Note: This documentation is for the development version of X3DOM. Released versions: 1.5, 1.4, 1.3, 1.2.

Culling

This tutorial explains the different parameters to adjust x3doms integrated culling techniques for your personal needs on quality and performance.

The Environment-Bindable

All relevant parameters are included in the new Environment-Bindable. To change it’s settings it has to be added to the scene explicitly. For each culling technique there exists a boolean flag to enable/disable it and a list of more detailed settings if applicable. Each of the following sections explains the usage of a technique and it’s parameters. Their combination can lead to very different results which allows explicit performance tuning for a specific scene.

<environment frustumCulling='true' smallFeatureCulling='true'>
</environment>

View Frustum Culling

The most common culling technique is the viewfrustum culling controlled by the viewFrustumCulling flag. The bounding volumes of the nodes are tested to be intersecting the frustum defining the current view. The nodes of the scene are traversed recursively reusing already calculated intersection if possible. It is the only technique which is not dependent on additional parameters.

Setting Usage Values
frustumCulling (de-)activate the culling technique [true;false]

Small Feature Culling

Using the smallFeatureCulling flag this technique is activated. For each node the amount of pixels is calculated it’s bounding volume would cover in screen space. If the coverage is below the smallFeatureThreshold parameter the node (and subsequent shapes) is culled.

Setting Usage Values
smallFeatureCulling (de-)activate the culling technique [true;false]
smallFeatureTreshold cull objects covering less pixels than treshold [0..*]

Occlusion Culling *

Being the most complex supported culling method, occlusion culling is triggered by the occlusionCulling flag. The scene is traversed using the “Coherent Hierarchical Culling++” algorithm and based on the triggere occlusion queries the screen space coverage not occluded by other nodes is tested. A node is only drawn if its coverage is higher than the occlusionVisibilityTreshold.

Setting Usage Values
occlusionCulling (de-)activate the culling technique [true;false]
occlusionVisibilityTreshold cull objects covering less pixels than treshold due to occlusion [0..*]

Low Priority Culling

This is the only supported comparison-based culling technique. Triggered by the lowPriorityCulling the nodes which passed all previous (activated) culling techniques are sorted by their priority. Afterwards the part of this list defined by the lowPriorityTreshold is removed. At the moment the screen-space coverage is used as priority, later on there will be a more sophisticated calculation allowing the user to set priorities to mark his or her personally important nodes. Therefore by now the priority culling is very similar to the small feature method but culling a relative amount instead of comparing to an absolute threshold.

Setting Usage Values
lowPriorityCulling (de-)activate the culling technique [true;false]
lowPriorityThreshold draw only objects within threshold fraction of priority sorted list [0..1]

Tesselation Detail Culling

The possibiliy of using this culling technique completely depends on the support of each drawable. Up to now only the POP-Geometry natively supports it. As long as the resulting error stays within the amount of pixels defined by tesselationErrorThreshold the tesselation of the mesh is lowered to certain degree. It can be enabled using the flag tesselationDetailCulling.

Setting Usage Values
tesselationDetailCulling (de-)activate the culling technique [true;false]
tesselationErrorTreshold use mesh simplification having lower error than threshold [0..*]

(* : Not fully implemented yet)