Quote:Dolphin Developer
phire
25 points
·
3 years ago
So... AntiAliasing on the Gamecube...

As /u/JMC4789 mentioned, the Gamecube does have a 3x MSAA mode, basically nothing uses it, because the disadvantages are too large (the framebuffer is now 640x264, so you have to render the frame in two halfs to get a full 640x480 image).

Back in the dark ages before it was feasible to do SSAA and MSAA, game developers achieved 'AntiAliasing' through a simple post-processing blur effect.

GameCube developers relied on a few natural and unnatural sources of blur for this "AntiAliasing".

The Deflicker filter: A 3 line configurable vertical blur during EFB to XFB copy.
During the copy, it mixes the values for each pixel with the pixel above it and the pixel below it. Melee actually has a menu option to enable and disable this feature.

Color Subsampling: A 3 pixel horizontal blur during EFB to XFB copy.
After converting from RGB to YUV it mixes the color channels (U and V) with the color channels from the pixels to each side (hard-coded to 25% left, 50% center, 25% right). It then subsamples by 50% (tosses away every second U or V pixel).
This only applies to the color channels, the Luma channel (black and white) is untouched at this stage. But when your TV converts from YUV back to RGB, you will get some amount of blur.

Scanout resampling: A linear resampling during digital to analog conversion, aka more horizontal blur.
Most games render a 640px or 604px wide framebuffer. But the digital to analog pixel outputs 710 pixels per line. Most games add some kind of black bars, but unless the game has massive black bars (See Melee) there will still be some resampling, which slightly mixes pixel colors together, causing more horizontal blur.

The Composite cable: Analog filtering, resulting in more horizontal blur.
Rapid changes in the luma (black and white) channel will cause color artifacts to appear, so there are special filters to smooth these out, which you guessed it, results in more horizontal blur. And same thing on the color channels, those have even less bandwidth. Using component cables should eliminate this blur.

Your TV: Old CRT TVs are actually quite blurry, both horizontally and vertically.
And even your modern LCD will use a bilinear filter for upscaling, which is technically more blur.

I've been meaning to calculate exactly what this blur looks like, but you can probably get a very similar effect just by applying a gaussian blur to a screenshot from dolphin. If you work out a good set of blur settings, I'll be happy to add an equivalent post-processing shader to dolphin.

(09-04-2020, 08:51 PM)JosJuice Wrote: The deflicker filter can be disabled by turning on Graphics > Hacks > Disable Copy Filter. (The Android GUI acts as if this setting is off if you haven't yet set it, but it's actually on by default despite what the GUI tells you. I should fix that at some point...)

The conversion from RGB to YUV is only done if you disable Graphics > Hacks > Store XFB Copies to Texture Only, which is a very slow setting to disable for other reasons anyway.

The other sources of blur mentioned in phire's post are not emulated in Dolphin.