SpecializedSource checked

Screen Space Ambient Occlusion

Approximates ambient occlusion from the visible depth buffer.

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Quick Facts

Compact metadata for implementation and discovery.

Category: Rendering
Difficulty: Intermediate
Family: Screen-Space Effect
Tier: Specialized
Status: Verified
Review: Source Checked
Sources: 1
Formulas: 1
Relationships: 3
Code example: Not ready
Visualization: Ready
Aliases: SSAO

Overview

SSAO samples nearby screen-space depths to estimate local occlusion without tracing the full scene.

Core Concepts

rendered imageocclusion samplingdeadline constraintscreen-space effectscene representationvisibility testpixel output

Quick facts

Complexity

Runtime and memory behavior at a glance.

Best

O(p s)

Average

O(p s)

Worst

O(p s)

Space

O(p)

When to Use

Use Screen Space Ambient Occlusion when you need to sample depth around each screen pixel.
Use it for real-time rendering with inputs like depth buffer.
Use it when the scene representation and quality target match the rendering tradeoff.
Use it when the Screen-Space Effect tradeoff is acceptable for the problem size.

When Not to Use

Avoid it when worst-case timing cannot be bounded well enough.
Avoid it when the cost per pixel or sample is too high for the desired frame rate.
Avoid it when the required output is not screen-space occlusion texture.

What It Does

Samples depth around each screen pixel
Estimates local blocked light from visible geometry

Use Cases

Real-time rendering
Game post-processing
Contact shadow approximation

Inputs

Depth buffer
Normal buffer
Sample kernel

Outputs

Screen-space occlusion texture

Key Formulas (1)

Screen-space occlusion

occlusion = blocked_samples / sample_count

occlusion = blocked_samples / sample_count

Approximates local occlusion from nearby depth-buffer samples.

Pseudocode

1.Read each pixel's depth and normal
2.Sample nearby positions in screen space
3.Compare sample depths
4.Accumulate occlusion
5.Blur and apply the result

Canonical Example

Input: scene = one triangle, one camera, one light
Output: image pixels showing the visible triangle
Explanation: Screen Space Ambient Occlusion: The algorithm converts scene data into visible pixel results.

Implementation Notes

Keep the input contract explicit: Depth buffer; Normal buffer; Sample kernel.
Use this step as the implementation spine: Read each pixel's depth and normal.
Then preserve the next state change: Sample nearby positions in screen space.
Build tiny scenes with known geometry before testing complex materials or lighting.

Common Pitfalls

SSAO cannot account for geometry that is not visible in the current frame.
Ignoring coordinate spaces, depth precision, or sampling noise while debugging image artifacts.
Returning screen-space occlusion texture without handling empty, invalid, or boundary inputs.

Interactive Mechanism Walkthrough

Spatial Primitive & Sweep-Line Canvas

Show a depth buffer producing dark contact regions.

Step 1 of 5: Read each pixel's depth and normal

screen-space-occlusion

Notes

Screen Space Ambient Occlusion operates in O(p s) time and O(p) space within the Screen-Space Effect family. Key governing relation: occlusion = blocked_samples / sample_count. Often compared with Ambient Occlusion and Shadow Mapping.