CDC::SelectClipRgn

virtual int SelectClipRgn( CRgn* pRgn );

int SelectClipRgn( CRgn* pRgn, int nMode );

Return Value

The region’s type. It can be any of the following values:

COMPLEXREGION New clipping region has overlapping borders.
ERROR Device context or region is not valid.
NULLREGION New clipping region is empty.
SIMPLEREGION New clipping region has no overlapping borders.

Parameters

pRgn

Identifies the region to be selected.

For the first version of this function, if this value is NULL, the entire client area is selected and output is still clipped to the window.
For the second version of this function, this handle can be NULL only when the RGN_COPY mode is specified.

nMode

Specifies the operation to be performed. It must be one of the following values:

RGN_AND The new clipping region combines the overlapping areas of the current clipping region and the region identified by pRgn.
RGN_COPY The new clipping region is a copy of the region identified by pRgn. This is functionality is identical to the first version of SelectClipRgn. If the region identified by pRgn is NULL, the new clipping region becomes the default clipping region (a null region).
RGN_DIFF The new clipping region combines the areas of the current clipping region with those areas excluded from the region identified by pRgn.
RGN_OR The new clipping region combines the current clipping region and the region identified by pRgn.
RGN_XOR The new clipping region combines the current clipping region and the region identified by pRgn but excludes any overlapping areas.

Remarks

Selects the given region as the current clipping region for the device context. Only a copy of the selected region is used. The region itself can be selected for any number of other device contexts, or it can be deleted.

The function assumes that the coordinates for the given region are specified in device units. Some printer devices support text output at a higher resolution than graphics output in order to retain the precision needed to express text metrics. These devices report device units at the higher resolution, that is, in text units. These devices then scale coordinates for graphics so that several reported device units map to only 1 graphic unit. You should always call the SelectClipRgn function using text units.

Applications that must take the scaling of graphics objects in the GDI can use the GETSCALINGFACTOR printer escape to determine the scaling factor. This scaling factor affects clipping. If a region is used to clip graphics, GDI divides the coordinates by the scaling factor. If the region is used to clip text, GDI makes no scaling adjustment. A scaling factor of 1 causes the coordinates to be divided by 2; a scaling factor of 2 causes the coordinates to be divided by 4; and so on.

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