SoPostEffectAmbientOcclusion

InventorModule

author	MeVis Medical Solutions AG
package	MeVisLab/Standard
dll	SoRenderers
definition	SoRenderers.def

Purpose

The SoPostEffectAmbientOcclusion module offers screen space ambient occlusion (SSAO) for the

SoPostEffectRenderer module.

This module only works on opaque geometry, so it should be placed before any transparent geometry rendered by SoPostEffectAdditionalGeometry modules.

It makes use of the depth and normal buffers to calculate the ambient occlusion in screen space.

Details

The algorithm contains various parameters, the best setting for the parameter highly depends on the concrete geometry that is rendered.

Example screenshots:

Normal Rendering:

With Screen Space Ambient Occlusion turned on:

Only the ambient occlusion term:

Parameter Fields

Field Index

Angle Bias: Float	Mode (mode): Enum	Show Ambient Only: Bool
Attenuation: Float	Mode (blurMode): Enum
Contrast: Float	Num. Directions: Integer
debugTextures: Bool	Num. Steps: Integer
Enable: Bool	Radius: Float
Enabled: Bool	Sample Radius: Float
Half resolution ambient occlusion: Bool	Scale: Float
Intensity: Float	Sharpness: Float

Visible Fields

Enabled

name: enabled, type: Bool, default: TRUE

If checked, the effect is enabled.

Angle Bias

name: ambientAngleBias, type: Float, default: 30, minimum: 0, maximum: 60

Sets an angle threshold.

All angles below this threshold (in degrees) will be discarded when calculating ambient occlusion.

Thus, the higher this value, the less self-occlusion will occur. The optimal value for this parameter depends on the coarseness of the triangle mesh: the coarser the mesh, the greater the bias should be.

Sample Radius

name: ambientSampleRadius, type: Float, default: 30

Sets the radius of the SSAO sampling.

Intensity

name: ambientIntensity, type: Float, default: 8, minimum: 0.1, maximum: 16

Sets the intensity of the ambient occlusion.

Scale

name: ambientScale, type: Float, default: 0.1, minimum: 0.0001, maximum: 1

Sets a scaling factor for the distance term of the algorithm; lower values produce more occlusion.

Num. Directions

name: ambientNumDirs, type: Integer, default: 16, minimum: 1, maximum: 25

Sets how many occlusion directions are considered for each screen pixel.

This value is considered only if Mode is set to SSAO_HIGH_QUALITY.

Num. Steps

name: ambientNumSteps, type: Integer, default: 8, minimum: 1, maximum: 32

Sets how many steps are sampled on each direction.

This value is considered only if Mode is set to SSAO_HIGH_QUALITY.

Attenuation

name: ambientAttenuation, type: Float, default: 1, minimum: 0, maximum: 1

Sets the attenuation of the ambient occlusion term.

This value is considered only if Mode is set to SSAO_HIGH_QUALITY.

Contrast

name: ambientContrast, type: Float, default: 1.25, minimum: 0, maximum: 3

Sets the contrast of the ambient occlusion term.

This value is considered only if Mode is set to SSAO_HIGH_QUALITY.

Enable

name: blurPass, type: Bool, default: TRUE

If checked, an additional blur pass is enabled.

Half resolution ambient occlusion

name: useLowResAO, type: Bool, default: FALSE

If checked, the SSAO calculation and blur pass is using a half-resolution buffer.

Show Ambient Only

name: showAmbientOnly, type: Bool, default: FALSE

If checked, the SSAO term is rendered.

Mode (mode)

name: mode, type: Enum, default: SSAO_HIGH_QUALITY

Defines the quality mode.

Using high quality is recommended, but it is substantially slower.

Values:

Title	Name	Description
​Low Quality	​SSAO_LOW_QUALITY	​Implements a simplified version of the original Nvidia algorithm, which is much faster but less precise/correct.
​High Quality	​SSAO_HIGH_QUALITY	​Implements “Horizon Based Ambient Occlusion” For more details, see here This software contains source code provided by NVIDIA Corporation.

Mode (blurMode)

name: blurMode, type: Enum, default: BILATERAL_BLUR

Defines the blur mode.

Values:

Title	Name	Description
​Bilateral Blur	​BILATERAL_BLUR	​Uses a bilateral blur filter that is edge preserving.
​Gaussian 9x9	​GAUSSIAN_9x9	​Uses a simple 9x9 Gauss filter to blur the ambient occlusion term.

Radius

name: blurRadius, type: Float, default: 9, minimum: 2, maximum: 16

Sets the radius of the blur filter.

Sharpness

name: blurSharpness, type: Float, default: 1, minimum: 0.1, maximum: 2

Sets the sharpness of the filter, aiming to avoid blurring edges with a large depth difference.

Hidden Fields

debugTextures

name: debugTextures, type: Bool, default: FALSE