"
kDnEvent = "False"
EndSub

Sub pauseMe
pmstart = Clock.ElapsedMilliseconds
While Clock.ElapsedMilliseconds - pmstart < pmPause
EndWhile
EndSub

Sub zoomOut
holdtm = Timer.Interval
Timer.Interval = 100000000
hold = GraphicsWindow.PenColor
GraphicsWindow.PenColor = "white"
holdbrush = GraphicsWindow.BrushColor
GraphicsWindow.BrushColor = "black"
displayAreaMiddle = (displayAreaTop + (displayAreaMaxHeight / 2))
fstWidth = 50
zoomHeight = displayAreaMaxHeight
stps = 10
For zi = GraphicsWindow.Width To fstWidth Step -((GraphicsWindow.Width - fstWidth) / stps)
GraphicsWindow.FillRectangle(0,displayAreaTop,GraphicsWindow.Width,displayAreaMaxHeight)
zoomHeight = zoomHeight - (displayAreaMaxHeight-50) / stps
GraphicsWindow.DrawRectangle((GraphicsWindow.Width / 2) - (zi/2), displayAreaMiddle - (zoomHeight / 2) ,zi,zoomHeight)
Program.Delay(50)

EndFor
GraphicsWindow.PenColor = hold
GraphicsWindow.BrushColor = holdbrush
Timer.Interval = holdtm
EndSub


Sub landingCheck 'Check if ship has reached the ground
If alt < 1 Then
Timer.Interval = 100000000 'If the ship has landed, shut down the event
displayFinish()

alt = 0
thrustCur = 0
displayStats()
EndIf
EndSub

Sub displayFinish
hold = GraphicsWindow.FontSize
GraphicsWindow.FontSize = 50
If vSpd < safeLandingSpeed and Math.Abs(hspd) < 2 And Math.Abs(padDist) < 5 then
GraphicsWindow.DrawText(0,150, "Touch Down")
Else
GraphicsWindow.DrawText(0,150, "Boom")
EndIf
GraphicsWindow.FontSize = hold
EndSub

Sub updateSimulation 'Change the ship display based on the status of the simulation
landX = hloc
landX = landX - (landerWidth / 2) 'Center the lander over its horizontal location
landY = (displayAreaBottom - (alt * displayScale))
landY = landY - landerHeight 'Place the lander above its vertical location
Shapes.Move(lander,landX,landY)
EndSub

Sub displayStats 'Display the current values of simulation values
GraphicsWindow.BrushColor = "black"
GraphicsWindow.FillRectangle(60,0,60,60)
GraphicsWindow.FillRectangle(185,0,60,60)
GraphicsWindow.BrushColor = textColor

displayNumber = vSpd
convertNumberForDisplay()
GraphicsWindow.DrawText(60,0,Text.GetSubTextToEnd(displayNumberText,2))

displayThrustMeter()
displayNumber = thrustPercent 'calcuated during the meter display
convertNumberForDisplay()
displayNumberText = displayNumberText + "%"
GraphicsWindow.DrawText(60,20,Text.GetSubTextToEnd(displayNumberText,2))

displayNumber = hspd
convertNumberForDisplay()
GraphicsWindow.DrawText(60,40,Text.GetSubTextToEnd(displayNumberText,2))

displayNumber = alt
convertNumberForDisplay()
GraphicsWindow.DrawText(185,0,Text.GetSubTextToEnd(displayNumberText,2))

displayNumber = padDist
convertNumberForDisplay()
GraphicsWindow.DrawText(185,20,Text.GetSubTextToEnd(displayNumberText,2))

displayNumber = fuel
convertNumberForDisplay()
GraphicsWindow.DrawText(185,40,Text.GetSubTextToEnd(displayNumberText,2))
EndSub

Sub displayThrustMeter 'Display a graphic interpretation of the current thrust level
meterWidthMax = 60
thrustPercent = (thrustCur * 100) / thrustMax 'Percentage that current thrust is of max thrust
meterWidth = (meterWidthMax * thrustPercent) / 100 'with of the meter matching percentage of current thrust
GraphicsWindow.BrushColor = "red"
GraphicsWindow.FillRectangle(60,20,meterWidth,16)
GraphicsWindow.BrushColor = textColor
EndSub

Sub convertNumberForDisplay 'Convert a number for display, always with two decimal places
displayNumber = displayNumber * 100
displayNumber = Math.Round(displayNumber)
displayNumber = displayNumber / 100

displayNumberText = "A" + displayNumber 'Added to force small basic to interpret as text and prevent the trailing zeros from being removed
dotLoc = text.GetIndexOf(displayNumberText,".")
If dotLoc = 0 Then
displayNumberText = displayNumberText + ".00"
ElseIf dotLoc = Text.GetLength(displayNumberText) - 1 then
displayNumberText = displayNumberText + "0"
EndIf
EndSub