Option_Explicit



Screen _NewImage(800, 600, 32)



Type Circle

    x As Single

    y As Single

    dx As Single

    dy As Single

    radius As Integer

    color As _Unsigned Long

    lastBumpedAgainstEdges As Single

End Type



' $Dynamic

Dim Shared circles(0) As Circle, quit As _Byte



' Initialize with 5 circles

Randomize Timer

InitializeCircles (5)



Do

    Cls

    UpdateCircles

    DrawCircles

    HandleInput



    _Display

    _Limit 60

Loop Until quit ' ESC key to exit



System



Sub InitializeCircles (numCircles As Integer)

    Dim i As Integer

    For i = 1 To numCircles

        AddCircle

    Next i

End Sub



Sub InitializeCircle (c As Circle)

    Dim j As Integer, i As Integer

    Dim oops As _Byte



    Do

        'loop until we create a circle that doesn't spawn in a collision

        c.x = Rnd * _Width

        c.y = Rnd * _Height

        c.dx = (Rnd - 0.5) * 10

        c.dy = (Rnd - 0.5) * 10

        c.radius = 10 + Rnd * 20

        c.color = _RGB32(Rnd * 255, Rnd * 255, Rnd * 255)



        ' Check collision with other circles

        oops = 0

        For j = 1 To UBound(circles) - 1

            oops = CheckCollision(c, circles(j))

            If oops Then Exit For

        Next j

    Loop While oops



    ' Bounce off edges - prevents newborn circles from getting stuck to the edges

    i = UBound(circles)

    If circles(i).x - circles(i).radius <= 5 Or circles(i).x + circles(i).radius >= _Width - 5 Then

        circles(i).dx = -circles(i).dx

        circles(i).lastBumpedAgainstEdges = Timer

    End If



    If circles(i).y - circles(i).radius <= 5 Or circles(i).y + circles(i).radius >= _Height - 5 Then

        circles(i).dy = -circles(i).dy

        circles(i).lastBumpedAgainstEdges = Timer

    End If

End Sub



Function timeElapsedSince! (startTime!)

    If startTime! > Timer Then startTime! = startTime! - 86400

    timeElapsedSince! = Timer - startTime!

End Function



Sub UpdateCircles

    Dim i As Integer, j As Integer, oops As _Byte



    For i = 1 To UBound(circles)

        circles(i).x = circles(i).x + circles(i).dx

        circles(i).y = circles(i).y + circles(i).dy



        ' Bounce off edges

        If timeElapsedSince(circles(i).lastBumpedAgainstEdges) > 1 Then

            If circles(i).x - circles(i).radius <= 5 Or circles(i).x + circles(i).radius >= _Width - 5 Then circles(i).dx = -circles(i).dx

            If circles(i).y - circles(i).radius <= 5 Or circles(i).y + circles(i).radius >= _Height - 5 Then circles(i).dy = -circles(i).dy

        End If



        If circles(i).x - circles(i).radius <= 0 Or circles(i).x + circles(i).radius >= _Width Or circles(i).y - circles(i).radius <= 0 Or circles(i).y + circles(i).radius >= _Height Then

            'brother's lost

            Dim c As Circle

            c.x = Rnd * _Width

            c.y = Rnd * _Height

            c.dx = (Rnd - 0.5) * 10

            c.dy = (Rnd - 0.5) * 10

            c.radius = 10 + Rnd * 20

            c.color = _RGB32(Rnd * 255, Rnd * 255, Rnd * 255)

            circles(i) = c

        End If





        ' Check collision with other circles

        For j = 1 To UBound(circles)

            If j = i Then _Continue

            oops = CheckCollision(circles(i), circles(j))

            If oops Then

                ' Collision detected, swap velocities

                Swap circles(i).dx, circles(j).dx

                Swap circles(i).dy, circles(j).dy

            End If

        Next j

    Next i

End Sub



Function CheckCollision%% (c1 As Circle, c2 As Circle)

    Dim dx As Single, dy As Single, distance As Single

    dx = c1.x - c2.x

    dy = c1.y - c2.y

    distance = Sqr(dx * dx + dy * dy)



    CheckCollision%% = (distance <= c1.radius + c2.radius)

End Function



Sub DrawCircles

    Dim i As Integer



    For i = 1 To UBound(circles)

        Circle (circles(i).x, circles(i).y), circles(i).radius, circles(i).color

        Paint (circles(i).x, circles(i).y), circles(i).color, circles(i).color

    Next i

End Sub



Sub HandleInput

    Dim k As Long

    k = _KeyHit



    Select Case k

        Case 27

            quit = -1

        Case 32 ' Spacebar adds a circle.

            AddCircle

        Case 82, 114 ' 'R' or 'r' removes a circle.

            RemoveCircle

    End Select

End Sub



Sub AddCircle

    Dim n As Integer



    n = UBound(circles) + 1

    ReDim _Preserve circles(1 To n) As Circle

    InitializeCircle circles(n)

End Sub



Sub RemoveCircle

    Dim n As Integer



    n = UBound(circles)

    If n > 1 Then ReDim _Preserve circles(1 To n - 1) As Circle

End Sub

Quote:0-10 $Debug by menu or typed as first line of code
activating Debug  with F4 key (list of Watch) with F7 and with F8
Executing program line by line using F7 key
observe index of line in execution (triangle and highlighted line of code)
F8 step over for running one loop step (running once all the instructions in a loop)
F6 step out (sub/Function) for running until flow runs out of sub/function
F5 flow the code to debug loops and I/O with user

14.40 breakpoints to stop flow of code and observe status of application (output and variables)

23.30 use debug to find bottlenecks in the code

26.40 Adding watches for inspecting variables
      watching UDT made by TYPE...END TYPE, chosing elements to be observed
      whatching Arrays, chose elements of array to be observed

41.03 changing value of variables to test specific conditions

43.40 set next line to be executed

45.15 see the variables of a specific subprocedure

49.10 F7 runs a Whole line of code also if it has many commands separated by colon

49.30 Observe a variable setting a condition of its value or range of value

58.50 remove a condition of watching about a variable