form1.vb

Windows mobile 图形编程例子

Public Class Form1

    Protected backBuffer As Bitmap
    Protected displayImage As Image
    Private transparencyValue As Byte = 0
    Private WithEvents blendTimer As Timer

    Public Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        ' Load the image to use with the AlphaBlend API.
        Dim path As String = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase)
        displayImage = New Bitmap(path + "\Microsoft_Windows_Mobile_logo.bmp")

        blendTimer = New Timer()
        blendTimer.Interval = 50

        blendTimer.Enabled = True
    End Sub

    Public Sub blendTimer_Tick(ByVal sender As Object, ByVal e As EventArgs) Handles blendTimer.Tick
        transparencyValue += 10
        If transparencyValue = 250 Then
            transparencyValue = 255 ' opaque
            blendTimer.Enabled = False ' stop the timer
        End If

        ' Force a repaint
        Me.Refresh()
    End Sub

    Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
        ' Make this a no-op, to avoid flicker
    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        If Not backBuffer Is Nothing Then
            ' We need a Graphics object on the buffer to get an HDC
            Using gxBuffer As Graphics = Graphics.FromImage(backBuffer)
                ' Since we nop'd OnPaintBackground, take care of it here
                gxBuffer.Clear(Me.BackColor)

                ' AlphaBlend takes two HDC's - one source and one destination.  Here's the source.
                Using gxSrc As Graphics = Graphics.FromImage(displayImage)
                    Dim hdcDst As IntPtr = gxBuffer.GetHdc()
                    Dim hdcSrc As IntPtr = gxSrc.GetHdc()

                    Dim blendFunction As BlendFunction = New BlendFunction()
                    blendFunction.BlendOp = BlendOperation.AC_SRC_OVER   ' Only supported blend operation
                    blendFunction.BlendFlags = BlendFlags.Zero           ' Documentation says put 0 here
                    blendFunction.SourceConstantAlpha = transparencyValue      ' Constant alpha factor
                    blendFunction.AlphaFormat = 0                        ' Don't look for per pixel alpha

                    Dim left As Int32 = Me.Width / 2 - (displayImage.Width / 2)   ' Get x co-or based on bitmap width
                    Dim top As Int32 = 100                                              ' y co-or
                    PlatformAPIs.AlphaBlend(hdcDst, left, top, _
                        displayImage.Width, displayImage.Height, _
                        hdcSrc, 0, 0, _
                        displayImage.Width, displayImage.Height, _
                        blendFunction)

                    gxBuffer.ReleaseHdc(hdcDst)   ' Required cleanup to GetHdc()
                    gxSrc.ReleaseHdc(hdcSrc)       ' Required cleanup to GetHdc()
                End Using
            End Using

            ' Put the final composed image on screen.
            e.Graphics.DrawImage(backBuffer, 0, 0)
        Else
            e.Graphics.Clear(Me.BackColor)
        End If

    End Sub

    Private Sub Form1_Resize(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Resize
        If Not backBuffer Is Nothing Then
            ' dispose of the original one
            backBuffer.Dispose()
        End If

        ' Create a new backbuffer of the correct size
        backBuffer = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height, _
            System.Drawing.Imaging.PixelFormat.Format32bppRgb)
    End Sub
End Class