InvertArc

InvertArc
Header:	Quickdraw.h		Carbon status:	Supported

Inverts the pixels of a wedge.

void InvertArc (
    const Rect *r, 
    SInt16 startAngle, 
    SInt16 arcAngle
);

Parameter descriptions

r: The rectangle that defines an oval’s boundaries.
startAngle: The angle indicating the start of the arc.
arcAngle: The angle indicating the arc’s extent.

DISCUSSION

The InvertArc function inverts the pixels enclosed by a wedge of the oval bounded by the rectangle that you specify in the r parameter. Every white pixel becomes black and every black pixel becomes white. As in FrameArc, use the startAngle and arcAngle parameters to define the arc of the wedge.

This function leaves the location of the graphics pen unchanged.

SPECIAL CONSIDERATIONS

The InvertArc 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 direct devices or 1-bit pixel maps. 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 InvertArc 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.