gEDA: gEDA-dev: picture png support

[Carlos Nieves Ónega <cnieves@xxxxxxxxxx>]

Hi Ales,
moving this thread to geda-dev with a better subject...

El dom, 09-10-2005 a las 19:57 -0400, Ales Hvezda escribiÃ:
> >It's in relation with adding picture output support when exporting png.
> >In order to do that I think it's better to use gtk functions to get a
> >pixmap of the drawing area and then save it as a .png file. This way we
> >can get rid of libgdgeda... (I think it's not used for anything more).
> >It's like a preview picture of the schematic in memory, and this will be
> >needed when using the file load/save gtk dialog...
> >I made some tries to get a pixmap from the drawing area, but I was not
> >quite succesfull. Anyone can give me a clue about how to do this?
> 
> 
> 	Ah, yes, in order to do this you need to look at the gdk routines
> which render into pixbufs and drawables:
> 
> http://developer.gnome.org/doc/API/2.0/gdk/gdk-Pixbufs.html
> 
> More specifically you should look at:
> 
> http://developer.gnome.org/doc/API/2.0/gdk/gdk-Pixbufs.html#gdk-pixbuf-get-from-drawable
> 
> In libgeda/gschem the:
> 
>   GdkWindow *window;
> 
> and 
> 
>   GdkPixmap *backingstore;
> 
> are the primary drawables.  Once you get the data into a pixbuf, you can use:
> 
> http://developer.gnome.org/doc/API/2.0/gdk-pixbuf/gdk-pixbuf-file-saving.html
> 
> the various routines for saving pixbufs to files. 

I got pixmaps from GtkWidget *window and backingstore, but they are only
pixmaps of the same area displayed in the gschem's window (which is not
right if you are only displaying a small area of the schematic)... and I
got best results from backingstore (I mean other visible windows in the
desktop can affect the png output when using GtkWidget *window, I
think). Is backingstore cleaner than GtkWidget *window?
Is there any other variable storing the full gschem's window? If not, I
guess I need to do a 'zoom extents' before getting the pixmap, get the
pixmap, and then restore the previous zoom factor (without the user
noticing all these, of course)...

> I think that getting rid of libgdgeda is a great idea, but if we are going
> to do that, we have to make sure we can do all the rendering without creating
> a gui window etc... otherwise we are no better than the (my) existing (lame) 
> implementation for creating pngs.  

I think it's not so simple. I will get picture png support working
first...

The problem is that, for example, you need a visible window before
setting the gc of the window, which is done when initializing the main
window... I think we need to split non-gui functions and gui functions,
and call the latter only when needed.

Cheers,

Carlos
-- 
Carlos Nieves Ãnega <cnieves@xxxxxxxxxx>