CDC::SetStretchBltMode

int SetStretchBltMode( int nStretchMode );

Return Value

The previous stretching mode. It can be STRETCH_ANDSCANS, STRETCH_DELETESCANS, or STRETCH_ORSCANS.

Parameters

nStretchMode

Specifies the stretching mode. It can be any of the following values:

Value	Description
BLACKONWHITE	Performs a Boolean AND operation using the color values for the eliminated and existing pixels. If the bitmap is a monochrome bitmap, this mode preserves black pixels at the expense of white pixels.
COLORONCOLOR	Deletes the pixels. This mode deletes all eliminated lines of pixels without trying to preserve their information.
HALFTONE	Maps pixels from the source rectangle into blocks of pixels in the destination rectangle. The average color over the destination block of pixels approximates the color of the source pixels.
	After setting the HALFTONE stretching mode, an application must call the Win32 function ::SetBrushOrgEx to set the brush origin. If it fails to do so, brush misalignment occurs.
STRETCH_ANDSCANS	Windows 95: Same as BLACKONWHITE
STRETCH_DELETESCANS	Windows 95: Same as COLORONCOLOR
STRETCH_HALFTONE	Windows 95: Same as HALFTONE.
STRETCH_ORSCANS	Windows 95: Same as WHITEONBLACK
WHITEONBLACK	Performs a Boolean OR operation using the color values for the eliminated and existing pixels. If the bitmap is a monochrome bitmap, this mode preserves white pixels at the expense of black pixels.

Remarks

Sets the bitmap-stretching mode for the StretchBlt member function. The bitmap-stretching mode defines how information is removed from bitmaps that are compressed by using the function.

The BLACKONWHITE (STRETCH_ANDSCANS) and WHITEONBLACK (STRETCH_ORSCANS) modes are typically used to preserve foreground pixels in monochrome bitmaps. The COLORONCOLOR (STRETCH_DELETESCANS) mode is typically used to preserve color in color bitmaps.

The HALFTONE mode requires more processing of the source image than the other three modes; it is slower than the others, but produces higher quality images. Also note that SetBrushOrgEx must be called after setting the HALFTONE mode to avoid brush misalignment.

Additional stretching modes might also be available depending on the capabilities of the device driver.

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