Re: [AD] Fw: Acquire/Release speed issue

[Angelo Mottola <a.mottola@xxxxxxxxxx>]

> The Windows windowed driver also emulates page flipping, and it does 
> reuse
> the screen like the fullscreen one.
>
> > With emulation how I did it, you have the real "screen" BITMAP, and 
> > each
> > time you call create_video_bitmap(), it returns a new BITMAP. You 
> > draw into
> > one of these, then show_video_bitmap() copies onto "screen". If I 
> > reuse
> > the screen, this doesn't work, as with emulation "screen" is always
> > displayed, no matter if you call show_video_bitmap() to flip pages...
>
> The technique is to swap the underlying surfaces on each call to
> show_video_bitmap()

Here things are not that easy: there is no "surface" for the real 
screen. You can directly get the framebuffer pointer, and that's what 
is done to set up the screen BITMAP line pointers. So if I reuse it, 
it'll work like this:

Assume page1 is the reused screen, and page2 is another page.

                  Visible on display            Offscreen

before flip:      page1 == screen               page2
                  page1->line[0] = 0xA0000      page2->line[0] = 0xB0000

If on flipping I copy the contents of page2 on "screen", I display it. 
But line pointers are still the same, so on the next frame the user 
will be assuming that page2 is on screen, so page1 is offscreen so it 
is valid to write on it... while page1 line pointers still point to the 
real screen, thus whatever the program draws will instantly overwrite 
the just copied page2 on the displayed screen.

after flip:       page2                         page1 == screen
                  page2->line[0] = 0xB0000      page1->line[0] = 0xA0000

Here we're talking about a fullscreen mode where you have direct access 
to the screen... so tricks like the one you suggested won't work.
Or am I missing something?

--
Angelo Mottola
a.mottola@xxxxxxxxxx