Re: [Pythoncad-developer] Draw in oo mode

[Gertwin G. <ger...@gm...>]

Hi Paolo,

I think your ideas about surfaces are interesting.
This is how I see this subject, correct me if I am wrong.

As you said the boundary of the surfaces are made up from simple
linear entities or circles, ellipses.
We need functions to create and manipulate simple linear boundary entities.

A single boundary entity can serve as edge between 2 surfaces, moving
this single entity modifies 2 surfaces.
Because entities can act as a boundary between multiple surfaces,
these boundary entities itself can not identify the surface object.
For instance a single line entity can act as the boundary between the
street and a building, this line can not say anything about the
surfaces to the left and right. You need to have a kind of way to
describe the surface.

On the other way not all linear entities can act as an boundary for surfaces.
If you have an floor with an table, the table must not result in an
island on the floor.
So the boundary of the table is not used for the floor.

I think all the actions on surfaces (or polygons) that you describes
are handled by the GEOS (http://trac.osgeo.org/geos/) project.
See the methods of the GEOMETRY object:
http://download.osgeo.org/geos/doxygen/classgeos_1_1geom_1_1Geometry.html.

I agree with you that we need a good set of functions to describe
surface objects.
Matteo and I had some discussion about this a while ago.

Besides only surfaces, a cad drawing must contain simple linear
entities, for instance lines can make up a sewerage system, by binding
properties to this line like diameter and material it becomes an
(linear) object.

Regards,
Gertwin


2010/5/15 Paolo Zambetti <zam...@gm...>:
>
> Hi developers,
>
> Let read the follow idea!
>
> Some days ago I bring my chief a draw, and he told me: “next time it’s
> better if you bring me a white paper with some random lines on it, so I
> can fix them on it!”. All times I mind about a list of entities in a
> document I ask myself: Now who does fix them?
>
> All you know everything about the difference between procedural
> programming and object oriented programming. And no matter, it is most
> useful the second one. Then, why we draw in procedural mode instead of
> oo mode?
>
> Geometric entities in a draw are the same as the lines in a printed
> program. Even less complex ones. In fact if I change the order in a
> printed code line in a program the program won’t even start, instead if
> I change the order of the entities in a draw nothing wrong happens. The
> entities in a drow are free from semantics and structure!
>
> All of us think about 3D drawings as special ones because of are visual
> and recognizable. But 3D drawing is special because the designer build
> and handle objects, and the computer software manage them easily.
>
> If you want to do it in 3D you don’t need to do it. You can build,
> handle and manage objects even in 2D environment. The geometric entities
> are 1D objects in a 2D environment.
>
> The objects we can handle are 2D surfaces in a 2D environment. The
> surface is the result of a 1D entity closed frame. I mean “frame” as a
> chain of entities: the end point of an entity is the starting point of
> the next entity.
>
> In a surface you can describe an inside or an outside, a filled side or
> an empty side. And you can have a function applied to the surface. You
> can have a hole on a surface. Even you can hide a surface on others and
> sketch the shadow on it. You can link two surfaces, intersect, add or
> subtract each others.
>
> The final result of all these functions is the projection (view) of the
> physical object, and you can relate it with other projection of the same
> object.
>
> The projections are positioned on the sheet and dimensioned. You can’t
> handle 1D entities outside a surface because if you do it you would
> create a non sense. The designer just have to mind about draw surfaces
> instead of draw random entities.
>
> You can do even more
>
> Each function own the tree of functions who generate it. You can
> generate a function and figure again it’s projection. You can even
> change the input surfaces of the functions and figure again it’s
> projections. The surfaces  patterns may be parametric, I change one
> parameter and figure again the relative projection.
>
> One projection may be set in relation to the others. In this way if you
> move or change the projection even the son projections move or changes.
>
> It’s a new world!
>
> Why do we go on as usual and manage a simple list of entities?
>
>
>
> Best regards..
>
> Paolo Zambetti
>
>
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