Re: smooth shading & terminal specialities

[Ethan M. <merritt@u.washington.edu>]

On Tuesday 09 May 2006 03:52 pm, you wrote:
> I'm sending a sample .ps file with gradient fill for the default palette.
> 
> I calculated the values at 11 equally spaced points and converted them
> into hex numbers, now stored in /data. PostScript terminal currently
> draws 1024 single-color rectangles. Does anyone notice any difference
> in the palette produced by gradient fill and the one produced by 1024
> samples?

Aha.  You are using Level 3 extensions to PostScript.

They are not mentioned in the PostScript Language Reference Manual 
(2nd Edition) that I have on my shelf.
Your test file displays on my older machines, which surprises me,
but the result looks truly awful.  My new machines have a newer gs
installed that does indeed support these extensions.

I guess I should go out and buy a new copy of the Language
Reference Manual.

If we were to adopt this approach, we would have to wrap it in a test
for level capabilities so that Level 1/2/3 devices would all do 
something reasonable.  That is certainly possible, but could be done
more easily by an expert.  Harald Harders and I muddled our way 
through something similar for the pattern-fill support, which is a
Level 2 extension, but it was a struggle.

> > OK.  How about PDF, does that have more features like gradient fill than does P.S.?
> 
> PS *does have* gradient fill.

Sufficiently new versions of it [Level 3].

> OK. Let me try to explain, For drawing the "plotting area" in this
> image (http://gnuplot.sourceforge.net/demo_4.1/pm3d.8.png), which is
> nothing else but a bitmap image, gnuplot calls my terminal
>     term->set_color(...)
>     term->fillbox(...)
> 49 x 49 times. For bitmap teminal this doesn't really matter, but for
> my terminal it means constructing 49x49 paths and fill each one of
> them separately (bot at compile time of the image and when displaying
> it in GhostView or Acrobat), not to mention aliasing-artefacts (I
> don't know how they are called, but GhostView shows white stripes all
> over the plot). 

Yeah, we know.  That is the down-side of newer versions of gs/gv/ghostview.
They have a bad aliasing bug.  It's a known bug, but even if they fix it
there will be a lot of broken installations for a long time to come.

> This is extremely inefficient. It would be much better 
> if gnuplot would call a routine
>     term->image(49,49, ....)
> The result would be the visually the same (only better since no
> artefacts would occur) and both compiling and rendering would be more
> efficient. If the driver doesn't support "images", it can still draw
> 49 times 49 filled rectangles.

But how does the higher level code tell a driver what to put in those
49x49 boxes?  In the general case each one has a different color, so
I do not see how you end up saving anything.

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle WA