2024年2月21日发(作者：)

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利用VB捕捉并保存屏幕图像

大家知道在VB下利用API函数Bitblt可以将屏幕或者窗口上的图象拷贝到VB中的PictureBox对象中,但是如果简单的利用PictureBox的SavePicture函数来保存图象，会发现什么也保存不了。这篇文章就是介绍如何捕获并利用Windows下的OLE API函数保存图象。

首先来看源程序，首先建立一个新的工程文件，然后在Form1中加入5个CommandButton对象和一个PictureBox对象，然后在Form1中加入以下代码：

Option Explicit

Option Base 0

Private Type PALETTEENTRY

peRed As Byte

peGreen As Byte

peBlue As Byte

peFlags As Byte

End Type

Private Type LOGPALETTE

palVersion As Integer

palNumEntries As Integer

palPalEntry(255) As PALETTEENTRY

End Type

Private Type GUID

Data1 As Long

Data2 As Integer

Data3 As Integer

Data4(7) As Byte

End Type

Private Const RASTERCAPS As Long = 38

Private Const RC_PALETTE As Long = &H100

Private Const SIZEPALETTE As Long = 104

Private Type RECT

Left As Long

Top As Long

Right As Long

Bottom As Long

End Type

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Private Declare Function CreateCompatibleDC Lib "GDI32" (ByVal hDC As

Long) As Long

Private Declare Function CreateCompatibleBitmap Lib "GDI32" (ByVal hDC

As Long, _

ByVal nWidth As Long, ByVal nHeight As Long) As Long

Private Declare Function GetDeviceCaps Lib "GDI32" (ByVal hDC As Long,

ByVal _

iCapabilitiy As Long) As Long

Private Declare Function GetSystemPaletteEntries Lib "GDI32" (ByVal hDC

As Long, _

ByVal wStartIndex As Long, ByVal wNumEntries As Long,

lpPaletteEntries _

As PALETTEENTRY) As Long

Private Declare Function CreatePalette Lib "GDI32" (lpLogPalette As

LOGPALETTE) _

As Long

Private Declare Function SelectObject Lib "GDI32" (ByVal hDC As Long,

ByVal hObject _

As Long) As Long

Private Declare Function BitBlt Lib "GDI32" (ByVal hDCDest As Long, ByVal

XDest As _

Long, ByVal YDest As Long, ByVal nWidth As Long, ByVal nHeight

As Long, _

ByVal hDCSrc As Long, ByVal XSrc As Long, ByVal YSrc As Long, ByVal

dwRop _

As Long) As Long

Private Declare Function DeleteDC Lib "GDI32" (ByVal hDC As Long) As Long

Private Declare Function GetForegroundWindow Lib "USER32" () As Long

Private Declare Function SelectPalette Lib "GDI32" (ByVal hDC As Long,

ByVal hPalette _

As Long, ByVal bForceBackground As Long) As Long

Private Declare Function RealizePalette Lib "GDI32" (ByVal hDC As Long)

As Long

Private Declare Function GetWindowDC Lib "USER32" (ByVal hWnd As Long)

As Long

Private Declare Function GetDC Lib "USER32" (ByVal hWnd As Long) As Long

Private Declare Function GetWindowRect Lib "USER32" (ByVal hWnd As Long,

lpRect As _

RECT) As Long

Private Declare Function ReleaseDC Lib "USER32" (ByVal hWnd As Long, ByVal

hDC As _

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Long) As Long

Private Declare Function GetDesktopWindow Lib "USER32" () As Long

Private Type PicBmp

Size As Long

Type As Long

hBmp As Long

hPal As Long

Reserved As Long

End Type

Private Declare Function OleCreatePictureIndirect Lib ""

(PicDesc As _

PicBmp, RefIID As GUID, ByVal fPictureOwnsHandle As Long, IPic

As IPicture) As Long

'捕捉整个屏幕

Private Sub Command1_Click()

Set e = CaptureScreen()

End Sub

'在两秒钟后捕捉当前的活动窗口

Private Sub Command2_Click()

MsgBox "当你关闭这个对话框两秒钟之后程序会捕捉处于活动状态的窗口."

'等待两秒钟

Dim EndTime As Date

EndTime = DateAdd("s", 2, Now)

Do Until Now > EndTime

DoEvents

Loop

Set e = CaptureActiveWindow()

us

End Sub

Private Sub Command3_Click()

Set e = Nothing

End Sub

Public Function CreateBitmapPicture(ByVal hBmp As Long, ByVal hPal As

Long) As Picture

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Dim r As Long

Dim Pic As PicBmp

Dim IPic As IPicture

Dim IID_IDispatch As GUID

'填充IDispatch界面

With IID_IDispatch

.Data1 = &H20400

.Data4(0) = &HC0

.Data4(7) = &H46

End With

'填充Pic

With Pic

.Size = Len(Pic) ' Pic结构长度

.Type = vbPicTypeBitmap ' 图象类型

.hBmp = hBmp ' 位图句柄

.hPal = hPal ' 调色板句柄

End With

'建立Picture图象

r = OleCreatePictureIndirect(Pic, IID_IDispatch, 1, IPic)

'返回Picture对象

Set CreateBitmapPicture = IPic

End Function

Public Function CaptureWindow(ByVal hWndSrc As Long, ByVal Client As

Boolean, ByVal _

LeftSrc As Long, ByVal TopSrc As Long, ByVal WidthSrc As Long, ByVal

HeightSrc _

As Long) As Picture

Dim hDCMemory As Long

Dim hBmp As Long

Dim hBmpPrev As Long

Dim r As Long

Dim hDCSrc As Long

Dim hPal As Long

Dim hPalPrev As Long

Dim RasterCapsScrn As Long

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Dim HasPaletteScrn As Long

Dim PaletteSizeScrn As Long

Dim LogPal As LOGPALETTE

If Client Then

hDCSrc = GetDC(hWndSrc)

Else

hDCSrc = GetWindowDC(hWndSrc)

End If

hDCMemory = CreateCompatibleDC(hDCSrc)

hBmp = CreateCompatibleBitmap(hDCSrc, WidthSrc, HeightSrc)

hBmpPrev = SelectObject(hDCMemory, hBmp)

'获得屏幕属性

RasterCapsScrn = GetDeviceCaps(hDCSrc, RASTERCAPS)

HasPaletteScrn = RasterCapsScrn And RC_PALETTE

PaletteSizeScrn = GetDeviceCaps(hDCSrc, SIZEPALETTE)

'如果屏幕对象有调色板则获得屏幕调色板

If HasPaletteScrn And (PaletteSizeScrn = 256) Then

'建立屏幕调色板的拷贝

sion = &H300

Entries = 256

r = GetSystemPaletteEntries(hDCSrc, 0, 256,

Entry(0))

hPal = CreatePalette(LogPal)

'将新建立的调色板选如建立的内存绘图句柄中

hPalPrev = SelectPalette(hDCMemory, hPal, 0)

r = RealizePalette(hDCMemory)

End If

'拷贝图象

r = BitBlt(hDCMemory, 0, 0, WidthSrc, HeightSrc, hDCSrc, LeftSrc,

TopSrc, vbSrcCopy)

hBmp = SelectObject(hDCMemory, hBmpPrev)

If HasPaletteScrn And (PaletteSizeScrn = 256) Then

hPal = SelectPalette(hDCMemory, hPalPrev, 0)

End If

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'释放资源

r = DeleteDC(hDCMemory)

r = ReleaseDC(hWndSrc, hDCSrc)

Set CaptureWindow = CreateBitmapPicture(hBmp, hPal)

End Function

'capturescreen函数捕捉整个屏幕图象

Public Function CaptureScreen() As Picture

Dim hWndScreen As Long

'获得桌面的窗口句柄

hWndScreen = GetDesktopWindow()

Set CaptureScreen = CaptureWindow(hWndScreen, False, 0, 0,

_

erPixelX, erPixelY)

End Function

Public Function CaptureActiveWindow() As Picture

Dim hWndActive As Long

Dim r As Long

Dim RectActive As RECT

hWndActive = GetForegroundWindow()

r = GetWindowRect(hWndActive, RectActive)

Set CaptureActiveWindow = CaptureWindow(hWndActive, False, 0, 0, _

- , -

)

End Function

Public Sub PrintPictureToFitPage(Prn As Printer, Pic As Picture)

Const vbHiMetric As Integer = 8

Dim PicRatio As Double

Dim PrnWidth As Double

Dim PrnHeight As Double

Dim PrnRatio As Double

Dim PrnPicWidth As Double

Dim PrnPicHeight As Double

If >= Then

ation = vbPRORPortrait

Else

ation = vbPRORLandscape

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End If

PicRatio = /

PrnWidth = (idth, ode, vbHiMetric)

PrnHeight = (eight, ode, vbHiMetric)

PrnRatio = PrnWidth / PrnHeight

If PicRatio >= PrnRatio Then

PrnPicWidth = (PrnWidth, vbHiMetric, ode)

PrnPicHeight = (PrnWidth / PicRatio, vbHiMetric,

ode)

Else

PrnPicHeight = (PrnHeight, vbHiMetric, ode)

PrnPicWidth = (PrnHeight * PicRatio, vbHiMetric,

ode)

End If

icture Pic, 0, 0, PrnPicWidth, PrnPicHeight

End Sub

Private Sub Command4_Click()

tExt = ".BMP"

= "Bitmap Image (*.bmp)|*.bmp"

ve

If me <> "" Then

SavePicture e, me

End If

End Sub

Private Sub Command5_Click()

PrintPictureToFitPage Printer, e

End Sub

Private Sub Form_Load()

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n = "捕捉整个屏幕"

n = "两秒钟后捕捉活动窗口"

n = "清除图象"

n = "保存图象"

n = "打印图象"

End Sub

运行程序，点击command1或者Command2就可以捕捉成个屏幕或者窗口到Picture1中，然后点击Command4或者Command5就可以保存或打印图象。

上面的程序中最重要的是CaptureWindow函数以及CreateBitmapPicture函数，CaptureWindow函数建立与要捕捉的窗口的绘图设备（Device Context）句柄相兼容的绘图设备（Device Context）句柄，然后建立相应的调色板，最后将绘图设备（Device Context）中的图象拷贝到一个hBitmap对象句柄中。CreateBitmapPicture函数则根据传递过来的hBitmap对象句柄和调色板句柄建立一个Picture对象。在将这个对象赋予PictureBox的Picture属性，然后就可以使用SavePicture函数来保存图象了。

OleCreatePictureIndirect函数支持的不仅有BMP图象，同时也支持Ico图标，所以利用该函数和ExtractIcon函数也可以提取并保存Windows文件中的图标。

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