[HOpenGL] Specialized versions of renderPrimitives?
sven.panne at aedion.de
Fri Oct 27 03:49:39 EDT 2006
Am Freitag, 27. Oktober 2006 00:04 schrieb Bas van Dijk:
> On Thursday 26 October 2006 18:39, Henning Thielemann wrote:
> > It would be more concise and safer to write
> > lineLoop [v1, v2, v3, v4]
> > lines [(v1, v2), (v3, v4)]
> If I understand the following correctly:
> With renderPrimitive you can also add additional properties per vertex.
> Like: [...]
Yes, exactly. In
you can see all the attributes a vertex has when using the traditional fixed
function pipeline. When using GLSL (not yet implemented in my binding), a
vertex can have an arbitrary number of additional attributes.
> It would be possible to do it in a type safe manner by having a data type
> Vertex that has a list of VertexProperties:
> type Vertex = [VertexProperty]
> data VertexProperty = Coordinate ...
> | Color ...
> | TextureCoordinate ...
This doesn't cover arbitrary attributes used by GLSL, but of course we could
have a few more alternatives in VertexProperty for this. And of course you
would need different alternatives for e.g. Color3, Color4,
TextureCoordinate1, etc. What makes this a little bit ugly is the fact that
one would have to use different constructors for places in the API where e.g.
exactly a color value with 4 floating point components is expected. A
VertexProperty would be much too general in those cases, therefore I've
chosen to use type classes.
One thing I don't fully understand: What is not type safe in the current API?
The only thing I see is that one could use a different monad within
renderPrimitive to enforce that only correct OpenGL command could be issued
there. But having direct access to the IO monad is more important to access
e.g. IORefs etc. within the action passed to renderPrimitive than a
marginally safer typing. There are tons of places in OpenGL where the caller
can do something wrong which can't be detected by type inference.
And a final hint: No serious OpenGL program will make heavy use of
renderPrimitive, vertex arrays and/or buffer objects are the way to go for
larger sets of data:
The renderPrimitive way of throwing data at the OpenGL pipeline is not even
included in OpenGL ES, and it is on the death row for future versions of the
full OpenGL, too.
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