The OIV.LDM.Nodes.SoMultiDataSeparator node allows you to combine multiple data sets.

This is the correct method for combining multiple data sets. Combining multiple data sets without inserting them under an OIV.LDM.Nodes.SoMultiDataSeparator node may produce incorrect results and should be avoided.

Each data set is represented by an OIV.LDM.Nodes.SoDataSet node (typically an OIV.VolumeViz.Nodes.SoVolumeData node). Combining is enabled by an OIV.LDM.Nodes.SoDataCompositor node for CPU combining or an OIV.VolumeViz.Nodes.SoVolumeShader node for GPU combining. A common use of GPU combining is to implement co-blending of multiple volumes, in other words using a fragment shader to combine the color and/or intensity values of the voxels.

Some rules must be followed when doing render or data compositing:

• Each OIV.VolumeViz.Nodes.SoVolumeData node must have a unique OIV.LDM.Nodes.SoDataSet.dataSetId.

• All the OIV.VolumeViz.Nodes.SoVolumeData nodes to be composited, as well as the compositing node (e.g. OIV.VolumeViz.Nodes.SoVolumeShader for slices or OIV.VolumeViz.Nodes.SoVolumeRenderingQuality for volumes) and the rendering node (e.g. OIV.VolumeViz.Nodes.SoVolumeRender), must be under an OIV.LDM.Nodes.SoMultiDataSeparator node.

• The OIV.VolumeViz.Nodes.SoVolumeData nodes to be composited must be all scalar data sets or all RGBA data sets. To composite scalar and RGBA data sets under the same OIV.LDM.Nodes.SoMultiDataSeparator, set the usePalettedTexture field to false in the scalar dataset's OIV.VolumeViz.Nodes.SoVolumeData node to force the scalar data to be converted into RGBA data.

• An OIV.VolumeViz.Nodes.SoVolumeData node used in a data compositing scheme must not be inserted multiple times in the scene graph. Use another volume data node pointing to the same file.

• All transfer functions must have the same 'colorMapType' and must have the same number of entries in the colormap.

Each OIV.VolumeViz.Nodes.SoVolumeData node has its own resource settings (see field OIV.LDM.Nodes.SoDataSet.ldmResourceParameters). In case of multi data combining, datas with same characteristics (volume size, tile size and same location in world coordinates) aggregate their resources to display the best resolution as possible. For example with 4 datasets VD1, VD2, VD3, VD4 that have same resource parameters but not SoLMDRessourceParameters.max2DTexMemory:

• VD1: max2DTexMemory = 1GB

• VD2: max2DTexMemory = 1GB

• VD3: max2DTexMemory = 9GB

• VD4: max2DTexMemory = 1GB If VD1 and VD3 have the same characteristics and VD2 and VD4 have other identical characteristics, in this case VD1 and VD3 will share 10 GB of 2D texture memory while VD2 and VD4 will share 2 GB only. The same rule applies for other ldm resource parameters.

GPU combining must be implemented in a shader program written in the standard GLSL language. The shader program will be specified using an OIV.VolumeViz.Nodes.SoVolumeShader node. The shader source code is loaded using (for example) an OIV.Inventor.Nodes.SoFragmentShader object. Uniform parameters for the shader may be specified using the subclasses of OIV.Inventor.Nodes.SoShaderParameter. See OIV.VolumeViz.Nodes.SoVolumeShader for more information about the shader function library provided by VolumeViz.

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. See OIV.VolumeViz.Nodes.SoVolumeShader for more details.

For each data set there will typically be an OIV.LDM.Nodes.SoDataRange node and an OIV.LDM.Nodes.SoTransferFunction node to define the mapping from data values to color values. For each OIV.VolumeViz.Nodes.SoVolumeData a separate 3D texture will be generated and sent to the GPU. 3D textures can be generated with different precision (8-bit or 12-bit) according to the OIV.LDM.Nodes.SoDataSet.texturePrecision field. The texture unit used for each data set is determined by the OIV.LDM.Nodes.SoDataSet.dataSetId field. All colormaps are aggregated into a single 2D texture.

A custom fragment shader can retrieve the voxel's data value from each 3D texture using the GLSL VolumeViz function:

VVIZ_DATATYPE value = VVizGetData( dataSetId, texCoord );

vec4 color = VVizTransferFunction( value, colorMapId );

VVizOutputColor( color ):

EXAMPLE

The following code shows how to do multidata rendering using an OIV.VolumeViz.Nodes.SoVolumeShader node to combine values for an OIV.VolumeViz.Nodes.SoVolumeRender node. Given two OIV.VolumeViz.Nodes.SoVolumeData nodes ds1 and ds2:

SoVolumeShader volumeShader = new SoVolumeShader();

SoVolumeData volumeData1 = new SoVolumeData();
volumeData1.dataSetId.Value = 0;
SoDataRange dataRange1 = new SoDataRange();
dataRange1.dataRangeId.Value = 0;
SoTransferFunction colorMap1 = new SoTransferFunction();

SoVolumeData volumeData2 = new SoVolumeData();
volumeData2.dataSetId.Value = 1;
SoDataRange dataRange2 = new SoDataRange();
dataRange2.dataRangeId.Value = 1;
SoTransferFunction colorMap2 = new SoTransferFunction();

SoVolumeRender volumeRender = new SoVolumeRender();

SoMultiDataSeparator multiDataSep = new SoMultiDataSeparator();
   multiDataSep.AddChild( volumeShader ); // Shader to combine volumes

   multiDataSep.AddChild( volumeData1 );
   multiDataSep.AddChild( dataRange1 );
   multiDataSep.AddChild( colorMap1 );

   multiDataSep.AddChild( volumeData2 );
   multiDataSep.AddChild( dataRange2 );
   multiDataSep.AddChild( colorMap2 );

   multiDataSep.AddChild( volumeRender );
root.AddChild(multiDataSep);

Reference