Re: TreeView: set_fixed_height_mode v TREE_VIEW_COLUMN_FIXED

["Dr. David Alan Gilbert" <gilbertd treblig org>]

* Kristian Rietveld (kris gtk org) wrote:
> On Dec 27, 2009, at 1:48 AM, Dr. David Alan Gilbert wrote:
> > COLUMN_FIXED seems to be defined as 'Columns are a fixed numbers of pixels wide.'
> > but what has that got to do with height?
> 
> The COLUMN_FIXED setting is more about what should happen with the
> width of the column in response to changes in the model.  The main point
> is that with fixed height mode, we speed things up by not measuring the
> size required for a cell and its attributes to draw itself; instead we
> assume a fixed height.  Because we don't measure at all, we also do not
> measure width.  This renders the COLUMN_AUTOSIZE unusable, as well as
> COLUMN_GROW_ONLY (we would have to measure a row as soon as it is added
> (even when it is not visible), but we don't do that).  We are left with
> the FIXED option.

> FIXED does not mean fully fixed; a FIXED column can be set to be resizable by the user of the program.
> 
> A solution for the future will be to sample the widths of a set of rows/columns.  This will be an additional mode, as it does not comply with the strict rules for AUTOSIZE/GROW_ONLY.

The other way to look at this is instead of asserting when you find a
colume that isn't marked fixed, then you just measure those rather than all cells.
That way you don't need any new modes anywhere as far as the API is concerned.

> > In this case there is a big treeview with a thousand rows or so,
> > all the same height but where the width of at least one of the columns
> > varies - this doesn't sound an uncommon situation, but is causing
> > call backs for ~5000 data functions for every cell in the tree
> > on every redraw.
> 
> On a redraw, only the data functions for cells that are visible on the screen should be called.  5000 calls to data functions seems unlikely to me.

I'm not sure, but I think the problem is that until you've measured
all the rows above you, then you can't be sure what it is that's
currently visible.

Dave
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