mojave man page for getpixel

getpixel(3alleg4)						  Allegro manual						 getpixel(3alleg4)

NAME
       getpixel - Reads a pixel from a bitmap. Allegro game programming library.

SYNOPSIS
       #include <allegro.h>

       int getpixel(BITMAP *bmp, int x, int y);

DESCRIPTION
       Reads a pixel from point (x, y) in the bitmap.

RETURN VALUE
       Returns	-1 if the point lies outside the bitmap (ignoring the clipping rectangle), otherwise the value of the pixel in the color format of
       the bitmap.

       Warning: -1 is also a valid value for pixels contained in 32-bit bitmaps with alpha channel (when R,G,B,A are all  equal  to  255)  so  you
       can't use the test against -1 as a predicate for such bitmaps. In this cases, the only reliable predicate is is_inside_bitmap().

       To extract the individual color components, use the getr() / getg() / getb() / geta() family of functions.

SEE ALSO
       putpixel(3alleg4),    _getpixel(3alleg4),    is_inside_bitmap(3alleg4),	 getr(3alleg4),   getg(3alleg4),   getb(3alleg4),   geta(3alleg4),
       ex12bit(3alleg4), exalpha(3alleg4), exflame(3alleg4), exlights(3alleg4)

Allegro 							   version 4.4.2						 getpixel(3alleg4)