Lee's C++ Builder Programming Notes: Bitmap: 位元塊傳輸 BitBlt

當我們想將圖像從視訊顯示的某個區域複製到另外一個區域時, 可以考慮使用 Windows 圖形裝置介面 (Graphics Device Interface, GDI) 所提供的位元塊傳輸 ( bit-block transfer ) 函式 BitBlt。BitBlt 讀作 bit blit, 有關 Bit Blit 這個指令的來源, 在維基百科有相當詳細的描述; 除此, 維基百科還用小精靈為例子, 介紹關於背景圖片與 BitBlt 的使用方法, 值得一看...

The BitBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context.

BOOL BitBlt(
　HDC hdcDest,
　　// handle to destination device context
　int nXDest,
　　// x-coordinate of destination rectangle's upper-left corner
　int nYDest,
　　// y-coordinate of destination rectangle's upper-left corner
　int nWidth,
　　// width of destination rectangle
　int nHeight,
　　// height of destination rectangle
　HDC hdcSrc,
　　// handle to source device context
　int nXSrc,
　　// x-coordinate of source rectangle's upper-left corner
　int nYSrc,
　　// y-coordinate of source rectangle's upper-left corner
　DWORD dwRop
　　// raster operation code
);

Parameters
hdcDest　Identifies the destination device context.

nXDest　Specifies the logical x-coordinate of the upper-left corner of the destination rectangle.

nYDest　Specifies the logical y-coordinate of the upper-left corner of the destination rectangle.

nWidth　Specifies the logical width of the source and destination rectangles.

nHeight　Specifies the logical height of the source and the destination rectangles.

hdcSrc　Identifies the source device context.

nXSrc　Specifies the logical x-coordinate of the upper-left corner of the source rectangle.

nYSrc　Specifies the logical y-coordinate of the upper-left corner of the source rectangle.

dwRop　Specifies a raster-operation code. These codes define how the color data for the source rectangle is to be combined with the color data for the destination rectangle to achieve the final color.

The following list shows some common raster operation codes:

Value Description
BLACKNESS 　Fills the destination rectangle using the color associated with index 0 in the physical palette. (This color is black for the default physical palette.)

DSTINVERT 　Inverts the destination rectangle.

MERGECOPY　Merges the colors of the source rectangle with the specified pattern by using the Boolean AND operator.

MERGEPAINT 　Merges the colors of the inverted source rectangle with the colors of the destination rectangle by using the Boolean OR operator.

NOTSRCCOPY　Copies the inverted source rectangle to the destination.

NOTSRCERASE　Combines the colors of the source and destination rectangles by using the Boolean OR operator and then inverts the resultant color.

PATCOPY 　Copies the specified pattern into the destination bitmap.

PATINVERT 　Combines the colors of the specified pattern with the colors of the destination rectangle by using the Boolean XOR operator.

PATPAINT　Combines the colors of the pattern with the colors of the inverted source rectangle by using the Boolean OR operator. The result of this operation is combined with the colors of the destination rectangle by using the Boolean OR operator.

SRCAND 　Combines the colors of the source and destination rectangles by using the Boolean AND operator.

SRCCOPY 　Copies the source rectangle directly to the destination rectangle.

SRCERASE 　Combines the inverted colors of the destination rectangle with the colors of the source rectangle by using the Boolean AND operator.

SRCINVERT 　Combines the colors of the source and destination rectangles by using the Boolean XOR operator.

SRCPAINT 　Combines the colors of the source and destination rectangles by using the Boolean OR operator.

WHITENESS　Fills the destination rectangle using the color associated with index 1 in the physical palette. (This color is white for the default physical palette.)

Return Values
If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks
If a rotation or shear transformation is in effect in the source device context, BitBlt returns an error. If other transformations exist in the source device context (and a matching transformation is not in effect in the destination device context), the rectangle in the destination device context is stretched, compressed, or rotated as necessary.

If the color formats of the source and destination device contexts do not match, the BitBlt function converts the source color format to match the destination format.

When an enhanced metafile is being recorded, an error occurs if the source device context identifies an enhanced-metafile device context.

Not all devices support the BitBlt function. For more information, see the RC_BITBLT raster capability entry in GetDeviceCaps.

BitBlt returns an error if the source and destination device contexts represent different devices.