Const MaxPoints = 20

Global TestMode = 0
Global DB_CurrentPoint = 0

Type TPoint
  Field X#
  Field Y#
End Type

Function TPoint_Create.TPoint( pX#, pY# )
  Local lPoint.TPoint = New TPoint
  lPoint\X = pX
  lPoint\Y = pY
  Return lPoint
End Function

Function TPoint_Destroy( pPoint.TPoint )
  Delete pPoint
End Function



Type TFigure
  Field Constr_.TPoint[ MaxPoints ]
  Field Point_.TPoint[ MaxPoints ]
  Field Acc_.TPoint[ MaxPoints ]
  Field PointCount%
End Type

Function TFigure_Create.TFigure ()
  Local lFigure.TFigure = New TFigure
  lFigure\PointCount = 0
  Return lFigure
End Function



Function TFigure_AddPoint( pFigure.TFigure, pX#, pY# )
  If pFigure\PointCount < MaxPoints Then
    pFigure\PointCount = pFigure\PointCount + 1
    pFigure\Constr_[ pFigure\PointCount - 1 ] = TPoint_Create( pX, pY )
    pFigure\Point_[ pFigure\PointCount - 1 ] = TPoint_Create( pX, pY )
    pFigure\Acc_[ pFigure\PointCount - 1 ] = TPoint_Create( 0, 0 )
    Return True
  Else
    Return False
  EndIf
End Function

Function TFigure_Destroy( pFigure.TFigure )
  For i = 0 To pFigure\PointCount - 1
    TPoint_Destroy( pFigure\Acc_[i] )
    TPoint_Destroy( pFigure\Point_[i] )
    TPoint_Destroy( pFigure\Constr_[i] )
  Next
  Delete pFigure
End Function


Graphics 800, 600, 0, 2
SetBuffer BackBuffer()

Figure.TFigure = TFigure_Create()
TFigure_AddPoint( Figure, 400-100, 300-100 )
TFigure_AddPoint( Figure, 400+100, 300-100 )
TFigure_AddPoint( Figure, 400+100, 300+100 )
TFigure_AddPoint( Figure, 400-100, 300+100 )

While Not KeyDown( 1 )
  Cls
  If KeyHit( 57 ) Then TestMode = 1 - TestMode
  DB_CurrentPoint = (DB_CurrentPoint + MouseZSpeed() + 4 * 4) Mod 4
  Text 1,1,DB_CurrentPoint
  UpdateFigures
  ShowFigures
  Flip
Wend

TFigure_Destroy( Figure )
End




Function UpdateFigures()
  Local lFigure.TFigure
  Local lStress#, lAngle#, lX1#, lY1#, lX2#, lY2#
  For lFigure = Each TFigure
    For i = 0 To lFigure\PointCount - 1
      lFigure\Acc_[i]\Y = lFigure\Acc_[i]\Y + Sgn( 10 - lFigure\Acc_[i]\Y )
      lFigure\Point_[i]\X = lFigure\Point_[i]\X + lFigure\Acc_[i]\X
      lFigure\Point_[i]\Y = lFigure\Point_[i]\Y + lFigure\Acc_[i]\Y
      If lFigure\Point_[i]\X < 0 Then lFigure\Point_[i]\X = 0 lFigure\Acc_[i]\X = -lFigure\Acc_[i]\X * 0.75
      If lFigure\Point_[i]\X > GraphicsWidth() Then lFigure\Point_[i]\X = GraphicsWidth() lFigure\Acc_[i]\X = -lFigure\Acc_[i]\X * 0.75
      If lFigure\Point_[i]\Y < 0 Then lFigure\Point_[i]\Y = 0 lFigure\Acc_[i]\Y = -lFigure\Acc_[i]\Y * 0.75
      If lFigure\Point_[i]\Y > GraphicsHeight() Then lFigure\Point_[i]\Y = GraphicsHeight() lFigure\Acc_[i]\Y = -lFigure\Acc_[i]\Y * 0.75
      If MouseDown( 1 ) Then
        lFigure\Point_[DB_CurrentPoint]\X = MouseX()
        lFigure\Point_[DB_CurrentPoint]\Y = MouseY()
      EndIf
      For j = 0 To lFigure\PointCount - 1
        If i <> j Then
          lX1 = lFigure\Point_[i]\X
          lY1 = lFigure\Point_[i]\Y
          lX2 = lFigure\Point_[j]\X
          lY2 = lFigure\Point_[j]\Y
          lStress = Distance( lX1, lY1, lX2, lY2 ) - Distance( lFigure\Constr_[i]\X, lFigure\Constr_[i]\Y, lFigure\Constr_[j]\X, lFigure\Constr_[j]\Y )
          lAngle = Angle( lX1, lY1, lX2, lY2 )
          lFigure\Point_[i]\X = lFigure\Point_[i]\X + Cos( lAngle ) * lStress / 2
          lFigure\Point_[i]\Y = lFigure\Point_[i]\Y + Sin( lAngle ) * lStress / 2
          lFigure\Point_[j]\X = lFigure\Point_[j]\X - Cos( lAngle ) * lStress / 2
          lFigure\Point_[j]\Y = lFigure\Point_[j]\Y - Sin( lAngle ) * lStress / 2
          If TestMode Then
            lX1 = lFigure\Point_[i]\X
            lY1 = lFigure\Point_[i]\Y
            lX2 = lFigure\Point_[j]\X
            lY2 = lFigure\Point_[j]\Y
            DB_StressCol# = Abs( lStress / 300 )
            Color DB_StressCol * 255, ( 1 - DB_StressCol ) * 255, 20
            Line lX1, lY1, lX1 + Cos( lAngle ) * lStress, lY1 + Sin( lAngle ) * lStress
            Oval lX1 + Cos( lAngle ) * lStress - 3, lY1 + Sin( lAngle ) * lStress - 3, 6, 6, 0
            Color 255, 0, 0
            Oval lX1 + Cos( lAngle ) * lStress / 2 - 3, lY1 + Sin( lAngle ) * lStress / 2 - 3, 6, 6, 0
            Color 225, 125, 0
            Line lX1, lY1, lX1 + Cos( lAngle ) * 25, lY1 + Sin( lAngle ) * 25
            Color 255, 0, 0
            Text lX1 + 3, lY1 + 3, i
            Color 0, 125, 255
            Text lX1 + Cos( lAngle ) * 25, lY1 + Sin( lAngle ) * 25, j
          EndIf
        EndIf
      Next
    Next
  Next
End Function

Function ShowFigures()
  Local lFigure.TFigure
  Color 255, 255, 255
  For lFigure = Each TFigure
    For i = 0 To lFigure\PointCount - 1
      If TestMode Then
        Oval lFigure\Point_[i]\X - 4, lFigure\Point_[i]\Y - 4, 8, 8, 0
      Else
        ;Oval lFigure\Point_[i]\X - 4, lFigure\Point_[i]\Y - 4, 8, 8, 0
        Line lFigure\Point_[i]\X, lFigure\Point_[i]\Y, lFigure\Point_[( i + 1 ) Mod 4]\X, lFigure\Point_[( i + 1 ) Mod 4]\Y
        Text lFigure\Point_[i]\X + 5, lFigure\Point_[i]\Y, i
      EndIf
    Next
  Next
End Function



Function Distance#( pX1#, pY1#, pX2#, pY2# )
  Return Sqr( ( pX2 - pX1 ) ^ 2 + ( pY2 - pY1 ) ^ 2 )
End Function

Function Angle#( pX1#, pY1#, pX2#, pY2# )
  Return ( 450 - ATan2( pX2 - pX1, pY2 - pY1 ) ) Mod 360
End Function