SoBufferedShape is useful to manage the rendering of large geometry, provide application control over where the data is stored (CPU or GPU) and to integrate rendering with the Open Inventor computing framework (through the SoBufferObject classes).

SoBufferedShape provides fields for:

• Vertices

• Indices (optional)

• Colors (optional)

• Normals (optional)

• Texture coordinates (optional)

In this sense it is similar to the SoVertexProperty node, but SoVertexProperty is just a property node. SoBufferedShape also does the rendering of the shape. Properties that are not specified are taken from the traversal state (e.g. colors) or computed (e.g. normals).

SoBufferedShape can render many types of geometric primitives including points, lines, quads and triangles. (A single type must be specified per instance of SoBufferedShape.) You specify the type of primitive in the SoSFEnum field shapeType.

SoBufferedShape can render multiple primitives of the same type. You can specify the number of vertices (or indices if provided) to use for each primitive in the SoMFInt32 field numVertices (similar to SoFaceSet).

You can also use the primitive restart feature to define multiple indexed strip shapes, for example TRIANGLE_STRIP or LINE_STRIP. The end of each primitive is marked by a special index value in the index buffer and this value can be specified in the primitiveRestartValue field. The behavior is similar to the "-1" value that can be used in Open Inventor indexed shape nodes like SoIndexedFaceSet, but is implemented on the GPU. NOTE:

• Primitive restart must be explicitly enabled using the primitiveRestartEnabled field.

• Check availability of primitive restart using SoShape.isPrimitiveRestartAvailable().

The geometry and its attributes must be stored in buffer objects (see SoBufferObject). The buffer objects can be SoGLBufferObjects stored directly on the graphics board or SoCpuBufferObjects stored in system memory. This allows the application to control what data is stored where.

If lighting is enabled (there is no SoLightModel node or the model field of the SoLightModel is set to PHONG) and the normalBuffer field is not set, then Open Inventor will automatically compute normal vectors, but only in some cases (see Limitations section). Normal generation is affected by the creaseAngle field of the SoShapeHints node, but only if the vertices are NOT indexed (indexBuffer field is not set). If the vertices are indexed the creaseAngle is forced to PI, creating a smooth surface rendering. If the application needs to render sharp edges on a shape, either compute normal vectors and set the normalBuffer field or do not use the indexBuffer field. It is possible to disable normal generation (if for example the normals are generated by a geometry shader) by setting the useNormalsGenerator field to false. If no normal vectors are specified or generated, and lighting is enabled, the primitive may not be rendered correctly.

SoBufferedShape provides fields to describe the content of each buffer, e.g. the data type and number of components in each buffer, as well as how to access the buffers, e.g. the offset into the buffer and "stride" separating data values in the buffer. The default values for offset and stride assume that the vertices, normals, etc are each in a separate buffer. However setting appropriate offset and stride allows, for example, vertices and normals to be interleaved in a single buffer. In this case the same buffer would be set into both the vertexBuffer and normalBuffer fields.

To disable computing the bounding box, which can take a long time with very large geometry, use the SoBBox node to specify a pre-computed bounding box.

Limitations

• Transparency: If there is no color buffer, making the entire shape transparent using an SoMaterial node works as usual. However if there is a color buffer with RGBA values, note that Open Inventor does not currently check the color buffer for transparency (alpha values < 1). So in this case the SoBufferedShape will not be considered transparent geometry (even if there are alpha values < 1) and may not be rendered correctly. You can force Open Inventor to handle the shape as transparent geometry by putting an SoMaterial node with non-zero transparency before it in the scene graph.

• Normal generation: If lighting is enabled and the normalBuffer field is not set, then Open Inventor will automatically compute normal vectors, but only in some cases. Automatic generation of normal vectors is ONLY enabled when:

  • The vertexComponentsCount field is set to 3 (default),

  • The vertexComponentsType field is set to SbDataType.FLOAT (default),

  • The primitiveRestartEnabled field is set to false (default), and

  • The primitives are TRIANGLES, TRIANGLE_STRIP or QUADS. Note: The crease angle (see SoShapeHints) is not used by the normal generator if the vertices are indexed. If the application needs to render sharp edges on a shape, either compute normal vectors and set the normalBuffer field or do not use the indexBuffer field.

• SoGetPrimitiveCountAction: When using the primitive restart feature, the triangle/line count returned by the SoGetPrimitiveCountAction will not be accurate.

• Concave polygons: Unlike (for example) SoFaceSet, SoBufferedShape does NOT automatically tesselate concave or complex polygons. Such primitives may not be rendered correctly.

• SoWriteAction: SoBufferedShape can be saved to and restored from a .iv file just like any other Open Inventor node. However, during the read operation any OpenGL buffer objects (SoGLBufferObject) in the file will be created as CPU buffers (SoCpuBufferObject) if there is no OpenGL context bound during the read operation.

• Material binding (etc): SoBufferedShape effectively only supports per-vertex and per-vertex-indexed binding of materials, normals and texture coordinates using the values found in its own buffers.

• Simplification: SoBufferedShape is currently ignored by the "simplify" actions (SoShapeSimplifyAction, SoGlobalSimplifyAction, SoReorganizeAction).

Example using CPU buffer:

float[] vertices = new float[9 * 3] {
       1.0f, 0.5f,0.0f, 0.0f, 1.0f,0.0f, -1.0f,0.5f,0.0f,
      -1.0f,-1.0f,0.0f, 1.0f,-1.0f,0.0f,  1.0f,0.0f,0.0f, -1.0f,0.0f,0.0f,
      -1.0f,-1.5f,0.0f, 1.0f,-1.5f,0.0f
};
Int32[] numVerts = new Int32[3] { 3, 4, 2 };

SbNativeArray<float> vertArray = new SbNativeArray<float>(vertices);
SoCpuBufferObject   vertBuffer = new SoCpuBufferObject((SbNativeArray<byte>)vertArray);

SoBufferedShape shape = new SoBufferedShape();
shape.shapeType.SetValue( "LINE_STRIP" );
shape.numVertices.SetValues( 0, numVerts );
shape.vertexBuffer.Value = vertBuffer;

Example using GPU buffer:

float[] vertices = new float[9 * 3] {
   1.0f, 0.5f,0.0f, 0.0f, 1.0f,0.0f, -1.0f,0.5f,0.0f,
   -1.0f,-1.0f,0.0f, 1.0f,-1.0f,0.0f,  1.0f,0.0f,0.0f, -1.0f,0.0f,0.0f,
   -1.0f,-1.5f,0.0f, 1.0f,-1.5f,0.0f
};
Int32[] numVerts = new Int32[3] { 3, 4, 2 };


SbNativeArray<float> vertArray = new SbNativeArray<float>(vertices);
SoCpuBufferObject vertBuf = new SoCpuBufferObject( (SbNativeArray<byte>)vertArray );

SoGLContext glContext = new SoGLContext(true);
glContext.Bind();
   SoGLBufferObject gpuBuffer = new SoGLBufferObject(SoGLBufferObject.Usages.STATIC_DRAW);
   gpuBuffer.SetTarget( SoGLBufferObject.BufferObjectTargets.ARRAY_BUFFER );
   gpuBuffer.SetSize( cpuBuffer.GetSize() );  // Set the buffer size (allocate memory)
   gpuBuffer.Memcpy ( cpuBuffer );            // Copy data into the buffer
glContext.Unbind();

SoBufferedShape shape = new SoBufferedShape();
shape.shapeType.SetValue("LINE_STRIP");
shape.numVertices.SetValues(0, numVerts);
shape.vertexBuffer.Value = gpuBuffer;
root.AddChild(shape);

LIMITATIONS: SoBufferedShape needs a graphic card supporting vertex buffer objects, if not available shape won't be rendered.

FILE FORMAT/DEFAULT

BufferedShape {

useNormalsGenerator	true
shapeType	TRIANGLES
numVertices	0
vertexBuffer	NULL
vertexComponentsCount	3
vertexComponentsType	SbDataType.FLOAT
vertexStride	0
vertexOffset	0
normalBuffer	NULL
normalComponentsType	SbDataType.FLOAT
normalStride	3 * sizeof(float)
normalOffset	0
indexBuffer	NULL
indexType	SbDataType.UNSIGNED_INT32
indexOffset	0
colorBuffer	NULL
colorComponentsType	SbDataType.FLOAT
colorStride	0
colorOffset	0
colorComponentsCount	3
texCoordsBuffer	NULL
texCoordsComponentsType	SbDataType.FLOAT
texCoordsStride	0
texCoordsOffset	0
texCoordsComponentsCount	2
primitiveRestartEnabled	false
primitiveRestartValue	-1

}

ACTION BEHAVIOR

SoGLRenderAction, SoCallbackAction, SoBoundingBoxAction Do the actual rendering / bounding box computation.

Reference