Page flipping

[JoshG]

I understand how drawing to a back page and then making it the front page reduces flicker, but when you do that, do you change the video adress to the backpage, or do you copy the backpage to the front page? If you copied it, I don't see how it would make it faster. And would three pages be any smoother? I don't see how.

[lightatdawn]

>>do you change the video adress to the backpage, or do you copy the backpage to the front page?

You merely switch the 'front page' pointer to point to the 'back page'.

>>And would three pages be any smoother?

No. You cant get any faster than instant.

[JoshG]

Thank you, one more question, could you show me an example of using two pages, with pseudo code? This is how I figure it.

while(!quit)
{
  FlipPage();
  ParseInput(); // Which draws the stuff to the back buffer
}

I just don't understand how to set it up, I guess it would be different depending on the type of game, and the library used.

[mickey]

ere am not sure about this,


Draw on the backpage...
When the time comes to present your drawing....,
Point to the backpage,
Repeat

[JoshG]

Hmm, if you use two pages, I guess you would need a pointer to the back buffer too. How else would you know which one is the back buffer at the time...

[lightatdawn]

Yes, you will need a pointer to both the frint and back buffer. Otherwise you wouldnt be able to keep track of them.

A typical DirectX application using two pages would go something like this (pseodocode):

while(TRUE)
{
   //do stuff
   DrawImagesToBackBuffer();
   //do stuff
   Flip();
}

Flip() would merely make your back buffer your front (or 'main' buffer) and make your front buffer your back buffer. Then, on the next screen refresh, the contents of your ex-back buffer (the one you drew to last) would be displayed instead of your last front buffer (which is now the back one, all nice and ready to be drawn on for the next loop). Repeat.

(Hope that wasnt too confusing.)

[JoshG]

Not to confusing, I got it, thanks.

[mickey]

2 pointers??

isn't it just one pointer, and ddraw just points back and forth between these two buffers,

[jdinger]

Originally posted by mickey
isn't it just one pointer, and ddraw just points back and forth between these two buffers,

Nope. Where do you think it keeps the info about the 2 buffers? At the addresses of their respective pointers.

//long pointer to an IDirectDrawSurface object for the primary surf
LPDIRECTDRAWSURFACE7 sfPrimary=NULL; 
//long pointer to an IDirectDrawSurface object for the backbuffer
LPDIRECTDRAWSURFACE7 sfBackBuffer=NULL;

sfBack->BltFast(20,20,sfYourBmpSurf,&ItsRect,DDBLTFAST_WAIT);
sfPrimary->Flip(NULL,DDFLIP_WAIT);

Read the DirectX docs that come with the SDK.

from DX SDK documentation

HRESULT Flip(
LPDIRECTDRAWSURFACE7 lpDDSurfaceTargetOverride,
DWORD dwFlags
);

Parameters
lpDDSurfaceTargetOverride
Address of the IDirectDrawSurface7 interface for an arbitrary surface in the flipping chain. The default for this parameter is NULL, in which case DirectDraw cycles through the buffers in the order that they are attached to each other