CCircle类

在项目中添加CCircle类,它是CGElement类的派生类。CCircle类也要继承CGElement类的3个属性和DrawSettings方法。除此之外,CCircle类还要提供确定圆本身所需要的圆心和圆上一点两个属性,另外还有一个Radius属性,它是只读的,根据圆心坐标和圆上一点的坐标,可以计算出半径Radius。与CLine类一样,CCircle也提供了3个构造函数。其中,根据两个给定的点构造一个圆是最常用的。

由于计算半径Radius时要用到数学药数,所以需要导入System.Math名字空间。但是,在VC#.NET中没有该名字空间,可以直接调用Math类。

code.vb.net 
'圆类
Imports System.Math
Public Class CCircle
    Inherits CGElement
    Private m_Center, m_PCircle As PointF
    '圆心属性
    Public Property Center() As PointF
        Get
            Return m_Center
        End Get
        Set(By Val Value As PointF)
            m_Center=Value
        End Set
    End Property
    '圆上一点属性
    Public Property PCircle() As PointF
        Get
            Return m PCircle
        End Get
        Set(By Val Value As PointF)
            m PCircle = Value
        End Set"
    End Property
    '半径属性,只读
    Public ReadOnly Property Radius( As Single
        Get
            Dim r As Single
            r= distPtoP(m_Center,m_pCircle)
            Return r
        End Get
    End Property
    '无参构造函数
    Public Sub New()
        Init()
    End Sub
    '构造函数,用已知的两个点构造圆
    Public Sub New(By Val pCenter As PointF, ByVal pCircle As PointF)
        Init()
        m_Center = pCenter
        m_PCircle = pCircle
    End Sub
    '构造函数,用已知的圆构造圆
    Public Sub New(By Val aCircle As CCircle)
        With aCircle
            m Center =.Center
            m PCircle =.PCircle
        End With
    End Sub
    '初始化圆
    Private Shadows Sub Init()
        MyBase.Init()
        With m_Center
            X=0
            .Y=0
        End With
        m_ PCircle = m_Center
    End Sub"
    '计算点与点之间的距离
    Public Function DistPtoP(ByVal p1 As PointF, ByVal p2 As PointF) As Single
        Dim dx, dy As Single
        dx = p2.X- p1.X
        dy = p2.Y - p1.Y
        Return Sqrt((dx *dx)+(dy * dy))
    End Function
End Class

在CCircle类中重写基类的Draw方法,根据不同的绘图模式绘圆。在绘图之前,同样需要将圆心和圆上一点的坐标从通用坐标转换为页面坐标。像素模式下,设备坐标的大小与该页面坐标相同。后面绘图的过程也基本上与绘直线段相同,但是需要选一把空刷子到绘图环境中,否则绘出的是黑色的圆形区域,该操作用GetStockObject断数实现,需要从Win32AP类中调用它。绘圆使用的是Ellipse函数。

code.vb.net 
'绘圆
Public Overrides Sub Draw(By Val g As Graphics, By Val aDrawMode As geDrawMode)
    Dim aPen, oldP As Long
    '将控制点的坐标转换为页面坐标"
    Dim ec As PointF = WorldtoPage(m_Center)
    Dim ep As PointF = WorldtoPage(m_ PCircle)
    '获取绘图环境的句柄
    Dim hdc As IntPtr
    hdc =g.GetHdc()
    '设置画笔参数
    Dim penPara As Integer() = DrawSettings(hdc, aDrawMode)
    '创建画笔
    aPen = Win32APL.CreatePen(penPara(0),penPara(1),penPara(2))
    '把画笔选入绘图环境,并返回原来的画笔
    oldP = Win32API.SelectObject(hdc, aPen)
    '把空刷子选入绘图环境
    Win32APL.SelectObject(hdc, Win32API.GetStockObject(5))
    '绘圆
    Win32API.Ellipse(hdc, ec.X- Radius,ec.Y+Radius,ec.X+ Radius, ec.Y - Radius)
    '把原来的画笔选入绘图环境
    Win32API.SelectObject(hdc, oldP)
    '删除新创建的画笔
    Win32API.DeleteObject(aPen)
    '释放绘图环境句柄
    g.ReleaseHdc(hdc)
End Sub