Passing dynamic arrays into C.

[Daniel Murphy]

It should work if you treat the dynamic array like a pointer and a length.
eg:
glBufferData(GL_ARRAY_BUFFER, (vertices[0]).sizeof * vertices.length,
                   vertices.ptr, GL_STATIC_DRAW);

It's probably because (type).sizeof gives the number of bytes to hold the 
type.
For dynamic arrays, this is the size of the (length, pointer) pair and not 
the array itself.

float.sizeof // gives 4
int.sizeof // gives 4
int[].sizeof // gives 8
int[3].sizeof // gives 12

class C { int[100] d; };
C.sizeof // gives the size of the reference, not the instance.

I haven't checked the sizes, but it generally follows something like that.


"Bernard Helyer" <b.helyer at gmail.com> wrote in message 
news:hr0veq$2269$1 at digitalmars.com...
>I was having a problem interfacing with OpenGL from D, as demonstrated by 
>this program, written once in D, and again in C:
>
> http://gist.github.com/378273
>
> Now the 'gist' of it is, doing things like this (D):
>
>     glBufferData(GL_ARRAY_BUFFER, vertices.sizeof,
>                  vertices.ptr, GL_STATIC_DRAW);
>
>     glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);
>
> With this data (D):
>
>     const GLfloat[] vertices = [-1.0f, -1.0f, 1.0f, -
>                                  1.0f, -1.0f, 1.0f, 1.0f, 1.0f];
>
> and the same data in C:
>
>     const GLfloat vertices[] = {-1.0f, -1.0f, 1.0f,
>                                 -1.0f, -1.0f, 1.0f, 1.0f, 1.0f};
>
>
> I was getting nothing but a blank screen. I'm sure you smart folks know 
> what comes next.
>
>      GLfloat[] vertices = {1.0f, 1.0f};  // vertices is a dynamic array.
>
>      GLfloat[2] vertices = {1.0f, 1.0f};  // vertices is a static array.
>
> The second version enables the program to work as the C one does.
>
>
> My question is, why doesn't passing the `GLfloat[] vertex ...` declaration 
> work? I've looked through the docs, and can't see anything too obvious.
>
>
> Thanks.