help moving a sprite in a ellipse

[bplus]

Here is one sprite in constant ellipse Y- and b+ constantly tilting ellipse by a degree after every orbit:

Code: (Select All)

_Title "Experiment with Ellipse draw sprite" 'b+ 2023-07-05

Type xy

    As Single x, y

End Type



Screen _NewImage(800, 600, 32)

_ScreenMove 250, 60

ReDim ell(0) As xy, ell2(0) As xy

MapEllipse 400, 300, 250, 100, ell() '  x,y track for b+

MapEllipse 400, 300, 100, 250, ell2() ' x,y track for Y-

Sprite = _NewImage(40, 40, 32)

_Dest Sprite

Line (0, 0)-(39, 39), &HFF0000FF, BF

_PrintMode _KeepBackground , Sprite

_PrintString (12, 12), "b+"

Sprite2 = _NewImage(40, 40, 32)

_Dest Sprite2

Line (0, 0)-(39, 39), &HFFFFFF00, BF

_PrintMode _KeepBackground , Sprite2

Color &HFF000000

_PrintString (12, 12), "Y-"



_Dest 0

Dim temp As xy

While _KeyDown(27) = 0

    Line (0, 0)-(_Width, _Height), &H05000000, BF

    frame = frame + 1

    If frame = 360 Then frame = 0: tilt = tilt + 1

    Rotate 400, 300, ell(frame).x, ell(frame).y, tilt, temp

    _PutImage (temp.x, temp.y)-Step(_Width(Sprite), _Height(Sprite)), Sprite, 0

    _PutImage (ell2(frame).x, ell2(frame).y)-Step(_Width(Sprite), _Height(Sprite)), Sprite2, 0

    _Display

    _Limit 120

Wend



Sub MapEllipse (xc, yc, xRadius, yRadius, a() As xy)

    ReDim a(360) As xy

    For a = 0 To _Pi(2) Step _Pi(2 / 360)

        a(i).x = xc + xRadius * Cos(a)

        a(i).y = yc + yRadius * Sin(a)

        i = i + 1

    Next

End Sub



Sub Rotate (cx, cy, x, y, degAng, a As xy)

    'cx, cy is center of rotation

    'x, y the point to rotate

    'degAng the angle in degrees to rotate

    ' output a.X, a.Y ' our point of rotation

    d = _Hypot(cx - x, cy - y) ' distance between xc and x

    ang = _Atan2(y - cy, x - cx)

    a.x = cx + d * Cos(ang + _D2R(degAng))

    a.y = cy + d * Sin(ang + _D2R(degAng))

End Sub