AlphaBlend

[This is preliminary documentation and subject to change.]

The AlphaBlend function displays bitmaps that have transparent or semitransparent pixels.

AlphaBlend(
  HDC hdcDest,
  int nXOriginDest,
  int nYOriginDest,
  int nWidthDest,
  int hHeightDest,
  HDC hdcSrc,
  int nXOriginSrc,
  int nYOriginSrc,
  int nWidthSrc,
  int nHeightSrc,
  BLENDFUNCTION blendFunction
);
 

Parameter

hdcDest

Handle to the destination device context.

nXOriginDest

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

nYOriginDest

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

nWidthDest

Specifies the width, in logical units, of the destination rectangle.

hHeightDset

Handle to the height, in logical units, of the destination rectangle.

hdcSrc

Handle to the source device context.

nXOriginSrc

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

nYOriginSrc

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

nWidthSrc

Specifies the width, in logical units, of the source rectangle.

nHeightSrc

Specifies the height, in logical units, of the source rectangle.

blendFunction

Specifies the alpha blending function for source and destination bitmaps, a global alpha value to be applied to the entire source bitmap, and format information for the source bitmap. The source and destination blend functions are currently limited to AC_SRC_OVER. See the BLENDFUNCTION and EMRALPHABLEND structures.

Return Values

If the function succeeds, the return value is TRUE.

If the function fails, the return value is FALSE.

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

Remarks

If the source rectangle and destination rectangle are not the same size, the source bitmap is stretched to match the destination rectangle. If the SetStretchBltMode function is used, the iStretchMode value is BLACKONWHITE and WHITEONBLACK; the iStretchMode value is automatically converted to COLORONCOLOR for this function.

The destination coordinates are transformed by using the transformation currently specified for the destination device context. The source coordinates are transformed by using the transformation currently specified for the source device context.

An error occurs (and the function returns FALSE) if the source device context identifies an enhanced metafile device context.

If destination and source bitmaps do not have the same color format, AlphaBlend converts the source bitmap to match the destination bitmap.

AlphaBlend does not support mirroring. If either the width or height of the source or destination is negative, this call will fail.

Note: The SourceConstantaAlpha member of BLENDFUNCTION specifies an alpha transparancy value to be used on the entire source bitmap. The SourceConstantAlpha value is combined with any per-pixel alpha values. If you set SourceConstantAlpha to 0, it is assumed that your image is transparent. Set the SourceConstantAlpha value to 255 (indicates that the image is opaque) when you only want to use per-pixel alpha values.

QuickInfo

  Windows NT: Requires version 5.0 or later.
  Windows: Requires Windows 98 or later.
  Windows CE: Unsupported.
  Header: Declared in wingdi.h.
  Import Library: Included as a resource in msimg32.dll.

See Also

Bitmaps Overview, Bitmap Functions