Re: Custom Extensions to new Shapes

[Hans Breuer <hans breuer org>]

At 17.09.2012 14:25, Dave Johnston wrote:
> It would be great if the XML used to create shapes could be extended to
> support a few other types.
> I think most cases could be catered for if the following was available
> (maybe it already is and I haven't seen it)
Tne suggested functionality would certainly but useful, I'm pondering the 
idea to make more use of the Dia "StdProps" type system from custom shapes 
for a while, but am not aware of any code written to actually do that.

> Enums and Composite Types - i.e. something along the lines of
>
> Enum:
> <ext_attribute name="DayOfWeek" type="enum">
> <value type="string">MON</value>
> <value type="string">TUE</value>
> <value type="string>WED</value>
> </ext_attribute>
>
> This would be represented as a drop down box on the attributes page.
Having names and values independent would give a better fit to what's 
already there. See lib/prop_inttypes.[hc] - EnumProperty for the basics.
Grep PROP_TYPE_ENUM for actual uses. You would not have to write any new 
user interface just provide the right PropDescription.

> Composite Type:
> <ext_attribute name="Date" type="composite">
> <attribute name="Day" type="int"/>
> <attribute name="Month" type="string"/>
> <attribute name="Year" type="int"/>
> </ext_attribute>
>
> This would be represented on a single line like this (obviously with
> current values subsidised):
>
> ______________________________
> |Day: 17 | Month: Sept | Year: 2012 |
> |_______|___________|__________|
For this I'd suggest to add a new type 'date', which would use GtkCalendar 
for it's widget. Should maybe use GDateTime for the backend - although that 
would require to bump the minumium GLib version.

The general composite case migh still be useful, but doing a good and 
compatible automatic user interface for it might be hard. The default 
representation in property dialogs is
        Description : Widgets
see the recently added MatrixProperty for a bad example having more than 
one widget ;-)

> Are there any plans do add this kind of functionality? If not could anyone
> suggest what files I would need to start looking at to add support for the
> enum type at least ? I've been looking at custom_object.c, but still trying
> to figure out how all the attributes are parsed and the resultant data is
> drawn to screen.
custom/shape_info.c should do the translation from XML to PropDescription 
(it currently does so by calling custom_setup_properties()). For the enum 
type and other PropDescription::extra_data has to be filled. For enum it is 
a vector of PropEnumData, see e.g. prop_std_text_align_data in properties.h.
For other types it would also be useful to fill these to eg. define upper 
and lower limit.

custom/custom_object.c should just contain code to merge PropDesciptions in 
custom_describe_props(); maybe also modify custom_get_props() and 
custom_set_props() to split the given properties between existing struct 
_Custom fields and extended properties.

There is a flaw in the current implementation of custom_setup_properties() 
but I would to think more about it to suggest a fix.

HTH,
        Hans

-------- Hans "at" Breuer "dot" Org -----------
Tell me what you need, and I'll tell you how to
get along without it.                -- Dilbert