笔记二：画形状

Graphics用来绘图。

用draw来划线。vb.net没有画点的功能。

可以画直接、矩形、椭圆、Bezier、弧、饼（封闭的弧线）。

要注意的是：弧、饼用的是度数（不是弧度），且是顺时间转的角度。

Imports System.Drawing
Imports System.Math
Public Class Form1
    Const pi As Double = 3.14159

    '画点（用一个像素的矩形或两个像素的直接来模拟
    Private Sub Button1_Click(sender As Object,e As EventArgs) Handles Button1.Click
        Dim gr As Graphics = PictureBox1.CreateGraphics
        Dim j As Int32 = 50
        For i As Int32 = 10 To 150
            gr.DrawLine(Pens.Red,i,j,i + 1,j + 1)
            j += 1
        Next
    End Sub

    '用直线构成图
    Private Sub Button2_Click(sender As Object,e As EventArgs) Handles Button2.Click
        PictureBox1.Refresh() '清除

        Dim gr As Graphics = PictureBox1.CreateGraphics
        Dim x1,y1,x2,y2,d As Short '起点终点、基准距离
        Dim b,c As Double '真实距离

        d = 60
        For a = 0 To 2 * pi Step pi / 360
            b = d * (1 + 1 / 4 * Cos(12 * a))
            c = b * (1 + Sin(4 * a))
            x1 = 150 + Int(c * Cos(a))  '（150，180）中心点
            y1 = 180 + Int(c * Sin(a))
            x2 = 150 + Int(c * Cos(a + pi / 5))
            y2 = 180 + Int(c * Sin(a + pi / 5))
            gr.DrawLine(Pens.BlueViolet,x1,y2)
        Next
    End Sub

    '椭圆或圆
    Private Sub Button3_Click(sender As Object,e As EventArgs) Handles Button3.Click
        PictureBox1.Refresh()
        Dim gr As Graphics = PictureBox1.CreateGraphics
        gr.DrawEllipse(Pens.Red,New Rectangle(0,100,80))
        gr.DrawEllipse(Pens.Aqua,New Rectangle(120,120,80,80))
    End Sub

    '椭圆弧  或圆弧 (是对上面椭圆的部分提取）
    '注意：开始和结束角度是以度为单位，且顺时针方向，下面是从30度到120度
    Private Sub Button4_Click(sender As Object,e As EventArgs) Handles Button4.Click
        PictureBox1.Refresh()
        Dim gr As Graphics = PictureBox1.CreateGraphics
        gr.DrawArc(Pens.Red,New Rectangle(20,20,150,200),30,120)
    End Sub

    '封闭椭圆弧线，即饼图
    '参数与arc同，只是成图时是封闭的
    Private Sub Button5_Click(sender As Object,e As EventArgs) Handles Button5.Click
        PictureBox1.Refresh()
        Dim gr As Graphics = PictureBox1.CreateGraphics
        gr.DrawPie(Pens.Red,120)
    End Sub

    '贝赛尔曲线 Bezier
    '它由四个点：起点、两个中间点（控制）、终点 组成
    Private Sub Button6_Click(sender As Object,e As EventArgs) Handles Button6.Click
        PictureBox1.Refresh()
        Dim gr As Graphics = PictureBox1.CreateGraphics
        gr.DrawBezier(Pens.Brown,10,140,40,240,200,270)
        gr.DrawRectangle(Pens.Red,New Rectangle(200,170))
    End Sub

    '多边形--不规则形状
    '由多个点来决定，多个点用Points()数组来表达
    Private Sub Button7_Click(sender As Object,e As EventArgs) Handles Button7.Click
        PictureBox1.Refresh()
        Dim gr As Graphics = PictureBox1.CreateGraphics
        Dim p(2) As System.Drawing.Point

        p(0).X = 30 : p(0).Y = 30
        p(1).X = 100 : p(1).Y = 100
        p(2).X = 50 : p(2).Y = 250
        gr.DrawPolygon(Pens.DarkGreen,p)
    End Sub
End Class

（编辑：李大同）

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