InvertRgn

InvertRgn
Header:	Quickdraw.h		Carbon status:	Supported

Inverts the pixels enclosed by a region.

void InvertRgn (
     rgn
);

Parameter descriptions

rgn: A handle to the region whose pixels are to invert.

DISCUSSION

The InvertRgn function inverts the pixels enclosed by the region whose handle you pass in the rgn parameter. Every white pixel becomes black and every black pixel becomes white.

This function leaves the location of the graphics pen unchanged.

This function depends on the local coordinate system of the current graphics port. If you draw a region in a graphics port different from the one in which you defined the region, it may not appear in the proper position in the graphics port.

If any horizontal or vertical line drawn through the region would intersect the region’s outline more than 50 times, the results of this graphics operation are undefined.

SPECIAL CONSIDERATIONS

The InvertRgn function was designed for 1-bit images in basic graphics ports. This function operates on color pixels in color graphics ports, but the results are predictable only with 1-bit or direct pixels. For indexed pixels, Color QuickDraw performs the inversion on the pixel indexes, which means the results depend entirely on the contents of the CLUT. The eight colors used in basic QuickDraw are stored in a color table represented by the global variable QDColors. To display those eight basic QuickDraw colors on an indexed device, Color QuickDraw uses the Color Manager to obtain indexes to the colors in the CLUT that best map to the colors in the QDColors color table. Because the index, not the color value, is inverted, the results are unpredictable.

Inversion works better for direct pixels. Inverting a pure green, for example, that has red, green, and blue component values of $0000, $FFFF, and $0000 results in magenta, which has component values of $FFFF, $0000, and $FFFF.

The InvertRgn function may move or purge memory blocks in the application heap; do not call this function at interrupt time.

AVAILABILITY

Supported in Carbon. Available in Carbon 1.0.2 and later when running Mac OS 8.1 or later.