Path: chuka.playstation.co.uk!scea!greg_labrec@interactive.sony.com
From: Elliott Lee <tenchi@netmagic.net>
Newsgroups: scea.yaroze.programming.2d_graphics
Subject: Re: Big Sprite ?
Date: Tue, 10 Mar 1998 14:41:39 -0800
Organization: Cisco Systems
Lines: 97
Message-ID: <3505C1A3.29CCEC4E@netmagic.net>
References: <35047742.522A@hotmail.com> <3504AF57.559F@concentric.net> <35050925.6C5B@hotmail.com>
Reply-To: tenchi@cisco.com
NNTP-Posting-Host: dhcp-e-39-245.cisco.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 4.03 [en] (Win95; U)

Well, there is one visual effect that you can take advantage of by
doing it this way:  you could use it to make the background "fly"
apart at the end of the game, or you could make it bounce together
in the beginning.

e.g. suppose you loaded the background into sprites BGLeft and BGRight
     each being 160x240, had an OT with 1<<14 levels, and were dealing
     with 320x240 res:

void BgBounce( void )
{
int	x_vel = 0;

// set sprites to be off the edge of the screen
BGLeft.x  = -160;
BGRight.x = 160-BGLeft.x;
BGLeft.y  = 0;
BGRight.y = 0;

while( x_vel!=0 && BGLeft.x!=0 )
  {
  // do the buffer switch and clear the ordering table
  // (you may do it differently)
  activeBuff = GsGetActiveBuff();
  GsSetWorkBase((PACKET *)GpuPacketArea[activeBuff]);
  GsClearOt(0,0,&WorldOT[activeBuff]);

  // accellerate the graphic towards 0.
  if( BGLeft.x<0 )
    x_vel++;

  // add the velocity to current position
  BGLeft.x += x_vel;

  // make sure we don't pass 0!
  if( BGLeft.x>0 )
    {
    // reverse thrust!  also minimize the effect by about 2/3
    x_vel= 0-((x_vel*2)/3);

    // reset the "ground" level
    BGLeft.x = 0;
    }  // if( BGLeft.x>0 )

  // mirror the effect to the right sprite
  BGRight.x = 160-BGLeft.x;

  // paint the sprites into the background
  GsSortFastSprite( &BGLeft,&WorldOrderTable[activeBuff],1<<14 );
  GsSortFastSprite( &BGRight,&WorldOrderTable[activeBuff],1<<14 );

  //
  // *** insert other drawing stuff here... ***
  //

  // draw to buffer
  DrawSync(0);
  VSync(0);
  GsSwapDispBuff();
  GsSortClear(0,0,0,&WorldOrderTable[activeBuff]);
  GsDrawOt(&WorldOrderTable[activeBuff]);
  }  // while( x_vel!=0 && BGLeft.x!=0 )
}

I dunno if the above works---I haven't tested it---but I use something
similar in my current project.  ^_^

- e!
  tenchi@netmagic.net
  http://www.netmagic.net/~tenchi/yaroze/

Alex wrote:
> 
> Scott Cartier wrote:
> >
> > Alex,
> >
> > The maximum size for a sprite is 256x256 so you'll need to break it
> > up into two sprites.
> >
> > Scott
> 
> But there is no other way to have a BIG image in background?!
> I *MUST* set up a Sprite ? :( uh!
> 
> >
> > > Now another prob.. ;(
> > >
> > > In my game i must set a big picture in the background (320*240)!
> > >
> > > I defined this as a Sprite set to position 0,0!
> > > But at the edges the image was screwed up :(
> > >
> > > is there an other way to put this BIG picture in the background else
> > > than to define it as a Sprite ?!
> > >
> > > Alex.