Standard getscanline routine prototype.
Source position: graphh.inc line 567
type getscanlineproc = procedure(  | 
X1: SmallInt;  | 
X2: SmallInt;  | 
Y: SmallInt;  | 
var data  | 
);  | 
This routine is used for FloodFill It returns an entire screen scan line with a word for each pixel in the scanline. Also handy for GetImage.