Andre Poenitz wrote:
> On Tue, Oct 21, 2003 at 09:25:46AM +0000, Angus Leeming wrote:
>> Andre Poenitz wrote:
>> >> Is this just a wild flight of fancy, or does anybody else think
>> >> that it's a sensible proposal?
>> >
>> > I think this could be handled on a case-by-case base by using
>> > some helper functions in the insets that really need it.
>>
>> Actually, I did some reading and I think I have stumbled across
>> something very powerful.
>>
>> The C++ streams allow us to define arbitrary new modifiers --- and
>> enable subsequent operations on the stream to be aware of them. For
>> example, the code below would be used
>> std::ostringstream os;
>> os << font::setFamily(font::SERIF) << "Andr? "
>> << font::setFamily(font::SANS_SERIF) << "P?nitz\n";
>
> I know this in theory but never managed to work with that in praxi.
>
> I wanted to transform the different "math output stream" to a scheme
> like that at one point of time but then got distracted somehow...
>
>> Note that it works on existing stream types!!! Thereafter one would
>> need to write a 'decipherer'. For example, something to establish
>> the width of the string in this font, or to paint it, but the
>> beauty is that this 'mark-up' is entirely separate.
>
> Not really, is it?
>
> You just modify some state of the stream (i.e. to "SERIF"). Than
> every write on that stream has to check this state and respond to
> it.
>
> It is not a kind of out-of-band signalling, rather some fancy way to
> add more data room to a stream.
>
> This safes you writing lots of 'operator<<' for the standard types
> like int, double, ... fro your custom streams, but that's it.
> And now you've got some new state in the stream object. It does not
> affect the data buffer at all. This is basically only syntactic
> sugar over
>
> void write(ostream & os, MyObject const &, SomeExtraData const &
> extra)
>
> by combining 'os' and 'extra' and re-using operator<<() for the base
> types.
My main point is that the metrics and draw routines repeat large
blocks of code and that my separating the information from the way it
is used we can only win.
I agree that we need to operate on the resulting data and I openly
admit that I haven't read enough to do that. Perhaps you can help
fill in my knowledge gap?
I imagine something like
int fontWidth(std::ostream & os) {
int width = 0;
std::ostream::iterator it = os.begin();
std::ostream::iterator end = os.end();
for (; it != end; ++it) {
int const family = os.iword(setFamily::getAlloc())
if (family == -1) {
std::cout << "Family data not set\n";
continue;
}
LyXFont font(family);
width += (*it, font);
}
return width;
}
But such a stream would also allow the frontends to implement their
own mark-up. Ie, pass a stringstream to the dialog and get bold and
italic mark up in the right places.
Regards,
Angus
