Re: GtkSpreadTable ('spread-table' branch)

[Tristan Van Berkom <tristanvb openismus com>]

On Fri, 2010-10-08 at 14:08 +0200, Murray Cumming wrote:
> On Fri, 2010-10-08 at 20:36 +0900, Tristan Van Berkom wrote:
> > On Fri, 2010-10-08 at 12:13 +0200, Murray Cumming wrote:
> > > On Thu, 2010-10-07 at 12:37 +0900, Tristan Van Berkom wrote:
> > > > Hello list again,
> > > >    Now for the introduction of GtkSpreadTable (still open for
> > > > a better name for this widget).
> > > > 
> > > > What the spread table container does is takes a linear list
> > > > of widgets, which can be of variable size and spread/distribute
> > > > the widgets as evenly as possible according to their size
> > > > across a fixed number of rows or columns. Thus requiring the
> > > > smallest size possible while maintaining the fixed number
> > > > of columns or rows.
> > > > 
> > > > For instance when oriented vertically, widgets will be listed
> > > > top-down with the first widget in the top-left corner and the 
> > > > last widget on the bottom right; widgets will be lined up in 
> > > > such a way to require the least height as possible.
> > > > 
> > > > This widget is the one that actually meets the requirements 
> > > > for Glom[0].
> > > > 
> > > > To get a better idea of how this works you can checkout and 
> > > > build the 'spread-table' branch I added to GTK+ yesterday... 
> > > > fire up the ./tests/testspreadlayout demo.
> > > 
> > > Some quick links might be helpful
> > > http://git.gnome.org/browse/gtk+/log/?h=spread-table
> > > http://git.gnome.org/browse/gtk
> > > +/tree/gtk/gtkspreadtable.h?h=spread-table
> > > 
> > > I have already wrapped this in a branch of gtkmm, and even used it in
> > > Glom instead of my custom code. It seems to work fine for me.
> > > 
> > > Some small suggestions:
> > > 1.
> > > I think lines should be lines_count.
> > > 
> > > 2.
> > > I'd like a get_widget_line(GtkWidget*) function so I can discover what
> > > line (column in my case) the widget is currently in. I'd like to query
> > > that whenever the allocation changes, so that I can align some child
> > > widgets (children of HBoxes in columns of the GtkSpreadTable) via a
> > > GtkSizeGroup. Obviously I only want widgets in a GtkSizeGroup (so they
> > > have the same width) that are in the same column.
> > 
> > I suppose they could even be read-only child properties,
> > in this way we could cache the current line number and 
> > notify the changes when one widget gets placed on an new line
> > (an unallocated widget would always be on line -1).
> > 
> > Then you could just watch when the widget jumps from line to line.
> > 
> > However I wonder if changing some if the internal widget's size
> > groups may effect the overall requested width of that column...
> > and in the worst case you end up with a situation where:
> >   - Allocation happens
> >   - Change size groups in consequence
> >   - Size group changes widget requests
> >   - Widget's get reorganized into different
> >     columns as a result of the new size-grouping. 
> > 
> > Maybe it wont happen so long as you are playing with smaller
> > sizes, but it may be recommendable to just size group widgets
> > in all columns equally (I suppose experimentation will tell).
> 
> Yeah, I saw the risk of an endless loop, but maybe I can prevent that in
> my code. Or maybe it will just be one extra relayout. My existing code
> actually has a hard-coded concept of two horizontally-aligned items in
> each column, so it knows about that constraint already. But that's very
> specific behaviour.
> 
> Alternatively, is there just some way to find a child GtkWidget's
> position in a GtkContainer? Then I wouldn't need extra API.
> 

You can use gtk_widget_translate_coordinates() for that... but it 
will leave you with alot of guessing (observing widget allocation
sizes in the child list etc).

I think an API will make your code much cleaner, maybe it would
help if at least you got to step in /before/ the allocation
actually happens.

i.e. the same API could be:

guint gtk_spread_table_get_child_line (table, child, size);

where it would return: the column 'child' would fall into
if 'table' were allocated 'size' width.

This could potentially give you a chance to shift size groups, 
run some tests with the above api and then actually allocate
the table's size after you know it's safe.

Just a thought,
   -Tristan