Re: Printing lines, shapes and pixmaps from a gnome canvas

[Jean Bréfort <jbrefort wanadoo fr>]

Chema Celorio wrote:

> I'd like to give my take on the idea of printing a Canvas.
>
> [I'm not sure if Michael Meeks will remeber this, but the "Printing a
> canvas idea" was the first conversation he and me had while in Paris
> during Guadec 1 in the HelixCode Boart party.]
>
> 	A number of people have talked about this a number of times. I am
> unsure if this will solve a real problem or not, but I have not yet
> found a good scenario where this would be really the best solution. I'm
> not saying there isn't such a scenario, I belive that there is a big
> chance of me being wrong about this, just that I have not yet found it.
>
> 	Complex applications that want high quality printing are going to have
> to tweak with great detail the print output. The rules for displaying
> something on the screen where you have pixels and on printing where you
> dealing with vectors is a different problem.
I am not sure it is so different in the case of the canvas. For example, 
when drawing lines, one  can give the line width in units or in pixels. 
In the first case, the difference between displaying on the screen and 
printing is hidden in the appropriate canvas function. The canvas is 
essentially used for vectorial drawing.

> 	Gnumeric and Evolution fall on this category, I don't this apps
> benefiting from a canvas that can print itself. The way you display an
> email message on the screen is different from how you want it to look on
> the print out, same for a calendar, the calendar printing in evolution
> looks nothing like how it looks on the screen. Gnumeric will also not
> benefit from this, Jody has tried sharing the code used for printing and
> for displaying in the screen, and from what he has told me having two
> separate code paths that are very similar and are kept in sync is the
> best way to go.
>
> 	On top of how you want things to look, the screen has an infinite
> display area, you can scroll over this area all you want, think about an
> email, a spreadsheet or a calendar. On the screen you don't have to
> think about spliting things up, and making pages out of it. You have
> items that might have to print in two pages for example, all this logic
> needs to be defined somewhere, a problem that is not solved by the code
> that displays things on the screen. This does not hold true for apps
> like sodipodi or abiword where there is a page concept.
>
> 	For apps that don't need high quality printing or WYSIWYG, you want to
> make the print code as simple as possible. I'm thinking about things
> like gedit or ghex. On gedit you have a text buffer, that you want to
> print, which the GtkTextView item knows how to deal with, when you print
> the text file the logic is different than the one the widgets uses,
> because it is simpler to do that way, same holds true for that said, I'm
> not trying to imply that I don't want 	Apps that don't require	
The pagination problem is probably the most important. The canvas cannot 
decide internally where a new page begin. So what I am writing will be 
mostly usefull for little applications which do not need more than one 
page. Nonetheless, it is possible to create a canvas, fill it with the 
items which are on the page and print it without displaying on the 
screen (I tried that and it works).

> I am not trying to say that this is not something I would not be
> willing to put in gnome-print or that it should not be written. It might
> be the case that nobody is using something like this simply because it
> doesn't exist. And if so many people have thought that it would be a
> good idea (including myself) it must be for a reason.
It should not go in gnome-print but in libgnomecanvas (IMHO).

> 	The only thing that I'd like to see, is if this code was developed as
> part of an application or developed somewhere where it is getting real
> life usage before putting it in a library.
I developped this code for use in GChemPaint. If it is not included in 
an official library I'll include a special canvas version with just what 
I need in future versions. Current code is based on libgnomecanvas2.0.5 
and is available at 
http;//jean.brefort.free.fr/info/libgnomeprintablecanvas.tar.bz2 (I 
already indicated that in preceding responses in this thread but these 
where never delivered; it seems I have a problem with the mail).

Best regards,
Jean Br�rt