Screen Space Ambient Occlusion (SSAO): Difference between revisions

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{{Note|'''This is a feature of Nvidia's drivers and not of the Source Engine. If you want to use this effect in your mod, you need to make your own shader.'''}}
{{stub}}
{{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.]]


[[{{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.]]
{{note | Not to be confused with baked ambient occlusion on models!}}


'''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.
{{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.


{{Note|Enabling ambient occlusion can cause significant performance penalties.}}
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.


This method of driver forced SSAO causes several rendering bugs in the Source Engine. Most notably, the SSAO shader does not take fog into account in it's AO calculations, producing visual artifacts in scenes with heavy fog.
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.]]


==Supported games==
==Source Filmmaker==
All [[Source]] engine games except [[Portal]] support Nvidia's ambient occlusion. Support in Portal can be forced on by editing Portal's profile in the Nvidia divers.
[[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 Nvidia's Ambient Occlusion==
 
[[{{ns:6}}:EnableAO.png|thumb|right|300px|Enabling AO in Nvidia control panel]]
== SSAO in the Source Engine ==
Ambient occlusion cannot be controlled through the video options within a Source game. AO is controlled by Nvidia's video drivers in the 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.
* 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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