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.