Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!bloom-beacon!AMD-26.HAC.COM!dhuff
From: dhuff@AMD-26.HAC.COM (Daryl Huff)
Newsgroups: comp.windows.x
Subject: X Windows Fill Rule
Message-ID: <8906022017.AA21838@amd-26.hac.com>
Date: 2 Jun 89 20:17:55 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 30

The frame buffer includes hardware rendering of some of the X defined
graphics primitives such as fonts, lines, and polygon fills.

     The fill rule specified by X Windows differs from the fill algorithm
used by our hardware.  Our hardware fills the border of the polygon 
according to an ideal Bresenham's line drawn between two consecutive
vertices of a polygon while the X Windows fill rule does not.  The X 
Windows rule appears to truncate the fractional
portion of the pixel value.  For example a fill rectangle, as defined by
the X Windows fill rule, will not fill the right column of pixels or the 
bottom row of pixels but our hardware rendering device will.

     My questions are:

     1)  Why does X Windows use this fill rule?  When you specify a 
         rectangle to be filled isn't it reasonable to expect that the
         entire rectangle will be filled?

     2)  Is it critical that I somehow force our hardware to use a more
         primitive fill algorithm?  Does anyone see a problem with just
         using the fill algorithm we have implemented in hardware?

     3)  Why does X specify a fill rule anyway?  There are different 
         circle and line algorithms yet X does not specify which one of
         these to use.
 
     Any opinions you may have are welcome.

                                    Daryl Huff
                                    Hughes Aircraft Company (GSG)