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Re: how do I create an image file from an object graphics window? [message #40244 is a reply to message #40101] Fri, 23 July 2004 09:28 Go to previous messageGo to previous message
Karl Schultz is currently offline  Karl Schultz
Messages: 341
Registered: October 1999
Senior Member
"Haje Korth" <haje.korth@jhuapl.edu> wrote in message
news:cdqth5$qro$1@aplcore.jhuapl.edu...
> Holger,
> I have used 'idlgrclipboard' object in the past, which can create
Postscript
> file. However, the implementation in 6.0 is still buggy. 6.1 will be
better,
> there may still be some issues with alpha blending. Any way, if your
> view/scene is not too complicated it may work for you. A note on the side:
> It amazes me that RSI worked out so many details on making object graphics
> look pretty and totoally forgot to spend the time working on creating
> descent quality output of the graphics. In order to get what I want, I
have
> to write every code twice, once in object graphics for the screen and then
> use direct graphics techniques to create the PS file. Not very
> efficient.....

Remember that the clipboard has both bitmap and vector modes. The bitmap
mode captures the contents of the scene exactly as you would see it on the
screen. You can also do pretty much the same thing by getting the data out
of the grBuffer and grWindow objects.

Yes, vector output in 6.1 is quite a bit better, but we still need to
understand that vector output cannot possibly recreate all the graphical
features that you might use on the display. Vector output systems (e.g.,
PostScript, Windows metafiles) are not really "3D" in any way, while Object
Gaphics obviously is a 3D system. It's difficult to map a system with high
capabilities onto ones with lesser capabilities. For example, vector
systems do not have depth buffers. IDL does a crude depth sort in vector
output to approximate the effect of a depth buffer, but it won't sort things
out completely. Similar restrictions apply for things like alpha blending.

One of the main motivations for Object Graphics vector output was to reduce
the size of the graphics output. In bitmap mode, even a simple plot with a
few dozen lines and some text would require several MB of space, depending
on the dimensions of the drawable, which seems silly when there is so little
data actually in the plot. With vector output, the same data can be
represented with a few dozen line plot commands and some text strings, which
adds up to a PostScript file of 1K or so in length So vector output can be
a big win when working with plots, charts, and other visualizations that are
more "2D" than "3D" and don't use a lot of advanced rendering features.
Bitmap output is better when you need to preserve all those "3D" qualities.

Karl
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