[GRASS-dev] Display library documentation?

[Vaclav Petras]

On Tue, Sep 15, 2015 at 6:06 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

> On 14/09/15 15:53, Vaclav Petras wrote:
>
>> Hi,
>>
>> is there some documentation on how to use the display library, i.e. how
>> to write a d.* module?
>>
>
> I imagine you looked at
> https://grass.osgeo.org/programming7/displaylib.html ?
>
>
> I've tried reading d.vect code but I miss the
>> general rules and concepts like how to set color or which coordinates
>>
>
> Have you checked display_shape() in shape.c and the individual display_*
> functions in the relevant files (area.c, line.c) for the different types of
> features ?
>
> The color is set with D_RGB_color which takes a color struct as input.
> Then the feature is drawn with D_polygon_abs/D_polyline_abs/D_polydots_abs
> which take the coordinates from the line struct Points which is filled with
> info using Vect_read_line().
>
> should be used when as well as information which functions should be
>> used in which case like what is the difference between D_symbol and
>> D_symbol2.
>>
>
> From the programmer's manual section on D_Symbol2:
>
> "The same as D_symbol(), but it uses a primary and secondary color instead
> of line and fill color. "



Thanks Moritz, this is approximately as far as I got. I hoped I over looked
something but apparently not. The documentation is in Doxygen format but it
is just a list of functions. What is primary and secondary color, I can
only guess from context, etc. and your sentence about feature drawing is
the most detailed documentation we have now for the display library.

So, I think that we have a big problem. It seems that the display library,
despite its crucial role, is the most underdocumented library we have. In
fact it is not documented at all. Others have some readmes with basic
workflow, comments for functions or comments in code. Display library has
nothing. Because of the level of abstraction for different drivers, its
hard, at least for me, to guess the rules or even best practices for usage
and because of the complexity or specificity of display modules, its hard
to guess what is the general and effective way of doing things.

Please, can somebody with some experience document some functions, provide
examples or a complete d.example module? When having at least something I
can then help with formatting or examples.

Thanks,
Vaclav
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