Design question

[everguet@gmail.com]

Hi,

I have a small question about design, implemented in C++ of course ;)

I have a set of objects A, B and C, which are pure C++ code (no GUI,
I/O, ...). I need to draw them on screen (using OpenGL), but i don't
want to put my OpenGL methods in my class A, B and C.

How can i do that ? Using an aggregate object member of my class, using
derivation, ... ?

Thanks.

[Marcelo Pinto]

Re: Design question


everg...@gmail. com escreveu:
[color=blue]
> Hi,
>
> I have a small question about design, implemented in C++ of course ;)
>
> I have a set of objects A, B and C, which are pure C++ code (no GUI,
> I/O, ...). I need to draw them on screen (using OpenGL), but i don't
> want to put my OpenGL methods in my class A, B and C.
>
> How can i do that ? Using an aggregate object member of my class, using
> derivation, ... ?
>
> Thanks.[/color]

In order to isolate your logic from the specifics of OpenGL I would
create a layer (drawing layer) of classes that would know how to draw
your objects and would let a controller class coordinate the drawing
passing to the drawing layer the objects to be drawn.

HTH,

Marcelo Pinto

[Gernot Frisch]

Re: Design question


<everguet@gmail .com> schrieb im Newsbeitrag
news:1138715369 .364617.107700@ g47g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> I have a small question about design, implemented in C++ of course
> ;)
>
> I have a set of objects A, B and C, which are pure C++ code (no GUI,
> I/O, ...). I need to draw them on screen (using OpenGL), but i don't
> want to put my OpenGL methods in my class A, B and C.
>
> How can i do that ? Using an aggregate object member of my class,
> using
> derivation, ... ?[/color]

class TRIANGLE
{
float xyz[3][3];
};

template <class CData> class GLDrawObject
{
virtual std::vector<TRI ANGLE>* GetTriangles() = 0;
};

class A
{
std::vector<TRI ANGLE>* GetTirangles()
{
yaddayadda;
}
};

Just my .02$

[everguet@gmail.com]

Re: Design question

Thanks, but i want to avoid a big switch case with all my object types
in this layer. This is what you mean ?

[Marcelo Pinto]

Re: Design question


everguet@gmail. com escreveu:
[color=blue]
> Thanks, but i want to avoid a big switch case with all my object types
> in this layer. This is what you mean ?[/color]

No it is not. If you fall in that situation you could use some factory
and some hierarchy on the OpenGL side or you could use templates to
parameterize the processing. But without seeing some code it is
dificult to understand the exact problem you are facing.

HTH,

Marcelo Pinto

[Emmanuel V.]

Re: Design question

I am on the design phase, no code for the moment ;-)

[Jim Langston]

Re: Design question

<everguet@gmail .com> wrote in message
news:1138715369 .364617.107700@ g47g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> I have a small question about design, implemented in C++ of course ;)
>
> I have a set of objects A, B and C, which are pure C++ code (no GUI,
> I/O, ...). I need to draw them on screen (using OpenGL), but i don't
> want to put my OpenGL methods in my class A, B and C.
>
> How can i do that ? Using an aggregate object member of my class, using
> derivation, ... ?
>
> Thanks.[/color]

Consider deriving from a base that does the openGL calls for you. If at
some point you switch to, for instance, DirectX you would only have to
change the base class. In theory.

[JustBoo]

Re: Design question

On 31 Jan 2006 05:49:29 -0800, everguet@gmail. com wrote:
[color=blue]
>I have a set of objects A, B and C, which are pure C++ code (no GUI,
>I/O, ...). I need to draw them on screen (using OpenGL), but i don't
>want to put my OpenGL methods in my class A, B and C.[/color]

Some good suggestions here. You might also consider the newsgroups
below as they are populated with people who solve OpenGL problems
on a daily basis.

comp.graphics.a lgorithms
comp.graphics.a pi.opengl

What I did was basically wrap various OpenGL functions and sequences
of functions into a few "stand alone" classes. I then called these
from my GUI classes. I had reduced what could have been many calls to
OpenGL "all over the place" to a few simple calls to the OpenGL
classes. To pull those out and replace them with DX calls should be
easy if it ever happens. (Which it won't as long as I breath. :-) ).

A downside to this was I had created a tight coupling between my gui
classes and the OpenGL classes. This was by design though. I created
the whole "thing" to be a subsystem along the lines of the Facade
pattern.

HTH

[Dave Townsend]

Re: Design question


<everguet@gmail .com> wrote in message
news:1138715369 .364617.107700@ g47g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> I have a small question about design, implemented in C++ of course ;)
>
> I have a set of objects A, B and C, which are pure C++ code (no GUI,
> I/O, ...). I need to draw them on screen (using OpenGL), but i don't
> want to put my OpenGL methods in my class A, B and C.
>
> How can i do that ? Using an aggregate object member of my class, using
> derivation, ... ?
>
> Thanks.
>[/color]

I've solved this type of graphics problem a number of times by using a
Visitor Pattern in conjunction with the Composite Pattern. The visitor
derived object then can take care of the particular graphics system outside
of the classes A, B, or C.

[Emmanuel V.]

Re: Design question

I will have a look to those patterns, thanks ;)