怎么用api画圆，并用弦截断，两块涂上不同的颜色

如何用api画圆，并用弦截断，两块涂上不同的颜色？


就是用vb画出这样的图形？

不是在form上面绘图，我是写一个控件，也就是在usercontrol上面绘制，怎么办呢？

[解决办法]

VB code

'form中添加一个pictureBox，一个commandButtonPrivate Declare Function ExtFloodFill Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long, ByVal wFillType As Long) As LongPrivate Sub Command1_Click()Dim w As DoubleDim h As DoubleDim a As Double, b As DoubleDim r As DoubleDim t1 As DoubleDim t2 As DoubleDim x1 As Double, y1 As DoubleDim x2 As Double, y2 As Double   With Picture1     .AutoRedraw = True     .ScaleMode = vbPixels     .FillStyle = vbFSSolid          w = Picture1.ScaleWidth     h = Picture1.ScaleHeight     a = w / 2     b = h / 2     r = h / 4     t1 = 0     t2 = 3 * PI / 2          '弦两点的坐标，不知道算法对了没     If t1 > PI Then        x1 = a + Cos(t1) * r        y1 = b + Sin(t1) * r     Else        x1 = a + Cos(t1) * r        y1 = b - Sin(t1) * r     End If          If t1 > PI Then        x2 = a + Cos(t2) * r        y2 = b + Sin(t2) * r    Else        x2 = a + Cos(t2) * r        y2 = b - Sin(t2) * r    End If          Picture1.Circle (a, b), r, vbBlue, t1, t2     Picture1.Circle (a, b), r, vbRed, t2, t1     Picture1.Line (x1, y1)-(x2, y2), vbRed         Dim x3 As Double, y3 As Double     '欲填充区域内的一点，我是通过MouseDown事件中随便取一点     '如果有算法能计算出一个属于目标区域的点坐标，那最好了     x3 = 283     y3 = 210     .FillColor = RGB(Int(Rnd * 255), Int(Rnd * 255), Int(Rnd * 255))     ExtFloodFill .hdc, x3, y3, .Point(x3, y3), 1          x3 = 244     y3 = 158     .FillColor = RGB(Int(Rnd * 255), Int(Rnd * 255), Int(Rnd * 255))     ExtFloodFill .hdc, x3, y3, .Point(x3, y3), 1    End WithEnd Sub
[解决办法]
上面  If t1 > PI Then
       x2 = a + Cos(t2) * r
       y2 = b + Sin(t2) * r
   Else
       x2 = a + Cos(t2) * r
       y2 = b - Sin(t2) * r
   End If
写错了（好像弦交点坐标也算错了）
if t2 >PI

另：常量定义

Const PI = 3.14