Anti-aliasing has an intimidating name, but what it does for our computer displays is rather fundamental. Think of it this way -- a line has infinite resolution, but our digital displays vì chưng not.
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So when we "snap" a line to lớn the pixel grid on our display, we can compensate by imagineering partial pixels along the line, pretending we have a much higher resolution display than we actually do. Like so:
As you can see on these little squiggly black lines I drew, anti-aliasing produces a superior image by using grey pixels khổng lồ simulate partial pixels along the edges of the line. It is a hack, but as hacks go, it"s pretty darn effective. Of course, the proper solution to lớn this problem is to have extremely high resolution displays in the first place. But other than tiny handheld devices, I wouldn"t hold your breath for that khổng lồ happen any time soon.
This also applies to lớn much more complex 3d graphics scenes. Perhaps even more so, since adding motion amplifies the aliasing effects of all those crawling lines that hóa trang the edges of the scene.
But anti-aliasing, particularly at 30 or 60 frames per second in a complex state of the art game, with millions of polygons & effects active, is not cheap. Per my answer here, you can generally expect a performance cost of at least 25% for proper 4X anti-aliasing. And that is for the most optimized version of anti-aliasing we"ve been able lớn come up with:Super-Sampled Anti-Aliasing (SSAA). The oldest trick in the book - I danh mục it as universal because you can use it pretty much anywhere: forward or deferred rendering, it also anti-aliases alpha cutouts, and it gives you better texture sampling at high anisotropy too. Basically, you render the image at a higher resolution & down-sample with a filter when done. Sharp edges become anti-aliased as they are down-sized. Of course, there"s a reason why people don"t use SSAA: it costs a fortune. Whatever your fill rate bill, it"s 4x for even minimal SSAA.
Multi-Sampled Anti-Aliasing (MSAA). This is what you typically have in hardware on a modern graphics card. The graphics thẻ renders to a surface that is larger than the final image, but in shading each "cluster" of samples (that will over up in a single pixel on the final screen) the px shader is run only once. We save a ton of fill rate, but we still burn memory bandwidth. This technique does not anti-alias any effects coming out of the shader, because the shader runs at 1x, so alpha cutouts are jagged. This is the most common way to lớn run a forward-rendering game. MSAA does not work for a deferred renderer because lighting decisions are made after the MSAA is "resolved" (down-sized) lớn its final image size.
Coverage Sample Anti-Aliasing (CSAA). A further optimization on MSAA from NVidia
Pretty much all "modern" anti-aliasing is some variant of the MSAA hack, and even that costs a quarter of your framerate. That"s prohibitively expensive, unless you have so much performance you don"t even care, which will rarely be true for any recent game. While the crawling lines of aliasing vì chưng bother me, I don"t feel anti-aliasing alone is worth giving up a quarter of my framerate and/or turning down other details khổng lồ pay for it.But that was before I learned that there are some emerging alternatives khổng lồ MSAA. And then, much khổng lồ my surprise, these alternatives started showing up as actual graphics options in this season"s PC games -- Battlefield 3, Skyrim, Batman: Arkham City, & so on. What is this FXAA thing, & how does it work? Let"s see it in action:
| No AA4x MSAAFXAA |
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