请问如何快速读取贴图

mywatermelon

做一个游戏的时候需要快速地读取贴图，但是一张张贴图地读取的话需要大量的时间，曾经听人说过把所有的贴图组合成一张图片，那么读取的时候就只需要读取一张图片就可以了，读取以后再使用vb.net里面的Graphics.CopyFromScreen() 函数将大图片里面一张张贴图分解出来就可以了。但是想问问Graphics.CopyFromScreen()这个函数是怎样使用的呢？

Miu.C

CopyFromScreen没用过，不过一般绘图的函数都有参数的。
比如BitBlt就有。

mywatermelon

那么请问BitBlt函数是怎样使用的呢？

Miu.C

Bitblt作用将某一内存块的数据传送到另一内存块，前一内存块被称为"源"，后一内存块被称为"目标"图象程序开发者使用Blit的函数在内存中将某页面上的一幅位图经过一定的变换转移到另一个页面上
原形说明:
Declare Function BitBlt Lib "gdi32" Alias "BitBlt"(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
hDestDC As Long， //目标设备环境的句柄
x As Long， //目标设备环境的矩形区域的左上角的x坐标
y As Long， //目标设备环境的矩形区域的左上角的y坐标
nWidth As Long， //目标设备环境的矩形区域的宽度值
nHeight As Long， //目标设备环境的矩形区域的高度值
hSrcDC As Long， //源设备环境的句柄
xSrc As Long， //源设备环境的矩形区域的左上角的x坐标
ySrc As Long， //源设备环境的矩形区域的左上角的y坐标
dwRop As Long， //光栅操作符
dwRop参数是光栅操作代码(Rop)，它是指源位图与目标位图以及图案刷的颜色值进行布尔运算的方式，以下列出了常用的光栅操作码及含义
BLACKNESS 用黑色填充目标矩形区域.
DSTINVERT 将目标矩形图象进行反相.
MERGECOPY 将源矩形图象与指定的图案刷(Pattern)进行布尔"与"运算.
MERGEPAINT 将源矩形图形经过反相后，与目标矩形图象进行布尔"或"运算.
NOTSRCCOPY 将源矩形图象经过反相后，复制到目标矩形上.
NOTSRCERASE 先将源矩形图象与目标矩形图象进行布尔"或"运算，然后再将得图象进行反相.
PATCOPY 将指定的图案刷复制到目标矩形上.
PATINVERT 将指定的图案刷与目标矩形图象进行布尔"异或"运算.
PATPAINT 先将源矩形图象进行反相，与指定的图案刷进行布尔"或"运算，再与目标矩形图象进行布尔"或"运算SRCAND 将源矩形图象与目标矩形图象进行布尔"与"运算.
SRCCOPY 将源矩形图象直接复制到目标矩形上.
SRCERASE 将目标矩形图象进行反相，再与源矩形图象进行布尔"与"运算.
SRCINVERT 将源矩形图象与目标矩形图象进行布尔"异或"运算.
SRCPAINT 将源矩形图象与目标矩形图象进行布尔"或"运算.
WHITENESS 用白色填充目标矩形区域.

Miu.C

就我使用这个函数发现还有一点要注意，就是图形的单位要搞清楚，好像Visual Basic(.Net不知道)默认的单位是Twip，而Bitblt用的好象是Pixel，所以要转换单位才行。

xgreenclover

Twip是什么？

Miu.C

缇是用来展示空间或定义在纸张，或其他要打印的或在计算机显示器上显示区域上物体的量度。1缇等于1/1440英寸或1/567厘米。也就是说1英寸中有1440缇或1厘米中有567缇。1缇等于传统打印量度点的十二分之一。1点近似等于1/72英寸。

　　许多计算机程序，如微软的Visual Basic及其Rich-Text格式，需要程序员确定屏幕位置和图像，图标的大小，以缇为度量而不是像素。和像素相同，缇可以在屏幕分辨率改变时调整大小，但是不同于像素的是它表示了打印的绝对值。

　　由于不是所有的软件开发工具都使用缇，程序员有时需要在缇和像素之间进行转换。

mywatermelon

能否给小弟一个例子吗……小弟还是看不明白……假设picture1控件里面有张全身像，小弟想截取全身像的头部并复制到picture2控件中，这样应该怎么做呢？

Miu.C

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()
    '-> 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

Canbitwell

谢了
通过GetDIBits可以将hDC里的内容获得下来