如何用api画圆，并用弦截断，两块涂上不同的颜色？

[yardloun]

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？

[jiashie]

API：
FloodFill
ExtFloodFill

[yardloun]

楼上，请问具体怎么操作呢？很不懂那个封闭区域是怎么识别出来的，它怎么确定哪些是封闭的？

[贝隆]

直接使用Line方法绘制，算好两个点绘制

[yardloun]

很希望2楼能给出一个例子哈，例子中用到的数值大小随便定，谢谢哈

[jiashie]

'form中添加一个pictureBox，一个commandButton
Private 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 Long

Private Sub Command1_Click()
Dim w As Double
Dim h As Double
Dim a As Double, b As Double
Dim r As Double
Dim t1 As Double
Dim t2 As Double
Dim x1 As Double, y1 As Double
Dim 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 With
End Sub

[jiashie]

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

[jiashie]

哎，几何没学好。。。