Re: pango: layout proposal

[Behdad Esfahbod <behdad behdad org>]

Hi,

On 10/23/2009 12:42 PM, Ilia wrote:
> Dear Sir.
>
> Please excuse me for writing you directly. I am new to the open source
> world, and do not know how it is usually done.
>
> I want to switch our applications from GDI to Pango and Cairo because
> these excellent libraries have many advantages. Currently, building
> Pango layouts assumes equal space for all lines in the layout, which in
> reality is often not the case. E.g. we generate a multi-page report, and
> next page may have different space for the text flow. Currently, we
> would have to find the first line which does not fit the page, and then
> create layout for the next page, which causes text reallocation and
> makes the cursor navigation over the lines more difficult. The situation
> will become more complex if the text must flow around images.

*If* all lines have the same width, the way you do this is to walk the layout 
using a PangoLayoutIter and render each line whereever you wish.



> It would be much more convenient, if we could adjust space width/height
> and continue existing layout with a new box without text reallocation
> and keeping the continuous cursor navigation.

Sounds like this bug:

  http://bugzilla.gnome.org/show_bug.cgi?id=435706

Can you comment on the bug?


> Another problem is ellipsizing paragraphs separately instead of per-box
> basis. A beautiful solution would be if a function, which would allow us
> ellipsizing the the last successfully-composed box explicitly, when we
> find that the next box cannot be allocated.
>
> Also, I was not able to find the answer on the following question. When
> drawing a layout to a target cairo context, we must call
> pango_cairo_update_layout() or the pair pango_cairo_update_context() +
> pango_layout_context_changed() if the context is shared. This would
> cause recalculation of the layout with repositioning glyphs and possibly
> adding/removing ones in case of wrapping/ellipsizing. But how can I
> compose everything to a printer and show it on a display even if it will
> not look as nice as rendering to the display naturally, but would place
> the glyphs exactly where they are expected?

pango_cairo_update_layout() calls pango_cairo_update_context() +
pango_layout_context_changed().

To get device-independent positioning, turn metrics hinting off in your cairo 
font options.  There are a couple known bugs around this, but this should work 
if you don't use cairo_scale().

behdad

> Thank you for your superior work.
> Ilia