Difficulty copying multi dimensional static array to dynamic array.

[Spacen Jasset]

Derek Parnell wrote:
> On Tue, 26 Feb 2008 09:39:49 +1100, Derek Parnell wrote:
> 
>> On Mon, 25 Feb 2008 23:11:11 +0100, Saaa wrote:
>>
>>> Using ref should do the trick without pointers.
> 
> Oh and if it's "tricks" you want ;-) this works ...
> 
> import std.stdio;
> struct nastytrick(T)
> {
>     T m;
> }
> 
> alias float[3][5]       a2D;
> alias nastytrick!(a2D) sa2D;
> 
> void fillArray(ref sa2D data)
> {
>   invariant int maxi = data.m.length;
>   invariant int maxj = data.m[0].length;
>     
>   for (int i = 0; i < maxi; i++)
>       for (int j = 0; j < maxj; j++)
>         data.m[i][j] = i*maxj + j;
>   
> }
> void main()
> {
>     sa2D x; // declare static array inside its struct wrapper.
>     fillArray( x );
>     std.stdio.writefln("%s", x.m);
> }
> 
> It seems very odd that a struct can be passed using 'ref' but a fixed
> length array can't be. 
> 
I don't see the mystery. Arrays are *always* passed by reference. You 
can't use ref because can't change a ref to a static array (becuase it's 
static?) so it doesn't actually make sense, you can [I think] with a 
class object -- Chanage it's ref using "ref" keyword so that it points 
to a new object) So that is all fine and makes sense as far as I can see.

My beef is returning static arrays which you can't do. You can return 
dynamic ones only.

It makes this impossible:

glMatrixMultiply( mymatrix.toFloatArray16() );

Instead you have to do something like this:

float[4][4] temp;
mymatrix.toFloatArray16ByRef( temp );
glMatrixMultiply( temp );

Or

glMatrixMultiply( *temp.toFloatArrayPointer() );

toFloatArrayPointer is:

float[16] * toFloatArrayPointer()
{
	static float[16] matrix;
	return &matrix;
}


...and then you can use a wrapping structure and so on. But this isn't 
'right' is it? or is it? Can why can I not use something like:

glMatrixMultiply( mymatrix.toFloatArray16() );

where toFloatArray16 is:

float[4][4] toFloatArray()
{
	float[4][4]	a;
	return a; // a is returned like a struct would be. (i.e. copied onto 
the stack and copied off on return. (or usually optimsed via a pointer 
on the stack to the callers object perhaps - whatever dmd currently does)
}