InvertPoly

InvertPoly
Header:	Quickdraw.h		Carbon status:	Supported

Inverts the pixels enclosed by a polygon.

void InvertPoly (
    PolyHandle poly
);

Parameter descriptions

poly: A handle to a polygon, the pixels of which you want to invert. The OpenPoly function returns this handle when you first create the polygon.

DISCUSSION

The InvertPoly function inverts the pixels enclosed by the polygon whose handle you pass in the poly parameter. Every white pixel becomes black and every black pixel becomes white.

This function leaves the location of the graphics pen unchanged.

InvertPoly temporarily converts the polygon into a region to perform their operations. The amount of memory required for this temporary region may be far greater than the amount required by the polygon alone.

You can estimate the size of this region by scaling down the polygon with the MapPoly, converting the polygon into a region, checking the region’s size with the Memory Manager function GetHandleSize, and multiplying that value by the factor by which you scaled the polygon.

The result of this graphics operation is undefined whenever any horizontal or vertical line drawn through the polygon would intersect the polygon’s outline more than 50 times.

SPECIAL CONSIDERATIONS

The InvertPoly 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 InvertPoly 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.