(08-23-2022, 04:07 PM)dcromley Wrote: James,

Solving the equation for x is the easy part:
x^2/a^2 + y^2/b^2 = 1
x^2/a^2 = 1 - y^2/b^2
x^2 = (1 - y^2/b^2 )*a^2
x = +sqr((1 - y^2/b^2 )*a^2)
and
x = -sqr((1 - y^2/b^2 )*a^2)
if I haven't made a mistake.

But you can use CIRCLE to draw ellipses.  Or, if you are into self-flagellation, there are algorithms using PSET.

Here is a start using CIRCLE (the ASPECT parameter!):

(08-23-2022, 04:54 PM)bplus Wrote: If you need tilted ones I have that too (https://staging.qb64phoenix.com/showthread.php?tid=272&pid=1204#pid1204)  here are filled ellipsii

Code: (Select All)

_Title "Fill Ellipse Demo" ' b+ 2022-08-23
Screen _NewImage(800, 600, 32)
_ScreenMove 200, 50
Do
    fEllipse Rnd * _Width, Rnd * _Height, Rnd * 100, Rnd * 100, _RGB32(Rnd * 255, Rnd * 255, Rnd * 255, Rnd * 255)
    _Limit 30
Loop


Sub fEllipse (CX As Long, CY As Long, xr As Long, yr As Long, C As _Unsigned Long)
    If xr = 0 Or yr = 0 Then Exit Sub
    Dim h2 As _Integer64, w2 As _Integer64, h2w2 As _Integer64
    Dim x As Long, y As Long
    w2 = xr * xr: h2 = yr * yr: h2w2 = h2 * w2
    Line (CX - xr, CY)-(CX + xr, CY), C, BF
    Do While y < yr
        y = y + 1
        x = Sqr((h2w2 - y * y * w2) \ h2)
        Line (CX - x, CY + y)-(CX + x, CY + y), C, BF
        Line (CX - x, CY - y)-(CX + x, CY - y), C, BF
    Loop
End Sub

xr = xradius  yr = yradius don't have to guess with fractions that Circle uses.

(08-23-2022, 05:37 PM)James D Jarvis Wrote: my weak ellipse drawing for you if you don't want to use circle.  My pset method is missing something because I do not recall the math in that area where sqr() can't be called. Bplus is better here. The method using draw actually comes out decent enough.

Code: (Select All)

'badellipse
Screen _NewImage(800, 600, 256)
'pset ellipse
ex = 200
ey = 300
a = 160
b = 50
For y = 0 To 100 Step 0.2
    n = (1 - y ^ 2 / b ^ 2) * a ^ 2 'have to calculate outside sqr() to avoid math error
    If n > 0 Then
        x = Sqr(n)
        PSet (x + ex, y + ey), 15
        PSet (ex - x, y + ey), 15
        PSet (ex - x, ey - y), 15
        PSet (x + ex, ey - y), 15
    End If
Next y


'draw ellipse
ex = 600
ey = 300
a = 160
b = 50
Draw "bm" + Str$(ex) + "," + Str$(ey)
For y = 0 To 100 Step 1 'using larger steps than earlier because draw is slower but laying down line segments
    n = (1 - y ^ 2 / b ^ 2) * a ^ 2
    If n > 0 Then
        x = Sqr(n)
        If y < 1 Then Draw "bm" + Str$(x + ex) + "," + Str$(y + ey)
        Draw "m" + Str$(x + ex) + "," + Str$(y + ey)
    End If
Next y
For y = 100 To 0 Step -1
    n = (1 - y ^ 2 / b ^ 2) * a ^ 2
    If n > 0 Then
        x = Sqr(n)
        If y > 99 Then Draw "bm" + Str$(x + ex) + "," + Str$(y + ey)
        Draw "m" + Str$(ex - x) + "," + Str$(y + ey)
    End If
Next y
For y = 0 To 100 Step 1
    n = (1 - y ^ 2 / b ^ 2) * a ^ 2
    If n > 0 Then
        x = Sqr(n)
        If y < 0 Then Draw "bm" + Str$(x + ex) + "," + Str$(y + ey)
        Draw "m" + Str$(ex - x) + "," + Str$(ey - y)
    End If
Next y
For y = 100 To 0 Step -1
    n = (1 - y ^ 2 / b ^ 2) * a ^ 2
    If n > 0 Then
        x = Sqr(n)
        If y > 99 Then Draw "bm" + Str$(x + ex) + "," + Str$(y + ey)
        Draw "m" + Str$(x + ex) + "," + Str$(ey - y)
    End If
Next y