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Re: Any use as a general-purpose canvas?
by Tim Jansen on Tuesday 16/Sep/2003, @14:03
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I hate to tell you this, but I never claimed something else :)
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Re: Any use as a general-purpose canvas?
by John Allsup on Friday 19/Sep/2003, @03:21
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Yes, Postscript uses a vector model. BUT, once you have drawn something, you cannot change it. For example
100 100 moveto 200 200 lineto stroke
will draw a line. You cannot give this line a name and change its coordinates later, as with SVG objects. Once the stoke command is given, the line if final. If, on the other hand, you just give the PS interpreter
100 100 moveto 200 200 lineto
then nothing at all will be drawn, and a newpath command will cause the PS interpreter to forget it entirely.
That is what is meant when the previous poster said that the vector model is not stored. (It isn't: only the display bitmap is stored, unless you have a DSC PS file and a device that handles the DSC stuff, but that isn't strictly part of the PS interpreter, and is certainly nothing to do with the PS display model.)
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Re: Any use as a general-purpose canvas?
by James Richard Tyrer on Friday 19/Sep/2003, @07:53
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Thank you for explaining what I and/or the previous poster didn't understand.
However, what you say doesn't quite make sense to me.
I think that what you are doing is confusing the lack of a WYSIWYG PostScript editor program with the language used in a PostScript file. If such a program existed, it would clearly have some of the same capabilities as Sketch or Sodipodi, and it would output a PostScript file, not a bit map.
OTOH (IIUC), SVG stores more information than just the strokes and fills -- it stores information that several of these primative objects go together to make a more complex object, this is an advantage of SVG over PostScript for this use. IIUC, this is what is meant by the vector model. PostScript would need to use comments to do this and this would not be very elegant.
However, Cairo *does* appears to be an attempt to integrate PS, PDF, and screen rendering. I see nothing specific about a native file format for it. But I would assume that it will be XML with embedded SVG. In that case, it would be able to export to PS and PDF but not use them as input, or if useable as input then an export and reinport would result in the loss of information.
--
JRT
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Re: Any use as a general-purpose canvas?
by Tim Jansen on Friday 19/Sep/2003, @09:12
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>>Cairo *does* appears to be an attempt to integrate PS, PDF, and screen rendering. I see nothing specific about a native file format for it. But I would assume that it will be XML with embedded SVG. In that case, it would be able to export to PS and PDF but not use them as input, or if useable as input then an export and reinport would result in the loss of information.<<
Cairo is just a renderer that happens to have a X11 extension and is integrated in the X11 server. You call a few C methods, and it will paint something. Usually it will paint on the screen, but with the right driver it may print to PS or PDF stream.
It can not load or save data, and it does not know anything about XML. It does not know anything about PS or PDF either.
PDF rendering model refers to the type of commands that it processes. There are different ways to describe vector graphics, and Cairo happens to go the Adobe way.
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