[HOpenGL] Re: [Haskell-cafe] Decoupling OpenAL/ALUT packages from OpenGL

[Tillmann Vogt]

Balazs Komuves schrieb:
>
>
> On Sun, May 3, 2009 at 12:56 AM, Tillmann Vogt 
> <Tillmann.Vogt at rwth-aachen.de <mailto:Tillmann.Vogt at rwth-aachen.de>> 
> wrote:
>
>     Now that you mention it. I just looked through haskell hierachical
>     libraries and there seems to be no standard data types for vector
>     math. Am I getting something wrong or is every library that is
>     using linear algebra stuff using its own data types? So if I use a
>     numeric library for matrices inside HOpenGL I have to convert around?
>
>     I think it would be nice to have data types and functions for dot
>     produkt, scalar product, norms, ...
>     together with HOpenGL types.
>
>     Currently I am trying to embed a triangulation library from a ten
>     year old diploma thesis (http://www.dinkla.net/fp/cglib.html) in
>     my libary (I know that glu has tesselation). The author has
>     developed a quite big and abstract type structure for all sorts of
>     computer graphics algorithms and I didn't wanted to copy this into
>     my library just for triangulation. But it is reasonable. It could
>     be combined with HOpenGL types to maybe
>     Data.VectorMath or Data.LinearAlgebra . I would favour the second.
>
>
> The problem is, in my opinion, that the design space of linear algebra 
> libraries is big and complex;
> thus I don't think a "canonical" linear algebra library is a good idea.
>
> There are at least 4 linear algebra libraries on Hackage already:
>
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmatrix
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vector-space
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Vec
> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vect
>
> and they are all very different, and I can easily imagine the 
> usefulness of some more.
These libraries are different in the way they store data and in the 
interface. vectors-space is abstract, while your library offers an 
easier interface. For example vector-space defines an additive group and 
an affine space while you have a function translate3x.
But essentially they all implement standard algorithms one learns in a 
computer science course (linear algebra, computer graphics) in university.

I think the best would be to have one abstract library. Then hmatrix 
imports this library and overloads the functions.
People who want to use the speedy hmatrix lapack binding import it. 
Importing the original abstract library gives an impression of the speed 
differences.
Then to have your easy interface you reimplement your library by giving 
the user a choice of which library to base it on (the abstract or 
hmatrix). As the last step HOpenGL renames an abstract n-dimensional 
vector (for n=3) to Vertex3 and the I can apply all the useful functions 
to Vertex3 values.

The disadvantage is of course that someone who wants to find out how 
something works has to read through a chain of types in different files. 
But this can be solved with a good documention that blackboxes 
everything that must not necessarily be understood by everyone. I also 
hope that one day a good IDE will help here.
The argument that these libraries are fundamentally different is in my 
opinion not valid. I also don't understand why a too general libary 
would open a can of worms.
Haskell has abstract data types. A Matrix can contain real values or 
polynomials or whatever. A Math person can derive his crazy library with 
overloaded functions. And no one whoe doesn't want to read this has to. 
I also think that most people want to do similar things as can be seen 
by the upper four libraries.

>
> Self-advertisement: The last of the above four is designed especially 
> for graphics use,
> in particular with OpenGL; but I'm not really satisfied with its 
> current state, so feedback
> is very welcome!
>
> Balazs
>