Bitmaps

BitBlt

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 DC
 int nXDest, // x-coord of destination upper-left corner
 int nYDest, // y-coord of destination upper-left corner
 int nWidth, // width of destination rectangle
 int nHeight, // height of destination rectangle
 HDC hdcSrc, // handle to source DC
 int nXSrc, // x-coordinate of source upper-left corner
 int nYSrc, // y-coordinate of source upper-left corner
 DWORD dwRop // raster operation code
);

Parameters

hdcDest

[in] Handle to the destination device context.

nXDest

[in] Specifies the x-coordinate, in logical units, of the upper-left corner of the destination rectangle.

nYDest

[in] Specifies the y-coordinate, in logical units, of the upper-left corner of the destination rectangle.

nWidth

[in] Specifies the width, in logical units, of the source and destination rectangles.

nHeight

[in] Specifies the height, in logical units, of the source and the destination rectangles.

hdcSrc

[in] Handle to the source device context.

nXSrc

[in] Specifies the x-coordinate, in logical units, of the upper-left corner of the source rectangle.

nYSrc

[in] Specifies the y-coordinate, in logical units, of the upper-left corner of the source rectangle.

dwRop

[in] 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.)
CAPTUREBLT	Windows 98/Me, Windows 2000/XP: Includes any windows that are layered on top of your window in the resulting image. By default, the image only contains your window. Note that this generally cannot be used for printing device contexts.
DSTINVERT	Inverts the destination rectangle.
MERGECOPY	Merges the colors of the source rectangle with the brush currently selected in hdcDest, 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.
NOMIRRORBITMAP	Windows 98/Me, Windows 2000/XP: Prevents the bitmap from being mirrored.
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 brush currently selected in hdcDest, into the destination bitmap.
PATINVERT	Combines the colors of the brush currently selected in hdcDest, with the colors of the destination rectangle by using the Boolean XOR operator.
PATPAINT	Combines the colors of the brush currently selected in hdcDest, 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.

Windows NT/2000/XP: To get extended error information, call GetLastError.

Remarks

BitBlt only does clipping on the destination DC.

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 the GetDeviceCaps function as well as the following functions: MaskBlt, PlgBlt, and StretchBlt.

BitBlt returns an error if the source and destination device contexts represent different devices. To transfer data between DCs for different devices, convert the memory bitmap to a DIB by calling GetDIBits. To display the DIB to the second device, call SetDIBits or StretchDIBits.

ICM: No color management is performed when blits occur.

Requirements

  Windows NT/2000/XP: Included in Windows NT 3.1 and later.
  Windows 95/98/Me: Included in Windows 95 and later.
  Header: Declared in Wingdi.h; include Windows.h.
  Library: Use Gdi32.lib.

Example Code

Capturing an Image

You can use a bitmap to capture an image, and you can store the captured image in memory, display it at a different location in your application's window, or display it in another window.

In some cases, you may want your application to capture images and store them only temporarily. For example, when you scale or zoom a picture created in a drawing application, the application must temporarily save the normal view of the image and display the zoomed view. Later, when the user selects the normal view, the application must replace the zoomed image with a copy of the normal view that it temporarily saved.

To store an image temporarily, your application must call CreateCompatibleDC to create a DC that is compatible with the current window DC. After you create a compatible DC, you create a bitmap with the appropriate dimensions by calling the CreateCompatibleBitmap function and then select it into this device context by calling the SelectObject function.

After the compatible device context is created and the appropriate bitmap has been selected into it, you can capture the image. The BitBlt function captures images. This function performs a bit block transfer that is, it copies data from a source bitmap into a destination bitmap. However, the two arguments to this function are not bitmap handles. Instead, BitBlt receives handles that identify two device contexts and copies the bitmap data from a bitmap selected into the source DC into a bitmap selected into the target DC. In this case, the target DC is the compatible DC, so when BitBlt completes the transfer, the image has been stored in memory. To redisplay the image, call BitBlt a second time, specifying the compatible DC as the source DC and a window (or printer) DC as the target DC.

The following example code, from an application that captures an image of the entire desktop, creates a compatible device context and a bitmap with the appropriate dimensions, selects the bitmap into the compatible DC, and then copies the image using the BitBlt function.

// Create a normal DC and a memory DC for the entire screen. The 
// normal DC provides a "snapshot" of the screen contents. The 
// memory DC keeps a copy of this "snapshot" in the associated 
// bitmap. 
 
hdcScreen = CreateDC("DISPLAY", NULL, NULL, NULL); 
hdcCompatible = CreateCompatibleDC(hdcScreen); 
 
// Create a compatible bitmap for hdcScreen. 
 
hbmScreen = CreateCompatibleBitmap(hdcScreen, 
 GetDeviceCaps(hdcScreen, HORZRES), 
 GetDeviceCaps(hdcScreen, VERTRES)); 
 
if (hbmScreen == 0) 
 errhandler("hbmScreen", hwnd); 
 
// Select the bitmaps into the compatible DC. 
 
if (!SelectObject(hdcCompatible, hbmScreen)) 
 errhandler("Compatible Bitmap Selection", hwnd); 
 
 // Hide the application window. 
 
 ShowWindow(hwnd, SW_HIDE); 
 
 //Copy color data for the entire display into a 
 //bitmap that is selected into a compatible DC. 
 
 if (!BitBlt(hdcCompatible, 
 0,0, 
 bmp.bmWidth, bmp.bmHeight, 
 hdcScreen, 
 0,0, 
  SRCCOPY)) 
 
 errhandler("Screen to Compat Blt Failed", hwnd); 
 
 // Redraw the application window. 
 
 ShowWindow(hwnd, SW_SHOW);