Re: circular_buffer?

From: boost_at_[hidden]
Date: 2001-02-27 13:49:28

Actually, neither of these is what I'm looking for.

Basically, (as a hobby) I am writing yet another shoot-em-up game. The
tried and true technique for managing bullets, ship thrust, bullet 
holes etc.  is to have a "ring buffer" or
"circular buffer" with a fixed maximum size.

You want a maximum of, say, 1000 bullets on the screen. As soon as the
ship fires the 1001st bullet, the 1st bullet "disappears". In terms 
of the buffer, asssuming it has a fixed size of "1000". When you add 
the 1001st entry, it overwrites the 1st entry.

The advantages are twofold:
1. You want to limit the number of artifacts anyway - having more 
than 1000 bullets, for example, would slow down the frame rate
2. It is efficient because it never needs to allocate memory.

It's pretty easy to do - but I was hoping for an "STL-friendly" 
version so that I can write

std::for_each(bullets.begin(), bullets.end(), draw_bullet);
std::for_each(bullets.begin(), bullets.end(), animate_bullet);

etc.

and

void ship::fire_bullet()
{
   g_bullets.push_back(bullet(initial_bullet_velocity_));
}

the idea being that g_bullets.capacity() would never increase unless 
you explicitly called reserve().

So in the above example, I would want the push_back call to just 
silently overwrite the oldest bullet, if the buffer was full.

Of course, a ring buffer like this is also useful for many network 
protocols that keep "sliding windows" of messages that might need to 
be resent etc. Most protocols define a "maximum" size of such a 
window - again, any error would occur only if you couldn't find an 
entry in the buffer at a later point, not when you are inserting a 
new entry (and thus possibly overwriting the oldest entry).

These are the type of problem domains a ring_buffer or 
circular_buffer would be used in.

Paul Hollingsworth
http://PaulHollingsworth.com

--- In boost_at_y..., Howard Hinnant <hinnant_at_t...> wrote:
> There were two ideas floating around:
> 
> 1.  A circular_buffer that would extend its capacity when necessary 
> (similar to vector and deque).
> 
> 2.  A circular_buffer that would throw an exception if the capacity 
was 
> exceeded.
> 
> Which one (or both?) are you interested in?
> 
> Personally I'm only interested in #1, and am willing to donate the 
> interface to an existing implementatation (taken pretty much from 
vector 
> and deque).  Unfortunately I can not donate the implementation 
itself, 
> but I would be happy to participate in and discuss design decisions 
on 
> such an implementation.
> 
> -Howard
> 
> boost_at_P... wrote on 2/24/01 6:30 PM
> >Hi everyone,
> >A while back there was a thread talking about a circular_buffer 
> >class. Does anyone know what happened?
> >
> >It would find it to be very useful.