SetStretchBltMode

The SetStretchBltMode function sets the bitmap stretching mode in the specified device context.

int SetStretchBltMode(

HDC hdc,	// handle of device context
int iStretchMode	// bitmap stretching mode
);

Parameters

hdc

Identifies the device context.

iStretchMode

Specifies the stretching mode. It can be one 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 SetBrushOrgEx function to set the brush origin. If it fails to do so, brush misalignment occurs.
STRETCH_ANDSCANS	Same as BLACKONWHITE.
STRETCH_DELETESCANS	Same as COLORONCOLOR.
STRETCH_HALFTONE	Same as HALFTONE.
STRETCH_ORSCANS	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.

Return Values

If the function succeeds, the return value is the previous stretching mode.

If the function fails, the return value is zero.

Remarks

The stretching mode defines how Windows combines rows or columns of a bitmap with existing pixels on a display device when an application calls the StretchBlt 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.

See Also

GetStretchBltMode, SetBrushOrgEx, StretchBlt

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