Re: [spam score 10.00/10.0 -pobox] Newbie seeks advice (mixing text, widgets, images on a scrollable canvas)

[Havoc Pennington <hp redhat com>]

Pascal Haakmat <a haakmat chello nl> writes: 
> Basically, the application I am trying to write is a browser. That means I
> need to render text, images and form elements onto some kind of canvas, and
> have the entire canvas be scrollable. What I am ultimately looking for is
> the best way to implement this using GTK, but I'll first explain where my
> current hackish implementation breaks down.
>
> Right now, I am using a GtkFixed container widget as my canvas. Text is
> drawn directly onto the GtkFixed container widget and I add form elements
> using gtk_fixed_put().

I would suggest using GtkLayout instead. Unlike GtkFixed, it has an
infinite scrolling area, and you won't need the viewport.

Another suggestion is to look at the source code for the GtkHTML
widget. You can get that from GNOME CVS or ftp.

> The first problem is that I get into endless redraw loops:
>
> 1. I get a "draw" signal for the GtkFixed widget.
> 2. I draw some text.
> 3. I add a form element and show it.
> 4. This triggers another "draw" signal on the GtkFixed widget.
> 5. Go to 1.
>
> What would be the best solution to avoid this loop? Should I render the text
> onto a pixmap and use that as the background for the GtkFixed widget? Should
> I subclass GtkFixed? Should I write my own widget alltogether?

Don't do 3 in a "draw" signal handler. "draw" should just draw.

> The second problem concerns scrolling. Currently, the GtkFixed widget is
> inside a GtkViewport, which is inside a GtkScrolledWindow. What I would
> really like to do is to get rid of the GtkViewport and implement scrolling
> natively in the GtkFixed container widget, but I do not understand how to do
> this. Is it necessary to write my own widget? And if so, do I have to start
> from scratch or is GtkFixed a good place to start at?

Scrolling is much easier with GtkLayout, where you basically just have
to offset your coordinates by layout->xoffset layout->yoffset before
drawing. GnomeCanvas is a GtkLayout subclass, I wouldn't be surprised
if GtkHTML was also.

Havoc