On Fri, Oct 15, 2010 at 5:15 PM, Stefan Salewski <m...@ssalewski.de> wrote: > On Fri, 2010-10-15 at 11:54 -0700, Andrew Poelstra wrote: > >> >> The reason for it is that this is generally how drawing canvases work, >> so from a programmer's perspective, it is simpler to have y pointing down. >> > > WHY? >
Mainly because that has been the standard at least since Televisions were invented. The beam in a CRT scans from left-to-right, top-to-bottom. It's codified in the NTSC standard. So (x,y)=(0,0) is the upper left corner. Why are CRT's like this? Probably because words in books are also oriented left-to-right, top-to-bottom. Maybe if the television had been invented in the middle-east it would be different. I've got several digital image processing books on my shelf, the oldest is from 1972. Every one of them defines (x,y)=(0,0) as the upper left corner of an image. y as positive down, and x as positive right is simply the de-facto standard in digital image processing. _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user