GdiAlphaBlend function (wingdi.h)
The GdiAlphaBlend function displays bitmaps that have transparent or semitransparent pixels.
Syntax
BOOL GdiAlphaBlend(
[in] HDC hdcDest,
[in] int xoriginDest,
[in] int yoriginDest,
[in] int wDest,
[in] int hDest,
[in] HDC hdcSrc,
[in] int xoriginSrc,
[in] int yoriginSrc,
[in] int wSrc,
[in] int hSrc,
[in] BLENDFUNCTION ftn
);
Parameters
[in] hdcDest
A handle to the destination device context.
[in] xoriginDest
The x-coordinate, in logical units, of the upper-left corner of the destination rectangle.
[in] yoriginDest
The y-coordinate, in logical units, of the upper-left corner of the destination rectangle.
[in] wDest
The width, in logical units, of the destination rectangle.
[in] hDest
The height, in logical units, of the destination rectangle.
[in] hdcSrc
A handle to the source device context.
[in] xoriginSrc
The x-coordinate, in logical units, of the upper-left corner of the source rectangle.
[in] yoriginSrc
The y-coordinate, in logical units, of the upper-left corner of the source rectangle.
[in] wSrc
The width, in logical units, of the source rectangle.
[in] hSrc
The height, in logical units, of the source rectangle.
[in] ftn
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 value
If the function succeeds, the return value is TRUE.
If the function fails, the return value is FALSE.
This function can return the following value.
| Return code | Description |
|---|---|
|
One or more of the input parameters is invalid. |
Remarks
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, GdiAlphaBlend converts the source bitmap to match the destination bitmap.
GdiAlphaBlend does not support mirroring. If either the width or height of the source or destination is negative, this call will fail.
When rendering to a printer, first call GetDeviceCaps with SHADEBLENDCAPS to determine if the printer supports blending with GdiAlphaBlend. Note that, for a display DC, all blending operations are supported and these flags represent whether the operations are accelerated.
If the source and destination are the same surface, that is, they are both the screen or the same memory bitmap and the source and destination rectangles overlap, an error occurs and the function returns FALSE.
The source rectangle must lie completely within the source surface, otherwise an error occurs and the function returns FALSE.
GdiAlphaBlend fails if the width or height of the source or destination is negative.
The SourceConstantAlpha member of BLENDFUNCTION specifies an alpha transparency value to be used on the entire source bitmap. The SourceConstantAlpha value is combined with any per-pixel alpha values. If SourceConstantAlpha is 0, it is assumed that the image is transparent. Set the SourceConstantAlpha value to 255 (which indicates that the image is opaque) when you only want to use per-pixel alpha values.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 2000 Professional [desktop apps only] |
| Minimum supported server | Windows 2000 Server [desktop apps only] |
| Target Platform | Windows |
| Header | wingdi.h (include Windows.h) |
| Library | Gdi32.lib |
| DLL | Gdi32.dll |