笔记一：画笔、笔刷认识

pen主要画线（直线、矩形、圆等）

brush主要用于填充

Imports System.Drawing
Imports System.Math
Public Class Form1
    Dim gr As Graphics
    Dim pen1 As New System.Drawing.Pen(Color.Black,3)
    Dim bp As System.Drawing.Bitmap

    Const pi As Single = 3.14159

    Private Sub Button1_Click(sender As Object,e As EventArgs) Handles Button1.Click
        PictureBox1.Refresh()
        pen1.DashStyle = drawing2d.DashStyle.Dot
        pen1.Color = Color.Blue
        gr = PictureBox1.CreateGraphics
        gr.DrawLine(pen1,100,300)

        '画椭圆
        pen1.DashStyle = drawing2d.DashStyle.DashDotDot '重设线型
        pen1.Color = Color.BlueViolet
        gr.DrawEllipse(pen1,10,200,200)
        gr.dispose()
    End Sub

    
    Private Sub Button2_Click(sender As Object,e As EventArgs) Handles Button2.Click
        PictureBox1.Refresh()
        pen1.Color = Color.Green
        pen1.DashStyle = drawing2d.DashStyle.Dot
        pen1.Width = 1

        Dim x1,y1,x2,y2,x3,y3,x4,y4,x5,y5,r,s,t,u As Single
        For a As Single = 0 To 2 * pi Step pi / 120
            x1 = 240 + 30 * Cos(a)
            y1 = 160 + 15 * Sin(a)
            r = 60 * (1 + 1 / 6 * Sin(3 * a))
            s = 80 * (1 + 1 / 6 * Sin(4 * a))
            t = 100 * (1 + 1 / 6 * Sin(5 * a))
            u = 140 * (1 + 1 / 8 * Sin(6 * a))
            x2 = r * Cos(a + pi / 20) + 240
            y2 = r * Sin(a + pi / 20) + 160
            x3 = s * Cos(a) + 240
            y3 = s * Sin(a) + 160
            x4 = t * Cos(a + pi / 20) + 240
            y4 = t * Sin(a + pi / 20) + 160
            x5 = 1.5 * u * Cos(a) + 240
            y5 = u * Sin(a) + 160
            pen1.Color = Color.Red
            gr = PictureBox1.CreateGraphics
            gr.DrawLine(pen1,x1,y2)
            pen1.Color = Color.BlueViolet
            gr.DrawLine(pen1,y3)
            pen1.Color = Color.Red
            gr.DrawLine(pen1,y4)
            pen1.Color = Color.GreenYellow
            gr.DrawLine(pen1,y5)
        Next
    End Sub

    Private Sub Button3_Click(sender As Object,e As EventArgs) Handles Button3.Click
        'HatchBrush()        阴影笔刷
        'LinearGradientBrush   线性渐变笔刷 
        'SolidBrush          单色笔刷
        'TextureBrush       纹理笔刷
        'PathGradientBrus  渐变色填充

        '阴影笔刷（十字图案）
        Dim br1 As System.Drawing.drawing2d.HatchBrush
        br1 = New System.Drawing.drawing2d.HatchBrush(drawing2d.HatchStyle.Cross,Color.Red,Color.Black)
        gr = PictureBox1.CreateGraphics
        gr.FillEllipse(br1,250,150)
        br1.dispose()

        '线性渐变笔刷
        Dim br2 As System.Drawing.drawing2d.LinearGradientBrush
        Dim p1 As New Point(140,140) 'p1,p2控制渐变频率
        Dim p2 As New Point(160,170)
        br2 = New System.Drawing.drawing2d.LinearGradientBrush(p1,p2,Color.Black)
        gr.FillRectangle(br2,150,50)
        br2.dispose()

        '渐变色填充（不规则或多边形）
        Dim p(2) As Point '建立path
        p(0).X = 0 : p(0).Y = 0
        p(1).X = 20 : p(1).Y = 10
        p(2).X = 11 : p(2).Y = 22
        Dim br3 As System.Drawing.drawing2d.PathGradientBrush
        br3 = New System.Drawing.drawing2d.PathGradientBrush(p,Drawing.drawing2d.WrapMode.Tile)
        br3.CenterColor = Color.Blue  '中心色
        br3.SurroundColors = New Color() {Color.Red,Color.Green,Color.Black} '边沿色对应各点数，除非是圆（一种色）
        br3.CenterPoint = New Point(11,15) '指定中心点
        gr.FillEllipse(br3,100)
        br3.dispose()
    End Sub

    Private Sub Button4_Click(sender As Object,e As EventArgs) Handles Button4.Click
        PictureBox1.Refresh()
    End Sub
End Class

仔细一看上面PathGradientBrush笔刷，发现每个不规则封闭图形中好像有“间距”，

我们放大看一下，原来，并不是间距，而是以这个不规则图外沿作为一个矩形，“平辅”到整个图形中。

添加一下辅助线，就可以清晰看出它成图的原因了：