Вы можете приблизить кольцо с большим количеством трапеций и использовать разные цвета заливки для каждого прямоугольника.
Imports System.Drawing.Drawing2D
Public Class Form1
Private Sub Form1_Paint(sender As Object, e As PaintEventArgs) Handles MyBase.Paint
Dim centre = New PointF(160, 140)
Dim r1 = 100
Dim r2 = 105
Dim colourStart = 90 * Math.PI / 180
Dim col1 As Color
col1 = Color.FromArgb(0, 0, 0)
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias
Using br As New SolidBrush(col1)
Dim nSteps = 180
Dim aInc = 2 * Math.PI / nSteps
For i = 0 To nSteps - 1
Dim a = i * aInc
Dim t1 = a
Dim t2 = a + aInc
Dim p1 = New PointF(CSng(r2 * Math.Cos(t1)) + centre.X, CSng(r2 * Math.Sin(t1)) + centre.Y)
Dim p2 = New PointF(CSng(r1 * Math.Cos(t1)) + centre.X, CSng(r1 * Math.Sin(t1)) + centre.Y)
Dim p3 = New PointF(CSng(r1 * Math.Cos(t2)) + centre.X, CSng(r1 * Math.Sin(t2)) + centre.Y)
Dim p4 = New PointF(CSng(r2 * Math.Cos(t2)) + centre.X, CSng(r2 * Math.Sin(t2)) + centre.Y)
Dim pts = {p1, p2, p3, p4}
col1 = HSL2RGB(a + colourStart, 1, 0.5)
br.Color = col1
e.Graphics.FillPolygon(br, pts)
Next
End Using
End Sub
' HSL2RGB from https://dotnetfiddle.net/aORkec (with translation and bugfix).
''' <summary>
''' Convert HSL to RGB.
''' </summary>
''' <param name="h">Hue 0..2pi</param>
''' <param name="s">Saturation 0..1</param>
''' <param name="l">Lightness 0..1</param>
''' <returns>RGB color.</returns>
<DebuggerHidden>
Function HSL2RGB(h As Double, s As Double, l As Double) As Color
If h > 2 * Math.PI Then h -= 2 * Math.PI
If h < 0 Then h += 2 * Math.PI
h = h / (2 * Math.PI)
Dim v As Double
Dim r, g, b As Double
r = l
g = l
b = l
v = If(l <= 0.5, l * (1.0 + s), l + s - l * s)
If (v > 0) Then
Dim m As Double
Dim sv As Double
Dim sextant As Integer
Dim fract, vsf, mid1, mid2 As Double
m = l + l - v
sv = (v - m) / v
h *= 6.0
sextant = CInt(Math.Floor(h))
fract = h - sextant
vsf = v * sv * fract
mid1 = m + vsf
mid2 = v - vsf
Select Case sextant
Case 0, 6
r = v
g = mid1
b = m
Case 1
r = mid2
g = v
b = m
Case 2
r = m
g = v
b = mid1
Case 3
r = m
g = mid2
b = v
Case 4
r = mid1
g = m
b = v
Case 5
r = v
g = m
b = mid2
End Select
End If
Return Color.FromArgb(Convert.ToByte(r * 255.0F), Convert.ToByte(g * 255.0F), Convert.ToByte(b * 255.0F))
End Function
End Class
Результат:
Лучших результатов, вероятно, можно достичь, используя Bru sh, который позволяет градиент цвета в правильном направлении для каждого прямоугольника.
Также возможно сделать круг из кольцевого секторы, которые дают точные границы вместо прямых краев трапеций:
Function Rad2Deg(x As Double) As Single
Return Convert.ToSingle(x * 180 / Math.PI)
End Function
Private Sub Form1_Paint(sender As Object, e As PaintEventArgs) Handles MyBase.Paint
Dim centreF = New PointF(160, 140)
Dim centre = New Point(CInt(centreF.X), CInt(centreF.Y))
Dim r1 = 100
Dim r2 = 105
Dim boundingRectInner = New Rectangle(-r1, -r1, r1 * 2, r1 * 2)
boundingRectInner.Offset(centre)
Dim boundingrectOuter = New Rectangle(-r2, -r2, r2 * 2, r2 * 2)
boundingrectOuter.Offset(centre)
Dim colourStart = 90 * Math.PI / 180
Dim col1 As Color
col1 = Color.FromArgb(0, 0, 0)
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias
Using br As New SolidBrush(col1)
Dim nSteps = 12
Dim aInc = 2 * Math.PI / nSteps
Dim sweepAngle = Rad2Deg(aInc)
For i = 0 To nSteps - 1
Dim a = i * aInc
Dim t1 = a
Dim t2 = a + aInc
Dim p3 = New PointF(CSng(r1 * Math.Cos(t2)) + centreF.X, CSng(r1 * Math.Sin(t2)) + centreF.Y)
Dim p4 = New PointF(CSng(r2 * Math.Cos(t2)) + centreF.X, CSng(r2 * Math.Sin(t2)) + centreF.Y)
Using gp As New GraphicsPath()
gp.AddArc(boundingRectInner, Rad2Deg(a), sweepAngle)
gp.AddLine(p3, p4)
gp.AddArc(boundingrectOuter, Rad2Deg(a + aInc), -sweepAngle)
gp.CloseFigure()
col1 = HSL2RGB(a + colourStart, 1, 0.5)
br.Color = col1
e.Graphics.FillPath(br, gp)
End Using
Next
End Using
End Sub
Обратите внимание на меньшее количество шагов, поэтому цветов меньше, но края по-прежнему имеют круг:
