Ellipse trouble

[James D Jarvis]

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