[GRASS-dev] GRASS 6.3.0 to be released

[Glynn Clements]

Hamish wrote:

> > After 6 release candidates, even tested on MS-Windows,
> > I don't see any real blockers any more. I suggest to get out
> > 6.3.0 this week and proceed with change to 6.4.release_branch/7.0.svn.
> > 
> > We can have 6.3.1 if needed.
> > 
> > Sounds ok?
> 
> to me, trac bug #72 is a blocker (PNG driver rendering offset)
>   http://trac.osgeo.org/grass/ticket/72

That issue has always been there, and isn't easily fixed.

Lines are drawn along the "nearest" axis. E.g. for a line which is
closer to the horizontal than to the vertical, the loop iterates over
the X coordinates, with the Y coordinate determined using Bressenham's
algorithm. The slope is always less than or equal to one, so at each
step the Y coordinate either remains unchanged or increments by one,
according to a test which only uses integer arithmetic.

Polygons are drawn from top to bottom as a single entity (as opposed
to the outline, which is a sequence of individual line segments). For
each row, the X coordinates of the left and right edges are calculated
using floating-point coordinates, then rounded to the nearest integer. 
A horizontal line (actually, a one-pixel-high rectangle) is drawn
between the two edge points.

It wouldn't be particularly hard to make the closer-to-vertical case
match, by using the same algorithm in both cases. Making the
closer-to-horizontal case match is harder (and messy).

But ultimately, this is just one aspect of a more fundamental problem:
integer coordinates and odd line widths simply don't mix. You cannot
get this case "right"; you just have to choose which flavour of
"wrong" you prefer.

[X11 largely ducked the issue by stating that single-pixel lines are
implementation dependent. Apart from shielding the X developers from
flak from users who would have preferred a different flavour of
"wrong" (even to the point of insisting that a particular flavour is
actually "the right one"), it allows the use of any line-drawing
functionality which is provided by the video hardware, regardless of
which flavour the hardware uses.]

-- 
Glynn Clements <glynn at gclements.plus.com>