Re: graphics and OpenGL rendering

[Michael Goffioul]

On 12/24/07, Shai Ayal <address@hidden> wrote:
> Michael, I think this is an excellent idea and fits in with my plans
> perfectly. I have started writing the backend and decided that it
> would be best to split the toolkit part (which in my case is based on
> fltk) which deals with all the OS specific parts, and the generic
> OS-independent OpenGL part which should be just that -- pure OpenGL.
> It would be great to have help (and it sounds like it would be a lot
> of help) in this part -- especially the 3D part which I do not have
> any experience with (octplot is 2D).

My rendering code does not make any difference between 2D and 3D:
it's full 3D code, 2D is just a special case of 3D (view angles are
[0 90]). I think it performs well and can render all Matlab core objects
with a high compatibility. If you agree, it could be a starting point
(once converted to C++).

> I think we could probably end up
> sharing everything but the font rendering for which you do using java
> libraries and I plan to do using FTGL.

Indeed, text rendering will still be toolkit dependent, because it's not
handled by OpenGL directly. However, the idea is usually the same:
render the text into a bitmap and transfer the bitmap to OpenGL.
The main difference is then how the bitmap is generated.

> Some questions remain to be answered:
>
> 1. How will we avoid code duplication -- i.e. we would need a single
> cvs/svn repository. I planned on using octave's cvs. Will that work
> for you?

I don't have a developer access to it, so I would have to send you
patches. But that's not a problem. The code I have for the moment
is still experimental. I defined a graphics_renderer base class that
defines the rendering interface and performs common tasks. The
OpenGL rendering is implemented in a derived class that takes
the octave graphics properties and render them using OpenGL
(this leaves the possibility for other type of renderers). I can send
you the code if you want. The main problems I have for the
moment are:
- octave graphics objects are missing a lot of properties that are
used by my rendering code; I think the best would be to take the
matlab documentation and add all missing properties to the core
objects
- graphics properties are not typed, a lot are simply of type
octave_value, without any distinction on the allowed values;
I guess this will be changed in the near future, but I'd like to
happen it soon as this has an impact on code that should use
those properties

> 2. After this is done, what will be the differences between the 2
> backends? What will remain in Java in Jhandles? Will they just be two
> similar OpenGL backends using different toolkits?

Anything that is not OpenGL rendering will be different, but
otherwise, they will be pretty similar (which is maybe a good thing...)

Michael.