Почему процедура заливает весь PictureBox а не только окружность

Sub BackgroundCircularGradient(pic As PictureBox, _
                                ByVal startColor As Long, _
                                ByVal endColor As Long, _
                                Optional ByVal numSteps As Integer = 256, _
                                Optional ByVal xc As Single = -1, _
                                Optional ByVal yc As Single = -1)
    
    Dim startRed As Integer, startGreen As Integer, startBlue As Integer
    Dim deltaRed As Integer, deltaGreen As Integer, deltaBlue As Integer
    Dim R As Single, dr As Single
    Dim stp As Long
    
    Dim saveFillColor As Long
    Dim saveFillStyle As Long
    
    ' Evaluate the coordinates of the center if omitted.
    If xc = -1 And yc = -1 Then
        xc = pic.ScaleWidth / 2
        yc = pic.ScaleHeight / 2
    End If
    
    ' The radius of the circle is equal to the distance from the farthest corner
    If xc < pic.ScaleWidth / 2 Then
        If yc < pic.ScaleHeight / 2 Then
            R = Sqr((pic.ScaleWidth - xc) ^ 2 + (pic.ScaleHeight - yc) ^ 2)
        Else
            R = Sqr((pic.ScaleWidth - xc) ^ 2 + yc ^ 2)
        End If
    Else
        If yc < pic.ScaleHeight / 2 Then
            R = Sqr(xc ^ 2 + (pic.ScaleHeight - yc) ^ 2)
        Else
            R = Sqr(xc ^ 2 + yc ^ 2)
        End If
    End If
    
    ' Split the start color into its RGB components
    startRed = startColor And &HFF
    startGreen = (startColor And &HFF00&) \ 256
    startBlue = (startColor And &HFF0000) \ 65536
    ' Split the end color into its RGB components
    deltaRed = (endColor And &HFF&) - startRed
    deltaGreen = (endColor And &HFF00&) \ 256 - startGreen
    deltaBlue = (endColor And &HFF0000) \ 65536 - startBlue
    
    RealizePalette pic.hdc
    
    ' Eval the delta of the radius at each step
    dr = R / numSteps
    
    ' Remember current fill settings.
    saveFillColor = pic.FillColor
    saveFillStyle = pic.FillStyle
    ' enfore solid filling
    pic.FillStyle = vbSolid
    
    ' Draw all circles, going from the outside in.
    For stp = 0 To numSteps - 1
        pic.FillColor = RGB(startRed + (deltaRed * stp) \ numSteps, _
            startGreen + (deltaGreen * stp) \ numSteps, _
            startBlue + (deltaBlue * stp) \ numSteps)
        pic.Circle (xc, yc), R, pic.FillColor
        R = R - dr
    Next
    
    ' Restore original settings.
    pic.FillColor = saveFillColor
    pic.FillStyle = saveFillStyle
End Sub