[gl2ps] Clipping and Background

[Christophe Geuzaine]

Joe Miller wrote:
> Hi, 
> 
> I had a quick question about clipping and backgrounds
> with postscript. I see in the example provided how to
> start and end the gl2psViewport so that gl2ps clips at
> the boundaries. However, before you issue the clip
> command you do a fill which clears the background. I
> was wondering if there was a particular reason for
> this or if there was another way I could clip in
> postscript.
> 
> Here's my situation. I setup a viewport in opengl, I
> then open up another viewport on top of the original
> one. I then add some text to the top viewport and some
> of that text falls out of that viewport's range
> (though is clipped by the rasterizer). The text that
> falls out of range is not being completely clipped in
> postscript when I don't set gl2psViewportBegin/End.
> When I set gl2psViewport it clips the text correctly,
> however, the picture on the bottom viewport is cleared
> by the fill. 
> 
> So I was wondering if you had any suggestions (besides
> switching to one viewport) or if it was going to be
> problematic for me if I removed the fill line. 
> 

Hi Joe - Indeed, for PS/EPS output, the current version of GL2PS does 
not clip the viewport if the background is not drawn (that's a bug!). In 
addition, the current version provides no way to disable the background 
for just a specific viewport (that's a shortcoming in the API).

I tried to fix both issues in my CVS tree:

- gl2psBeginViewport() now always clips (even if GL2PS_DRAW_BACKGROUND
is not set)

- there is a new function in the API called gl2psSetOptions() that 
permits to change the options on the fly. You could for example call 
gl2psBeginPage() with options=GL2PS_DRAW_BACKGROUND, and then change the 
options before calling gl2psBeginViewport() in order to disable the 
background drawing for that specific viewport.

The new version is available here:
http://geuz.org/gl2ps/src/gl2ps-nightly.tgz

Let me know if this solves your problem.

Take care,

Christophe



> Sorry for being so long winded. Thanks for the help.
> 
> -joe
> 
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-- 
Christophe Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org