Class SoFenceSlice

  • All Implemented Interfaces:

    public class SoFenceSlice
    extends SoSlice
    Fence slice shape node. This node renders a strip (connected series) of slices. The strip is defined by a set of 2D vertices that form a polyline. Each segment of the polyline is extruded along the axis specified in the axis field to form (in effect) an oblique slice. The default axis is Z, so the 2D points are treated as (X,Y) values. The points may be outside the 3D extent of the volume, but only the portion of the slice inside the volume will be drawn (subject to region of interest and other clipping nodes).

    The SoVolumeData node on which this shape is applied can be specified with dataSetId. When this field is set to 0, the last SoVolumeData node on state is used.

    A similar effect could be obtained using volume geometry (e.g. SoVolumeFaceSet), but SoFenceSlice is more convenient and is optimized for this specific case.

    The 2D coordinates are interpreted according to the following table. See the code example below.

      Fence axis Coordinate axes
      X Y , Z
      Y Z , X
      Z X , Y

    For a non-RGBA (scalar valued) volume, each voxel's RGBA value is determined by the current SoDataRange and SoTransferFunction. The current diffuse color and transparency (set, for example, with an SoMaterial node) modify the appearance of the slice. This means that, for example, the current transparency can be used as a global alpha value to modulate the overall opacity of the slice. For an RGBA volume each voxel's RGBA value comes directly from the volume data.

    The interpolation field controls how the texture is interpolated.

    The alphaUse field (SoSlice) controls how the voxel's alpha component is used when drawing the fence slice.

    Optionally a bump mapping effect may be applied. Normal vectors are automatically computed from the data value gradient. The enableBumpMapping and bumpScale fields (SoSlice) control whether bump mapping is active and the intensity of the effect.


    • Transformation matrices:
      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 visualization nodes. However the same transformation must be applied to the volume data node and all volume visualization nodes associated with that volume. So effectively any transformation nodes that affect the volume must be placed before the volume data node.
    • Picking:
      The entire slice is pickable, even where it is transparent as a result of the current transfer function. Currently SoFenceSlice does not provide an SoDetail object.
    • Interpolation:
      Interpolation is specified using the interpolation field. The default (LINEAR) does bi-linear interpolation between voxel values. The NEAREST value can be used to display individual voxels. For best image quality we recommend using the MULTISAMPLE_12 value.
    • Data range:
      By default VolumeViz maps the entire range of the voxel's data type (e.g. 0..65535 for unsigned short) into the colormap. This is often correct for byte (8 bit) voxels, but seldom correct for 16 bit voxels and never correct for floating point voxels. Use an SoDataRange node to specify the actual (or desired) range of data values to be mapped. Also use an SoDataRange node to implement brightness/contrast control like the Window/Level setting commonly used with medical images.
    • Clipping:
      Volume primitives can be clipped using a region of interest (SoROI), geometry (SoVolumeClippingGroup) and/or height fields (SoUniformGridClipping). They are also clipped by OpenGL clipping planes (SoClipPlane), but we recommend using the VolumeViz clipping nodes instead.
    • Material:
      The color of each voxel is modulated by the current diffuse color in the traversal state. The default diffuse color is 0.8,0.8,0.8. This results in full intensity values in the color map being displayed as 80% intensity. Therefore we recommend adding an SoMaterial node before the slice and setting its diffuseColor field to full white (1,1,1).
    • Transparency:

      • Typically the color map (SoTransferFunction) used for volume rendering (SoVolumeRender) assigns transparency (alpha < 1) to some voxel values. If you want to use the same color map for slice rendering, but render the slice completely opaque, set the alphaUse field to ALPHA_OPAQUE. This overrides the alpha values in the color map (or an RGBA volume). However it does not affect transparency assigned using an SoMaterial node.

      • If you want to adjust the overall transparency of the slice, add an SoMaterial node and set its transparency field (keeping alphaUse set to ALPHA_AS_IS). Effectively a scale factor 1-transparency is applied to each voxel's alpha value.

      • Intersecting transparent slices cannot be rendered correctly by the basic blending transparency algorithms. To render this case correctly, set the transparency algorithm to SORTED_PIXEL using the viewer class or SoGLRenderAction.
    • Voxel edges:
      The edges of the voxels can also be rendered. See options in the SoVolumeRenderingQuality node.
    • Custom shaders:
      The current SoVolumeShader node, if any, allows custom shaders to be defined for special computation or rendering effects, including blending multiple volumes.
    • 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,
       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 SoTransformation nodes that are placed before the SoDataSet node in the order of the traversal.
    • Performance:
      • Tile size:
        For backward compatibility, the default tile size is still only 64. This is quite small for modern CPU/GPU hardware. The smaller the tile size, the larger the total number of tiles that must be managed by VolumeViz. This overhead can be significant, especially for operations that require reloading the data textures on the GPU, for example, changing the data range (SoDataRange). For smaller volumes, like 512^3, it can be efficient to set the tile size large enough to contain the entire volume. For very large volumes, larger tile sizes are efficient for SoVolumeRender but somewhat inefficient for slice rendering because complete tiles must be loaded even though the slice only uses part of the data. Applications should experiment.
        For volumes stored in LDM file format, the tile size must be specified when the volume is converted to LDM (see SoConverter and the "-t" option). For other data data formats the tile size can be specified using the SoVolumeData node's ldmResourceParameters field, but only after setting the filename field or calling the setReader() method.
      • Tile cache policy: It specifies how the tiles are stored in CPU memory. The selected policy can significantly impact the data loading performance versus the CPU memory footprint. See SoLDMResourceParameters.tileCachePolicy for detail.
    • Hardware requirements:
      This node needs a graphic card with support for GLSL shader, vertex buffer objects (VBO) and framebuffer object (FBO). Use the isSupported() method to check if the current graphics board can render a FenceSlice.


    Please see SoObliqueSlice for a complete code example. The following shows how to set up the axis and points fields of SoFenceSlice.

     SoFenceSlice fenceSlice = new SoFenceSlice();
       fenceSlice.axis.setValue( SoFenceSlice.AxisType.Y );
       fenceSlice.points.set1Value( 0, new SbVec2f(-0.2f, -0.66f) );
       fenceSlice.points.set1Value( 1, new SbVec2f( 0.2f, -0.4f ) );
       fenceSlice.points.set1Value( 2, new SbVec2f(-0.2f,  0.4f ) );
       fenceSlice.points.set1Value( 3, new SbVec2f( 0.2f,  0.66f) );

      Fence slice on Y axis (Colt example data set):
      Fence slice on X axis (Colt example data set):
      Fence slice on Z axis (Colt example data set):

    File format/default:

    FenceSlice {

      dataSetId 0
      points [ ]
      axis Z
      interpolation LINEAR
      alphaUse ALPHA_BINARY
      useRGBA false
      alternateRep NULL
      enableBumpMapping false
      bumpScale 1.0

    Action behavior:

    Draws a textured shape based on current SoVolumeData, SoTransferFunction, and SoROI nodes.

    Computes the bounding box that encloses the fence slice.

    See Also:
    SoVolumeData, SoDataRange, SoTransferFunction, SoROI, SoSlice, SoObliqueSlice, SoOrthoSlice, SoFenceSliceDetail
    • Field Detail

      • dataSetId

        public final SoSFInt32 dataSetId
        Specifies the SoVolumeData node to use. This is useful when datasets of different dimensions are present in the scene graph. Please see SoMultiDataSeparator for more details.

        When set to 0, the last SoVolumeData node on state is used. Default is 0.

        Open Inventor 10.11.0

      • points

        public final SoMFVec2f points
        Set of points defining a lineset.
        If axis is:
        • X: points are Y,Z coordinates
        • Y: points are Z,X coordinates
        • Z: points are X,Y coordinates

        All points should be inside the 3D extent of the volume.

    • Constructor Detail

      • SoFenceSlice

        public SoFenceSlice()
    • Method Detail

      • isSupported

        public static boolean isSupported()
        Calls isSupported((com.openinventor.inventor.misc.SoState)null).
      • isSupported

        public static boolean isSupported​(SoState state)
        Returns true if graphic card can render an SoFenceSlice. GPU must support GLSL. When using a debug build of Open Inventor, some "no context available" warning messages may be generated. You can ignore them or see SoGLExtension for an example of using SoGLContext to avoid them.