[racket] question on OpenGL support

From: Stephan Houben (stephanh at planet.nl)
Date: Mon Apr 11 15:32:00 EDT 2011

Hi list,

On 04/09/2011 05:51 AM, Jay Kominek wrote:
> The OpenGL APIs, all the versions, all the
> extensions, are described in some fairly parseable files available
> fromhttp://www.opengl.org/registry/  - look for the .spec files
> towards the bottom. I'm pretty sure you should be able to generate the
> bindings from those files, and more easily than dealing with C
> headers.

I wrote a bit of code to parse these files and it works fine so far.
I would like some advice though on how to wrap arrays in "output" mode.

Take for example the following function:

GetTexLevelParameteriv(target, level, pname, params)
	return		void
	param		target		TextureTarget in value
	param		level		CheckedInt32 in value
	param		pname		GetTextureParameter in value
	param		params		Int32 out array [COMPSIZE(pname)]

This corresponds to the C header:

    void glGetTexLevelParameteriv( GLenum target,
                                       GLint level,
                                       GLenum pname,
                                       GLint *params )

This function fills array "params" with some data.
The length of params depends on pname and is not directly specified.

I now wrap this as follows:

(_fun (target : _int32) (level : _int32) (pname : _int32) (params : _pointer) -> _void)

So params is just a raw pointer. I should perhaps use _i32vector in "output" mode instead but:
1. I don't have an expression for the length, and
2. I don't want to have the wrapper allocate and return an array; rather I want to mirror
    the C api exactly and pass in an array which is filled by the function.

The latter I consider especially important, since it ensures that all the docs for the C API can be used directly.

So what I really want is that a _i32vector is passed in for parameter "params", and then filled
by the function, so that the Racket program can observe the mutated vector.
Can this be achieved?



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