Re: [AD] implementing seek

[Matthew Leverton <meffer@xxxxxxxxxx>]

On Wed, Apr 7, 2010 at 10:04 PM, Peter Wang <novalazy@xxxxxxxxxx> wrote:
> On 2010-04-07, Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx> wrote:
>> Probably like any handle would, except it gets EOF when/after it reaches the
>> end of the slice. so its impossible to overwrite past the end.
>
> I was wondering how the user would know how big to make the slice,
> ahead of time.
>
> Ok, if the al_fopen_slice 'length' parameter is a _maximum_ length,
> then you can pass INT_MAX or some other big number.  When the slice is
> closed we set the file position to initial_slice_pos + max_slice_length,
> or the end of the file, which comes first.
>
I haven't thought writing through yet... But my initial thought was
that the splice is always a well defined length.

I would think that writing should generally be sequential, and you
wouldn't need to set up a splice. i.e., Loaders would just happily
write the contents out start to end, never even trying to seek. As
such, you could pass the "real" file handle without any issues.

That said, I suppose it would be naive to assume that.

A large number is probably better than 0 for indicating arbitrary length.

One edge case to consider would be what SEEK_END should be on an open
ended splice ... you have the written length as well as the parent
file's length.

e.g.,

fp = al_fopen(); // file with 10 bytes
slice = al_fopen_slice(fp, INT_MAX);
al_fseek(slice, 0, ALLEGRO_SEEK_END);

Should that go to position 10, or stay at 0, since the slice hasn't
been written to?


--
Matthew Leverton