Re: Saving a gnomecanvas to a .png (or other graphic format)

[Jean Bréfort <jean brefort normalesup org>]

Le samedi 12 mars 2005 �3:09 -0800, Steve Field a �it :
> I have been successfully (for the most part) been
> using gnomecanvas to do a flight sim instrumentation
> type display. What I'd eventually like to do is make a
> demo movie of the display.
> 
> To that end, I've been trying to dump any updated
> gnomecanvas to a .png file for later manipulation into
> a .mng or animated .gif or mpeg file. To date, I've
> been unsuccessful.
> 
> I dug into the list archives and found a post that
> seemed to indicate that I could copy the code from
> gnome_canvas_paint_rect to copy the gnomecanvas into a
> pixmap which could then be copied into a pixbuf for
> .png saving. I dutifully copied code and got a .png
> file that's the right size, but might have the wrong
> depth since the colored portion of the resulting .png
> looks like a smeared and shortened version of the
> original gnomecanvas.
> 
> I added the following code to the end of my
> gnomecanvas update routine (canvas2 is a pointer to
> the GnomeCanvas of interest):
>     {
>         GnomeCanvas *canvas = GNOME_CANVAS(canvas2);
>         GtkWidget   *widget = GTK_WIDGET(canvas2);
>                                                       
>                                                       
> 
>         GError *gerror = NULL;
>                                                       
>                                                       
> 
>         // Make a temporary pixbuf
>         GdkPixbuf *pb = NULL;
>                                                       
>                                                       
> 
>         // Make the "temporary" pixmap
>         GdkPixmap *p = gdk_pixmap_new
> (canvas->layout.bin_window,
>                                       
> widget->allocation.width,
>                                       
> widget->allocation.height,
>                                       
> gtk_widget_get_visual (widget)->depth);
>         // Draw the root canvas item to the pixmap
> GdkDrawable
>        
> (*GNOME_CANVAS_ITEM_GET_CLASS(canvas->root)->draw)
>                 (GNOME_CANVAS_ITEM(canvas->root),
>                  GDK_DRAWABLE(p),
>                  0,0,
>                  widget->allocation.width,
>                  widget->allocation.height);
>          // Now put the pixmap into a pixbuf
>          pb = gdk_pixbuf_get_from_drawable(NULL,
>                                            p, NULL,
>                                            0,0,
>                                            0,0,
>                                            -1,-1);
>          if(pb==NULL){
>              g_print("Problem rendering from the
> pixmap into the pixbuf\n");
>          }else{
>              if(!gdk_pixbuf_save(pb,
>                                  "blah.png",
>                                  "png",
>                                  &gerror,
>                                  NULL)){
>                  g_print("Problem saving the pixmap to
> a .png file\n");
>              }
>          }
>     }
> 
> BTW, thanks to Mr. Pennington for his excellent GGAD
> which got me this far!
> 
> Thanks for any thoughts or ideas!
> 
> Steve Field

I do that in GChemPaint to draw a GnomeCanvasGroup to a pixbuf:

GnomeCanvasGroup *group;
ArtDRect rect;
...
/* initialize group to canvas->root or another group and rect to the
area you want to draw */
...
GdkPixbuf *pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, w, h);
GnomeCanvasBuf buf;
buf.buf = gdk_pixbuf_get_pixels (pixbuf);
buf.rect.x0 = (int) floor (rect.x0);
buf.rect.x1 = (int) ceil (rect.x1);
buf.rect.y0 = (int) floor (rect.y0);
buf.rect.y1 = (int) ceil (rect.y1);
buf.buf_rowstride = gdk_pixbuf_get_rowstride (pixbuf);
buf.bg_color = 0xffffff;
buf.is_buf = 1;
(* GNOME_CANVAS_ITEM_GET_CLASS (group)->render) (GNOME_CANVAS_ITEM
(group), &buf);
gdk_pixbuf_save (pixbuf, filename, type, NULL, NULL);
g_object_unref (pixbuf);