Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 2 - Basic QuickDraw / Basic QuickDraw Reference

Routines / Manipulating Points in Graphics Ports

GetPixel

To determine whether the pixel associated with a point is black or white, use the GetPixel function.

FUNCTION GetPixel (h,v:\xDDInteger):\xDDBoolean;

h

The horizontal coordinate of the point for the pixel to be tested.

v

The vertical coordinate of the point for the pixel to be tested.

DESCRIPTION

The GetPixel function examines the pixel at the point specified by the h and v parameters and returns TRUE if the pixel is black or FALSE if it is white.

The selected pixel is immediately below and to the right of the point whose coordinates you supply in the h and v parameters, in the local coordinates of the current graphics port. There's no guarantee that the specified pixel actually belongs to the current graphics port, however; it may have been drawn in a graphics port overlapping the current one. To see if the point indeed belongs to the current graphics port, you could use the PtInRgn function (described in the chapter "QuickDraw Drawing" in this book) to test whether the point is in the current graphics port's visible region, as shown here.

PtInRgn(pt, thePort^.visRgn);