Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 3 - QuickDraw Drawing / QuickDraw Drawing Reference

Routines / Drawing Polygons

InvertPoly

To invert the pixels enclosed by a polygon, use the InvertPoly procedure.

PROCEDURE InvertPoly (poly:\xDDPolyHandle);

poly

A handle to a polygon, the pixels of which you want to invert.

DESCRIPTION

The InvertPoly procedure 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 procedure leaves the location of the graphics pen unchanged.

SPECIAL CONSIDERATIONS

The InvertPoly procedure was designed for 1-bit images in basic graphics ports. This procedure 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 (which is described in the chapter "Color QuickDraw"). 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 procedure may move or purge memory blocks in the application heap. Your application should not call this procedure at interrupt time.