vb.net 教程 5-9 屏幕范围内取色- VB

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屏幕范围内取色
在本博客《vb：Cg色彩精灵》系列中，我们在vb6中使用Api函数对屏幕进行取色，在vb.net中，我们可以有更简单的方法完成此项工作。

延续使用我们在《颜色》中的窗口界面，增加两个控件：
btnPick Button
lblLocation Label

窗体级的变量
isPick：标识是否开始取色
bmp：不可见的bitmap，保存了当前屏幕的截图

Dim isPick As Boolean
Dim bmp As Bitmap

鼠标左键按下的时候我们要做的工作：
1、设置按下鼠标左键时，isPick为真，标识开始取色
2、将屏幕截图保存在bmp中
3、将鼠标光标设置为十字样式

Private Sub btnPick_MouseDown(sender As Object, e As MouseEventArgs) Handles btnPick.MouseDown
If e.Button = MouseButtons.Left Then
isPick = True
Dim Scr As Screen = Screen.PrimaryScreen
Dim recSc As Rectangle = Scr.Bounds
bmp = New Bitmap(recSc.Width, recSc.Height)
Dim g As Graphics = Graphics.FromImage(bmp)

g.CopyFromScreen(New Point(0, 0), New Point(0, 0), New Size(recSc.Width, recSc.Height))

Me.Cursor = Cursors.Cross
End If
End Sub

鼠标移动的时候我们要做的工作
1、获得鼠标坐标位置
2、将鼠标坐标转换为屏幕坐标,通过控件的PointToScreen()方法完成
3、对bmp坐标点取色，通过GetPixel()方法完成
4、附加对颜色的RGB值做了简单分析

Private Sub btnPick_MouseMove(sender As Object, e As MouseEventArgs) Handles btnPick.MouseMove
Dim x, y As Integer
Dim p As Point = New Point(e.X, e.Y)
Dim colorPoint As Color
Dim r, g, b As Byte

If isPick = True Then
x = btnPick.PointToScreen(p).X
y = btnPick.PointToScreen(p).Y
lblLocation.Text = "x:" & x & " y:" & y
colorPoint = bmp.GetPixel(x, y)

picPalette.BackColor = colorPoint
r = colorPoint.R
g = colorPoint.G
b = colorPoint.B

hsbRed.Value = r
hsbGreen.Value = g
hsbBlue.Value = b

lblRed.Text = r.ToString
lblGreen.Text = g.ToString
lblBlue.Text = b.ToString

Call toWebColor()
End If
End Sub