Anti-aliasing

Comparison of no anti-aliasing and 8x MSAA. Click to enlarge

Anti-aliasing (AA) is a graphics technique extensively employed in Valve video games, such as those in the Half-Life series, as well as in other software applications developed by Valve, including Steam and Source Filmmaker, etc. This technique is utilized to enhance the visual quality and reduce the jagged edges, or jaggies, that can appear in computer-generated imagery.

Computer monitors are essentially a large grid of squares that can be set to any color or brightness. As such, it is impossible to draw a perfectly straight line, because no matter how many squares there are, it will never be able to make a perfectly smooth diagonal. This creates a stair-step pattern that gets increasingly noticeable the lower the resolution is, which is often referred to in the video game world as "Aliasing". Spatial anti-aliasing, often referred to simply as anti-aliasing, is designed to combat the problems of aliasing. In simple terms, anti-aliasing is designed to smooth out that stair-step pattern in images and make them look less pixelated, while not changing the resolution of the final image.

While anti-aliasing is available on PC, it was often not supported on consoles until the release of Portal 2 (which uses MLAA on PlayStation 3), as traditional methods like MSAA are very expensive, compared to post-processing methods like FXAA/TAA/MLAA used in later games. In all Source 2007 games and above on Xbox 360, it uses software AA, which is not as effective as newer post-processing methods.

Overview

Traditional methods

SSAA

SuperSampling Anti-Aliasing, also known as Full Scene Anti-Aliasing (FSAA) in some games and often interchangeable with the term downscaling.

Technically when implemented correctly, these do differ in that downscaling applies to an entire frame buffer – 2D and 3D Elements, while SSAA/MSAA are techniques only applied internally to 3D elements. In some implementations this can result in a lesser performance impact and better compatibility.

Compared to MSAA, SSAA/FSAA produces the same result as MSAA, but completely reduced stair-step pattern in alpha textures. Additionally, ReShade depth buffer detection works with SSAA. However, SSAA is very expensive when it comes to performance compared to MSAA, and SSAA is not available as an option in Source by default, but can be enabled below:

On NVIDIA graphics cards, it's implemented as OGSSAA (Ordered Grid Supersample Anti-Aliasing), and can only be enabled through third-party applications such as Nvidia Profile Inspector, using the following modes: 2x1, 1x2, 2x2, 3x3, 4x4. OGSSAA also only supports Direct3D.

Important:If you are building cubemaps, enabling SSAA (or OGSSAA/downscaling) will cause cubemaps (especially HDR cubemaps) to be built very slowly (even on powerful GPUs). Make sure SSAA (or OGSSAA) is disabled before building cubemaps. Other AA methods such as MSAA are not affected by this.

Downscaling

Downscaling or downsampling is a brute-force method for AA, which applies SSAA to both 2D (such as HUD and UI) and 3D elements by running the game at a higher resolution. It can be enabled on graphics card control panel as NVIDIA DSR or AMD VSR. Unlike SSAA, downscaling will produce blurrier results and does not get rid of the shimmering effect on transparent textures/objects.

Another downside to downscaling is that many older games' UI (such as VGUI used in Half-Life 2) will become smaller at higher resolutions.

MSAA

MultiSample Anti-Aliasing (MSAA) was the gaming industry standard of anti-aliasing (prior to the TAA gradually replacing MSAA in mid-late 2010s as games transitioned from forward rendering to deferred rendering), and as such is the only version available (alongside CSAA on NVIDIA cards prior to Maxwell) in all Source games before Counter-Strike: Global Offensive, and later available in GoldSrc in 2013, with only MSAA 4x being available, which is enabled by default. In GoldSrc, the anti-aliasing can be disabled by starting with the -nomsaa launch option. Essentially, if a polygon is crossing a multisample point, or subpixel, it detects how many of its neighboring points are also being intersected, then takes the color of that polygon and adds it over the existing image to create a slightly smother line. This creates a smoother line, but does not completely remove the stair-step pattern (especially on alpha textures that don't use alpha to coverage) without combining FXAA/SMAA/other post-FX AA methods with MSAA, plus games that use deferred rendering and MSAA may not work properly and can cause various other issues. This is usually sufficient for most users, however.

All GoldSrc, Source and Source 2 games contain 3 different settings of MSAA, which include:

2x
4x - Default level in post-SteamPipe GoldSrc (can be enhanced in GPU control panels)
8x - Very expensive on older/low-end hardware. Introduced in Source 2006. You can enable 8x MSAA in Source 2004 by using the mat_antialias 8 console command, or force it through driver settings.^[1]

What this does is add more subpixels to a specified location and increases the accuracy of the multisampling, at the cost of performance. Some alternative anti-aliasing methods such as the post-processing one will be less demanding compared to MSAA or other methods.

Warning:If MSAA is enabled, ReShade depth buffer detection will stop working, which means that you are unable to use some AA methods, for example (such as some versions of TAA), or even shaders such as SSAO in general.

Note:Previous version of engine branch,

Source 2004, has an option for MSAA 6x. This setting of MSAA does not work on modern graphics cards or newer drivers, and was replaced by MSAA 8x.

Note:alpha to coverage requires MSAA, as it is a multisampling method. Alternatively, SSAA can be used instead to reduce jagged edges on alpha textures and objects.

CSAA^{[ Deprecated]}

Coverage Sampling Anti-Aliasing (CSAA) was an NVIDIA-exclusive method of anti-aliasing, introduced with the GeForce 8000 Series. It aims to further reduce the additional stress that MSAA puts on the system, with NVIDIA claiming that a CSAA-rendered image will rival 8x-16x MSAA while only putting a load on the system comparable to 4x MSAA. It does this by reducing the number of settings each sample determines (by creating a new sample for coverage) while increasing the overall number of samples.

However, by the release of Maxwell-based GPUs such as GTX 750 Ti, GTX 800M/900 series in 2014, and newer NVIDIA graphics card (or drivers released around Feb 2014 onwards which affects GeForce 400 series card and above) drops support for CSAA completely, and MFAA completely succeeded it, with lots of limitations however.

Source natively support CSAA since Source 2007. Support for CSAA was broken on some newer NVIDIA GPUs starting with GeForce 400 series (or Maxwell and newer NVIDIA cards) with new driver update, or Source 2013 update.^[2]

Post-processing methods

Software AA

(in all games since ) All Source engine games since Source 2007 introduced software AA, which blurs the jagged edges (similar to FXAA or other post-processing AA). It currently only works on Source 2007 games (tested on Black Mesa 2012/mod version). Software AA is also supported (and used) in Xbox 360 port of Source engine games.

Bug:Software AA is currently broken in all Source 2013 games. It is also broken (or non-functional) in Left 4 Dead engine branch^[3] and above. (tested in:

,

, Source SDK Base 2013.)

FXAA

Fast Approximate Anti-Aliasing (FXAA) is a post-processing anti-aliasing with a low performance cost. The main advantage of this technique over regular anti-aliasing is that it doesn't require a lot of computing power, and is also capable of smoothing out alpha-blended textures (aka transparent textures). Its main drawback is that it blurs the final image, so textures will look less sharp, and plus, they don't recover the missing pixel (or alpha to coverage) without using FXAA with MSAA simultaneously (or by downscaling). Regular Source (prior to CS:GO engine branch, or in third-party engine branch such as Xengine) doesn't have support for it but as FXAA is a post-processing effect, it can easily be implemented like with the Source shader editor or with ReShade.

Important:Using ReShade for multiplayer games and connecting to a VAC-secured server is not recommended.
Additionally, using ReShade on Counter-Strike: Global Offensive and Counter-Strike 2 requires the -allow_third_party_software and -insecure command-line options, which would prevent you from connecting to any VAC-secured server.

MLAA

Morphological Anti-Aliasing (MLAA) is a post-processing anti-aliasing typically available on AMD cards, but it can be used with any other graphics card. It's similar to NVIDIA's FXAA but has a higher performance cost, but is less demanding compared to MSAA. It's used in PlayStation 3 version of Portal 2.

Confirm:What about

Counter-Strike: Global Offensive on PS3?

SMAA

Subpixel Morphological Anti-Aliasing (SMAA) works similarly to FXAA or MLAA (which is what SMAA was based off), but results in much better image quality than both FXAA and MLAA, while also taking little performance impact. There are currently no GoldSrc, Source or Source 2 games using this AA method, but users can add SMAA by using ReShade or Source Shader Editor.

Temporal methods

TAA/TSSAA

Temporal Anti Aliasing (TAA) is an anti-aliasing technique that reduces shimmering or flickering effects by smoothing the frame when in motion. There are multiple implementations of TAA, but the most common one is TSSAA (Temporal Super-Sampling Anti-Aliasing) which combines information from past frames (usally 8 frames) and the current frame, while also slightly jittering to smooth the current frame. Each pixel is sampled once per frame but in each frame the sample is at a different location within the pixel. Pixels sampled in past frames are blended with pixels sampled in the current frame to produce an anti-aliased image. While being cheaper to calculate than MSAA, and produces image similar to super sampling anti-aliasing (SSAA) or downscaling, its main drawback is that it can cause ghosting and blurriness to the image, especially when in motion, noticeable with lower framerate or resolution, depending on the implementation (Example here). Some of the drawbacks can be mitigated by adding a sharpening filter.

As of mid 2010s, it's the current gaming industry standard of anti-aliasing (alongside FXAA for weaker hardware) with many modern games (except many VR and mobile games) started to use TAA as most modern games transitioned from forward rendering to deferred rendering, which allows many lights to be rendered without a significant performance hit.

Apex Legends as well as Titanfall 2 are the only Source games that uses TSSAA, while Titanfall uses TXAA which requires MSAA to function. Portal with RTX and all other RTX Remix games also use TSSAA anti-aliasing, through DLSS (or DLAA). One upcoming Source 2 game made by Valve, Deadlock, supports TAA through AMD FSR2. Both DLSS, XeSS and FSR 2.0 (and later) not only apply TAA anti-aliasing (using AI/Tensor Cores), but also improve performance by rendering the image at lower resolutions then scaling to higher resolutions.

TXAA

TXAA is an older form of TAA that creates a smoother, clearer image than any other anti-aliasing solution by combining MSAA with Nvidia-designed temporal filters. TXAA can result in much sharper image quality compared to TAA, depending on the implementation in some games. TXAA is supported with Nvidia GeForce GTX 600 series or higher, and requires MSAA to be enabled in order to use.

CMAA

Conservative Morphological Anti- Aliasing (CMAA) is an image-based post-processing technique originally developed by Filip Strugar at Intel. CMAA uses 4 main steps to reduce aliasing:

Color break detection
Locally dominant edge detection
Simple shape handling
Symmetrical long edge shape handling.

CMAA, while having slight performance impact compared to FXAA, but still has less performance impact than SMAA, CMAA manages high quality anti-aliasing while preserving text and without over blurring the geometry.

CMAA is currently only implemented in Counter-Strike 2.

Note:When

Counter-Strike: Global Offensive got ported to

Source 2 (and renamed to

Counter-Strike 2), (FXAA) support was removed and (CMAA) was implemented in its place, with the ability to use it alongside MSAA removed.

Media

Tip:Click on one of the images below, after it's fully loaded, click on it again to view it in full resolution.

GoldSrc

FXAA (through ReShade)

SMAA (through ReShade)

4x MSAA (default)

No MSAA

Source

No anti-aliasing

2x MSAA

4x MSAA

8x MSAA

FXAA through the Source shader editor