[GRASS-dev] question about the concept 'window'

[Peng Du]

Hi

In function static int compute_window_row(int fd, int row, int *cellRow) 
in ~/grass/7.0/grass_trunk/lib/raster/get_row.c, there is a check to see 
if row is in window, and if not, 0 is returned.

I came across this function from get_map_row_nomask(...) in the same 
file (which came all the way from Rast_get_row(fds[i], rowbuf, row, 
maptype);), and the result of compute_window_row(...) is used to 
determined whether to "read cell file row if not in memory".

I'm a little confused about the concept 'window' here, and how does that 
relate to "in memory"?

My understanding is that "window" is a "visible area", and rows are only 
read from disk file if it's within this "window" area. Then what would 
happen if rast_get_row is used to get the exact same row in exact the 
same map more than once? Does the second time NOT read the row from file 
because the first time has put this row in memory? In this case the 
requested row is copied from a inner buffer that was filled with the 
data during the first time call?

Thanks,
Peng