what is XFB

[jonnyboyC]

More just a question of curiosity but what exactly does XFB do, i've always seen it in the config but never really knew what it did or why it was there, so pretty much what is it?

[neobrain]

Have fun reading:

<neobrain> NaturalVi: XFBs are just some chunks of RAM which are usually sth like 640x576 in size (for both PAL and NTSC and whatever else)
<neobrain> usually games only use one or two of them, they're used for moving stuff to the screen then: Game renders stuff to the EFB, copies it to the XFB, moves it to screen
<neobrain> when copying from EFB to XFB vertical stretching (plus filtering) can be applied. When moving stuff from XFB to screen, horizontal stretching is applied.
<shuffle2> VI technically supports other things too. gamma and horizontal stretching, plus other stuff
<neobrain> shuffle2: yeah, just that we want to keep it simple for NaturalVi for now xD
<shuffle2> lol
<neobrain> fwiw, the EFB uses other pixel formats than XFBs...the EFB uses RGB formats, whereas the XFB is YUV (or whatever it's called)
<neobrain> and XFBs obviously can directly be modified via the CPU additionally.. if one feels like doing that

<neobrain> now to Dolphin's implementation:
<neobrain> "virtual XFB" uses VRAM textures to emulate the XFB stuff as far as possible (doing a limited amount of the fancy stuff shuffle2 already mentioned, too), i.e. rather than displaying the EFB directly to the screen, it's first copied to another texture which then is displayed to the screen
<neobrain> (there can be multiple XFBs/textures involved in that process, but whatever..)
<neobrain> in contrast, when using real XFBs the EFB gets encoded to YUV(whatever) to the RAM (similiarly to "EFB to RAM") and when the VI is requested to display the XFBs' contents to the screen we decode it again to a texture which is then displayed

<n00b421> BTW what games do need xfb's?
<n00b421> never used this option....
<shuffle2> mostly homebrew because they sometimes write directly to xfb
<shuffle2> sometimes other games use it for effects or to display two halves of an AA'd image

One thing to add here: Obviously Dolphin's emulation of XFBs fails to track any CPU modifications if Virtual XFB is enabled.

[ExtremeDude2]

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