This node defines a shape which is the intersection of the volume data defined by an OIV.VolumeViz.Nodes.SoVolumeData node and the 3D shape formed by constructing faces (polygons) from vertices located at the coordinates specified in the vertexProperty field (from OIV.Inventor.Nodes.SoVertexShape) or the current inherited state. For optimal performance, use of the vertexProperty field is recommended.

The shape defined by this intersection is textured using the data from the current OIV.VolumeViz.Nodes.SoVolumeData node and OIV.LDM.Nodes.SoTransferFunction node. The OIV.VolumeViz.Nodes.SoVolumeFaceSet.interpolation field controls how the texture is interpolated. Texture coordinates are automatically computed for each vertex based on its position relative to the 3D extent of the volume. If texture coordinates are specified, they are ignored.

This node can be used to create custom "slices" through the volume, for example a cylinder slice. It can be considered a generalization of the OIV.VolumeViz.Nodes.SoOrthoSlice, OIV.VolumeViz.Nodes.SoObliqueSlice, OIV.VolumeViz.Nodes.SoFenceSlice, etc features. But note:

• Compared to an equivalent standard slice (e.g. OIV.VolumeViz.Nodes.SoOrthoSlice), the rendering may be slightly different due to positioning and interpolation.

• The standard slices (e.g. OIV.VolumeViz.Nodes.SoOrthoSlice) have "two-sided lighting" enabled by default as a convenience. This is not true for volume geometry nodes (which have the same default as their corresponding standard geometry node), so the "back" side of the geometry will not be lighted unless you enable two-sided lighting using an OIV.Inventor.Nodes.SoShapeHints node.

When set to false, the OIV.VolumeViz.Nodes.SoVolumeFaceSet.clipGeometry field allows rendering of the portion of the geometry that does not intersect the volume data. This portion is not textured and is rendered as a regular OIV.Inventor.Nodes.SoFaceSet.

This node uses 3D texturing and is not available if the hardware does not support this feature.

OIV.VolumeViz.Nodes.SoVolumeFaceSet uses the coordinates in order, starting with the first one. Each face has a number of vertices specified by a value in the numVertices field. For example, an OIV.VolumeViz.Nodes.SoVolumeFaceSet with numVertices of [3,4,4] would use coordinates 1, 2, and 3 for the first face, coordinates 4, 5, 6, and 7 for the second face, and coordinates 8, 9, 10, and 11 for the third. For improved performance, arrange all the faces with only 3 vertices at the beginning of the list, then all faces with 4 vertices, and finally all other faces.

The number of values in the numVertices field indicates the number of faces in the set.

The coordinates of the face set are transformed by the current cumulative transformation. The faces are drawn with the current light model and drawing style.

Treatment of the current material and normal binding is as follows: The PER_PART and PER_FACE bindings specify a material or normal for each face. The _INDEXED bindings are equivalent to their non-indexed counterparts. The default material binding is OVERALL. The default normal binding is PER_VERTEX.

If any normals (or materials) are specified, Open Inventor assumes you have provided the correct number of them, as indicated by the binding. You will see unexpected results if you specify fewer normals (or materials) than the shape requires. If no normals are specified, they will be generated automatically.

Notes:

• A face set may render or pick incorrectly if any of its polygons are self-intersecting or non-planar.

• The volume size and orientation (like geometry) can be modified by transformation nodes in the scene graph and this in turn modifies the appearance of volume rendering nodes like OIV.VolumeViz.Nodes.SoVolumeFaceSet. However the same transformation must be applied to the volume data node and all volume rendering nodes associated with that volume. So effectively any transformation nodes that affect the volume must be placed before the volume data node.

• For performance concerns, an instance of OIV.VolumeViz.Nodes.SoVolumeFaceSet should not be used multiple times in the scene graph. In order to have the best trade-off between performances and memory footprint use a single OIV.Inventor.Nodes.SoVertexProperty node shared by several instances of OIV.VolumeViz.Nodes.SoVolumeFaceSet.

• Composition with Multiple Data: It is possible to compose datasets that have different dimensions, tile sizes and transformations. In order to help fetch the correct data values in custom shaders, texture coordinates conversion functions are provided in the VolumeViz/vvizStructure.h shader include. For instance,

  Copy

  vec3 VVizTextureToTextureVec(in VVizDataSetId datasetSrc, in VVizDataSetId datasetDst, in vec3 texCoord);

  can be used to convert texture coordinates related to one dataset to texture coordinates related to another dataset. The conversion is based solely on the transformations applied to each dataset, which are defined by their model matrix and their extent. Please note that the model matrix of a dataset is defined by to the OIV.Inventor.Nodes.SoTransformation nodes that are placed before the OIV.LDM.Nodes.SoDataSet node in the order of the traversal.

FILE FORMAT/DEFAULT

VolumeFaceSet {

vertexProperty	NULL
startIndex	0
numVertices	-1
clipGeometry	true
offset	0
interpolation	LINEAR

}

ACTION BEHAVIOR

OIV.Inventor.Actions.SoGLRenderAction Draws faces based on the current coordinates, normals, materials, drawing style, and so on.

OIV.Inventor.Actions.SoRayPickAction Picks faces based on the current coordinates and transformation. Details about the intersection are returned in an OIV.Inventor.Details.SoFaceDetail.

OIV.Inventor.Actions.SoGetBoundingBoxAction Computes the bounding box that encloses all vertices of the face set with the current transformation applied to them. Sets the center to the average of the coordinates of all vertices.

OIV.Inventor.Actions.SoCallbackAction If any triangle callbacks are registered with the action, they will be invoked for each successive triangle generated from each face in the set.

Reference