need help with filled circle

check this out...sometimes it draws where it shouldn't...

Hello,

I think this function should solve it:

VB Code:

Public Sub Glow(X As Single, Y As Single, Brightness As Double)
  Dim xFrom As Single, xTo As Single, yFrom As Single, yTo As Single
  Dim xx As Single, yy As Single, yDiff As Single
'    TempRadius = Radius
'    For TempRadius = 1 To Radius
'        For Angle = 0 To PiTimes2 Step PiTimes2 / (TempRadius * 2 * Pi)
'            BlendDIBPixel Round2(X + Sin(Angle) * TempRadius), Round2(Y + Cos(Angle) * TempRadius), 200, 100, 50, Brightness
'        Next
'    Next
  yFrom = Y - Radius
  yTo = Y + Radius
 
  For yy = yFrom To yTo
    yDiff = (yy - Y) / Radius
    xTo = X + Sqr(1 - yDiff * yDiff) * Radius
    xFrom = 2 * X - xTo
    For xx = xFrom To xTo
      BlendDIBPixel xx, yy, 200, 100, 50, Brightness
    Next xx
  Next yy
  
End Sub

The commented part is your function.
There's one strange thing though: initially the circle is drawn as two half circles at the left and right edge. I didn't figure out yet why.

While filling shapes, most algorithms are based on the idea that a shape is built of scanlines. Just color the pixels in the scanline which fall within the shape. (hence the for xx statement).

Coincidentally or not: I'm busy with shape filling as well. They're just straight polygons (eventually with edges). I'm using a fill algorithm which keeps track of the collection of edges which together form the polygon. There's a slight rounding problem however. At one side there are blank pixels inside the polygon, and at the other side they are outside the polygon. I'm also drawing the outline, so it's quite disturbing if you want to do it really good...