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Ambient Occlusion

Darkens areas where nearby geometry blocks ambient light.

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Quick Facts

Compact metadata for implementation and discovery.

Category: Rendering
Difficulty: Intermediate
Family: Lighting Approximation
Tier: Core
Status: Verified
Review: Source Checked
Sources: 1
Formulas: 1
Relationships: 3
Code example: Not ready
Visualization: Ready
Aliases: AO

Overview

Ambient Occlusion estimates how exposed each surface point is to surrounding light and darkens creases or contact areas.

Core Concepts

rendered imageocclusion samplinglight contributionlighting approximationscene 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 Ambient Occlusion when you need to sample nearby visibility.
Use it for contact shadows with inputs like surface points or depth buffer.
Use it when the scene representation and quality target match the rendering tradeoff.
Use it when the Lighting Approximation tradeoff is acceptable for the problem size.

When Not to Use

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 occlusion factor per point or pixel.

What It Does

Samples nearby visibility
Reduces light where geometry is enclosed

Use Cases

Contact shadows
Model previews
Realistic surface grounding

Inputs

Surface points or depth buffer
Sampling radius

Outputs

Occlusion factor per point or pixel

Key Formulas (1)

Occlusion estimate

occlusion = blocked_samples / total_samples

occlusion = blocked_samples / total_samples

Estimates how much nearby geometry blocks ambient light.

Pseudocode

1.For each surface point, sample nearby directions or positions
2.Check how many samples are blocked
3.Average the blocked fraction
4.Apply the occlusion factor to shading

Canonical Example

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

Implementation Notes

Keep the input contract explicit: Surface points or depth buffer; Sampling radius.
Use this step as the implementation spine: For each surface point, sample nearby directions or positions.
Then preserve the next state change: Check how many samples are blocked.
Build tiny scenes with known geometry before testing complex materials or lighting.

Common Pitfalls

Ambient Occlusion approximates indirect shadowing rather than full light transport.
Ignoring coordinate spaces, depth precision, or sampling noise while debugging image artifacts.
Handle empty, invalid, and boundary inputs before trusting occlusion factor per point or pixel.

Interactive Mechanism Walkthrough

Spatial Primitive & Sweep-Line Canvas

Show creases darkening as nearby samples become blocked.

Step 1 of 4: For each surface point, sample nearby directions or positions

occlusion-samples

Notes

Ambient Occlusion operates in O(p s) time and O(p) space within the Lighting Approximation family. Key governing relation: occlusion = blocked_samples / total_samples. Often compared with Screen Space Ambient Occlusion and Path Tracing.