GetDIBits 的参数问题

[橘子皮...]

VB声明
Declare Function GetDIBits Lib "gdi32" Alias "GetDIBits" (ByVal aHDC As Long, ByVal hBitmap As Long, ByVal nStartScan As Long, ByVal nNumScans As Long, lpBits As Any, lpBI As BITMAPINFO, ByVal wUsage As Long) As Long
说明
将来自一幅位图的二进制位复制到一幅与设备无关的位图里
返回值
Long，非零表示成功，零表示失败。在Windows 95中，返回值是返回的扫描线数量
参数表
参数 类型及说明
aHDC Long，定义了与设备有关位图hBitmap的配置信息的一个设备场景的句柄
hBitmap Long，源位图的句柄。绝对不能将这幅位图选入设备场景
nStartScan Long，欲复制到DIB中的第一条扫描线的编号
nNumScans Long，欲复制的扫描线数量
lpBits Any，指向一个缓冲区的指针。这个缓冲区将用于装载采用DIB格式的信息，但不取回数据（用ByVal传递零值）
lpBI BITMAPINFO，对lpBits DIB的格式及颜色进行说明的一个结构。在BITMAPINFOHEADER结构中，从biSize到biCompression之间的所有字段都必须初始化
wUsage Long，下述常数之一：
DIB_PAL_COLORS 在颜色表中装载一个16位所以数组，它们与当前选定的调色板有关
DIB_RGB_COLORS 在颜色表中装载RGB颜色
注解
起始扫描线与起点有关。除非将BITMAPINFOHEADER结构的biHeight字段设为负值，否则起点就位于左下角


上面是我的API文档里的说明，他第2个参数说"绝对不能将这幅位图选入设备场景",这句话怎么理解呢？？

如果我这样写
mHdc = CreateCompatibleDC(0)
mDib = CreateDIBSection(mHdc, bMapinfo, DIB_RGB_COLORS, mPtr, 0, 0)
mOldDib = SelectObject(mHdc, mDib)

GetDIBits mHdc, mDib, 0, lHeight, p(1, 1), bMapinfo, DIB_RGB_COLORS
这样可以吗？还是必须把mHdc换成GetDC(0)啥的？？？

[worldy]

mHdc = CreateCompatibleDC(0)
mDib = CreateDIBSection(mHdc, bMapinfo, DIB_RGB_COLORS, mPtr, 0, 0)
mOldDib = SelectObject(mHdc, mDib)

GetDIBits mHdc, mDib, 0, lHeight, p(1, 1), bMapinfo, DIB_RGB_COLORS

CreateDIBSection前，必须为bMapinfo设置成员值就可以，但你得到的将是没有是一个全黑的位图

如果才获得窗口位图，GetDIBits 前，必须使用Bitblt将窗口位图拷贝入mHdc

[worldy]

话说，既然使用CreateDIBSection，一般就不需要使用GetDIBits ，因为CreateDIBSection已经可以直接获得访问位图的指针

[贝隆]

'Example Name:DIB
Private Const BI_RGB = 0&
Private Const DIB_RGB_COLORS = 0 '  color table in RGBs
Private Type BITMAPINFOHEADER '40 bytes
        biSize As Long
        biWidth As Long
        biHeight As Long
        biPlanes As Integer
        biBitCount As Integer
        biCompression As Long
        biSizeImage As Long
        biXPelsPerMeter As Long
        biYPelsPerMeter As Long
        biClrUsed As Long
        biClrImportant As Long
End Type
Private Type RGBQUAD
        rgbBlue As Byte
        rgbGreen As Byte
        rgbRed As Byte
        rgbReserved As Byte
End Type
Private Type BITMAPINFO
        bmiHeader As BITMAPINFOHEADER
        bmiColors As RGBQUAD
End Type
Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function CreateDIBSection Lib "gdi32" (ByVal hdc As Long, pBitmapInfo As BITMAPINFO, ByVal un As Long, ByVal lplpVoid As Long, ByVal handle As Long, ByVal dw As Long) As Long
Private Declare Function GetDIBits Lib "gdi32" (ByVal aHDC As Long, ByVal hBitmap As Long, ByVal nStartScan As Long, ByVal nNumScans As Long, lpBits As Any, lpBI As BITMAPINFO, ByVal wUsage As Long) As Long
Private Declare Function SetDIBitsToDevice Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal dx As Long, ByVal dy As Long, ByVal SrcX As Long, ByVal SrcY As Long, ByVal Scan As Long, ByVal NumScans As Long, Bits As Any, BitsInfo As BITMAPINFO, ByVal wUsage As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long
Private Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long
Dim iBitmap As Long, iDC As Long
Private Sub Form_Paint()
    'KPD-Team 2000
    'URL: http://www.allapi.net/
    'E-Mail: [e-mail]
    '-> Compile this code for better performance
    Dim bi24BitInfo As BITMAPINFO, bBytes() As Byte, Cnt As Long
    With bi24BitInfo.bmiHeader
        .biBitCount = 24
        .biCompression = BI_RGB
        .biPlanes = 1
        .biSize = Len(bi24BitInfo.bmiHeader)
        .biWidth = 100
        .biHeight = 100
    End With
    ReDim bBytes(1 To bi24BitInfo.bmiHeader.biWidth * bi24BitInfo.bmiHeader.biHeight * 3) As Byte
    iDC = CreateCompatibleDC(0)
    iBitmap = CreateDIBSection(iDC, bi24BitInfo, DIB_RGB_COLORS, ByVal 0&, ByVal 0&, ByVal 0&)
    SelectObject iDC, iBitmap
    BitBlt iDC, 0, 0, bi24BitInfo.bmiHeader.biWidth, bi24BitInfo.bmiHeader.biHeight, GetDC(0), 0, 0, vbSrcCopy
    GetDIBits iDC, iBitmap, 0, bi24BitInfo.bmiHeader.biHeight, bBytes(1), bi24BitInfo, DIB_RGB_COLORS
    For Cnt = LBound(bBytes) To UBound(bBytes)
        If bBytes(Cnt) < 50 Then
            bBytes(Cnt) = 0
        Else
            bBytes(Cnt) = bBytes(Cnt) - 50
        End If
    Next Cnt
    SetDIBitsToDevice Me.hdc, 0, 0, bi24BitInfo.bmiHeader.biWidth, bi24BitInfo.bmiHeader.biHeight, 0, 0, 0, bi24BitInfo.bmiHeader.biHeight, bBytes(1), bi24BitInfo, DIB_RGB_COLORS
    DeleteDC iDC
    DeleteObject iBitmap
End Sub

[橘子皮...]

如果是
mHdc = CreateCompatibleDC(hdc)
hBmp = CreateCompatibleBitmap(hdc, lWidth, lHeight)
SelectObject mHdc, hBmp

GetDIBits mHdc, hBmp, 0, lHeight, p(1, 1), bMapinfo, DIB_RGB_COLORS
也可以吗？？？？ 位图已经选入了哦

[橘子皮...]

谁给写个代码例子，什么情况下不能第2个参数不能用