Screen Space Ambient Occlusion (SSAO): Difference between revisions

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[[{{ns:6}}:Prop ragdoll.jpg|thumb|400px|SSAO in game - the shading effect is highly visible between Breen and the table, but also appears in the corners of the room. Note the edge "glow" bug around Breen's arm.]]
{{Todo|Document about HBAO, alternative to SSAO which can be forced through GPU driver control panel (or NVIDIA Profile Inspector).}}
[[File:AmbientOcclusionExample.jpg|right|210px|thumb|An example of traditional ''prerendered'' ambient occlusion in Blender 3D. SSAO attempts to mimic this look in real-time.]]


'''Ambient Occlusion (AO)''' is a type of [[lighting]] technique applied in-game to create more realistic lighting. AO simulates soft shadows created by two surfaces that are close together. Ambient occlusion in games is normally accomplished through '''[[Wikipedia:Screen Space Ambient Occlusion|Screen Space Ambient Occlusion]]''', which is a simplified way to fake realistic AO with shaders in a process fast enough for real-time rendering. SSAO is a [[DirectX]] 9.0c shader, so it will only be available on fairly modern video cards.
{{note | Not to be confused with baked ambient occlusion on models!}}


The [[Source]] engine does not directly support ambient occlusion, so it is not found in Source's video options; it currently can only be enabled for nVidia graphics cards via the nVidia drivers.
{{TODO|Expand the article to include different methods of SSAO. The method described is one of many.}}<br>


SSAO works by examining an onscreen pixel, and then comparing its location in the depth buffer (i.e. how far it is away from the player) to the pixels around it. Pixels which are close together but not coplanar (on the same face) are shaded to simulate soft shadows. To maintain playable framerates, it is not possible to sample every pixel every frame, so random sampling is used, which will inevitably create noise/grain which may be more noticable when the player moves around.
'''Screen Space Ambient Occlusion''' ('''SSAO''') works by examining an onscreen pixel, and then comparing its location in a [[depth buffer]] to the pixels around it. Pixels which are close together but not coplanar (on the same face) are shaded to simulate soft shadows. To maintain playable framerates, it is not possible to sample every pixel every frame, so random sampling is used, which will inevitably create noise/grain which may be more noticeable with movement. To counter this, the SSAO pass is often blurred to remove such grain.


Enabling ambient occlusion will generally cause a significant drop in performance, particularly on older cards - framerates may be reduced by more than half.
As with traditional AO, SSAO is completely independent of the normal lighting system. This means that both the performance and appearance of the shader are unaffected by the lights used in a level.


SSAO causes several rendering bugs which are common to nearly all games which offer SSAO.
The depth buffer is measured from the camera, and so SSAO is view-dependent - the size and locations of the "shadows" created by SSAO may change as the player moves the camera around. Additionally, the shading may look different along the edges of the screen - this can be combated by rendering additional information outside of the current camera's bounds.
[[{{ns:6}}:Ao_renderbug_trees.jpg|thumb|right|300px|The shadows being rendered on top of fog are noticable on distant trees.]]
{{bug|SSAO often creates a small visual error where the very edge of an object is not shaded, causing an apparent glow.}}
{{bug|SSAO is rendered ''on top of fog and smoke'', even if the smoke is closer to the player than the source of the shading, causing the fog/smoke to look lumpy. This may give distant trees a frosted look, and in some cases allows the player to discern objects that would normally be completely obscured by fog.}}


==Supported games==
==Source Filmmaker==
All [[Source]] engine games except [[Portal]] support nVidia's ambient occlusion. This may be because AO would not render correctly through Portals.
[[Source Filmmaker]] includes an SSAO option (labelled "Ambient Occlusion"), accessible by right-clicking on the viewport. The default setting is very grainy. {{todo|Adjust number of samples?}}


==Enabling ambient occlusion==
== SSAO in the Source Engine ==
[[{{ns:6}}:EnableAO.png|thumb|right|300px|Enabling AO in nVidia control panel]]
* The original release of {{dota2|4}} aswell as {{sfm|1}}, and all games on {{titanfall|4}} branch are the only {{src|4}} games and software that support SSAO.
Ambient occlusion cannot be controlled through the video options within a Source game. AO is controlled by video drivers. For NVidia users, this is found in the NVidia Control Panel. ATI Catalyst Control Center does not currently offer a driver-based AO option.
* However, as SSAO is a post-processing effect, you can use third-party software (ReShade), or [[Source Shader Editor]] to add SSAO. Alternatively, it is possible to use the superior HBAO ambient occlusion, which can be forced through GPU driver control panel (or by using NVIDIA Profile Inspector).
{{Note|For baked Ambient Occlusion maps per model within the Source Engine, see [[$ambientocclusion]].}}
{{Note|A post process SSAO shader currently ships with the [[Source_shader_editor| Source Shader Editor]].}}
{{TODO|Write a tutorial on creating an SSAO shader and implementing it into the engine. See [[Shader Authoring]].}}
{{Note|I am currently writing a tutorial on implementing SSAO into Source Engine [http://www.moddb.com/games/lost-squad/tutorials/source-engine-implementing-simple-ssao-shader-part-1 here] (DmitRex).}}
 
==External links==
*[[Wikipedia:Ambient occlusion]]
*[[Wikipedia:Screen Space Ambient Occlusion]]

Latest revision as of 21:47, 8 February 2025

Stub

This article or section is a stub. You can help by expanding it.

Todo: Document about HBAO, alternative to SSAO which can be forced through GPU driver control panel (or NVIDIA Profile Inspector).
An example of traditional prerendered ambient occlusion in Blender 3D. SSAO attempts to mimic this look in real-time.
Note.pngNote: Not to be confused with baked ambient occlusion on models!
Todo: Expand the article to include different methods of SSAO. The method described is one of many.


Screen Space Ambient Occlusion (SSAO) works by examining an onscreen pixel, and then comparing its location in a depth buffer to the pixels around it. Pixels which are close together but not coplanar (on the same face) are shaded to simulate soft shadows. To maintain playable framerates, it is not possible to sample every pixel every frame, so random sampling is used, which will inevitably create noise/grain which may be more noticeable with movement. To counter this, the SSAO pass is often blurred to remove such grain.

As with traditional AO, SSAO is completely independent of the normal lighting system. This means that both the performance and appearance of the shader are unaffected by the lights used in a level.

The depth buffer is measured from the camera, and so SSAO is view-dependent - the size and locations of the "shadows" created by SSAO may change as the player moves the camera around. Additionally, the shading may look different along the edges of the screen - this can be combated by rendering additional information outside of the current camera's bounds.

Source Filmmaker

Source Filmmaker includes an SSAO option (labelled "Ambient Occlusion"), accessible by right-clicking on the viewport. The default setting is very grainy.

Todo: Adjust number of samples?

SSAO in the Source Engine

  • The original release of Dota 2 Dota 2 aswell as Source Filmmaker, and all games on Titanfall Titanfall branch are the only Source Source games and software that support SSAO.
  • However, as SSAO is a post-processing effect, you can use third-party software (ReShade), or Source Shader Editor to add SSAO. Alternatively, it is possible to use the superior HBAO ambient occlusion, which can be forced through GPU driver control panel (or by using NVIDIA Profile Inspector).
Note.pngNote:For baked Ambient Occlusion maps per model within the Source Engine, see $ambientocclusion.
Note.pngNote:A post process SSAO shader currently ships with the Source Shader Editor.
Todo: Write a tutorial on creating an SSAO shader and implementing it into the engine. See Shader Authoring.
Note.pngNote:I am currently writing a tutorial on implementing SSAO into Source Engine here (DmitRex).

External links

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