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NAME

       SoVRMLBillboard -

       The SoVRMLBillboard class is used for rotating geometry towards the viewpoint.

       The detailed class documentation is taken verbatim from the VRML97 standard (ISO/IEC
       14772-1:1997). It is copyright The Web3D Consortium, and is used by permission of the
       Consortium:

SYNOPSIS

       #include <Inventor/VRMLnodes/SoVRMLBillboard.h>

       Inherits SoVRMLParent.

   Public Member Functions
       SoVRMLBillboard (void)
       SoVRMLBillboard (int numchildren)
       virtual void doAction (SoAction *action)
       virtual void callback (SoCallbackAction *action)
       virtual void GLRender (SoGLRenderAction *action)
       virtual void getBoundingBox (SoGetBoundingBoxAction *action)
       virtual void getMatrix (SoGetMatrixAction *action)
       virtual void pick (SoPickAction *action)
       virtual void search (SoSearchAction *action)
       virtual void GLRenderBelowPath (SoGLRenderAction *action)
       virtual void GLRenderInPath (SoGLRenderAction *action)
       virtual void GLRenderOffPath (SoGLRenderAction *action)
       virtual void notify (SoNotList *list)

   Static Public Member Functions
       static void initClass (void)

   Public Attributes
       SoSFVec3f axisOfRotation
       SoSFVec3f bboxCenter
       SoSFVec3f bboxSize

   Protected Member Functions
       virtual ~SoVRMLBillboard ()

Detailed Description

       The SoVRMLBillboard class is used for rotating geometry towards the viewpoint.

       The detailed class documentation is taken verbatim from the VRML97 standard (ISO/IEC
       14772-1:1997). It is copyright The Web3D Consortium, and is used by permission of the
       Consortium:

         Billboard {
           eventIn      MFNode   addChildren
           eventIn      MFNode   removeChildren
           exposedField SFVec3f  axisOfRotation 0 1 0     # (-inf, inf)
           exposedField MFNode   children       []
           field        SFVec3f  bboxCenter     0 0 0     # (-inf, inf)
           field        SFVec3f  bboxSize       -1 -1 -1  # (0, inf) or -1,-1,-1
         }
         .fi

       The Billboard node is a grouping node which modifies its coordinate system so that the Billboard node's local Z-axis turns to point at the viewer. The Billboard node has children which may be other children nodes. The axisOfRotation field specifies which axis to use to perform the rotation. This axis is defined in the local coordinate system. When the axisOfRotation field is not (0, 0, 0), the following steps describe how to rotate the billboard to face the viewer:

       · a. Compute the vector from the Billboard node's origin to the viewer's position. This vector is called the billboard-to-viewer vector.
       · b. Compute the plane defined by the axisOfRotation and the billboard-to-viewer vector.
       · c. Rotate the local Z-axis of the billboard into the plane from b., pivoting around the axisOfRotation.
       When the axisOfRotation field is set to (0, 0, 0), the special case of viewer-alignment is indicated. In this case, the object rotates to keep the billboard's local Y-axis parallel with the Y-axis of the viewer. This special case is distinguished by setting the axisOfRotation to (0, 0, 0). The following steps describe how to align the billboard's Y-axis to the Y-axis of the viewer:
       · d. Compute the billboard-to-viewer vector.
       · e. Rotate the Z-axis of the billboard to be collinear with the billboard-to-viewer vector and pointing towards the viewer's position.
       · f. Rotate the Y-axis of the billboard to be parallel and oriented in the same direction as the Y-axis of the viewer.
       If the axisOfRotation and the billboard-to-viewer line are coincident, the plane cannot be established and the resulting rotation of the billboard is undefined. For example, if the axisOfRotation is set to (0,1,0) (Y-axis) and the viewer flies over the billboard and peers directly down the Y-axis, the results are undefined. Multiple instances of Billboard nodes (DEF/USE) operate as expected: each instance rotates in its unique coordinate system to face the viewer. Subclause 4.6.5, Grouping and children nodes (<http://www.web3d.org/x3d/specifications/vrml/ISO-IEC-14772-VRML97/part1/concepts.html#4.6.5>), provides a description of the children, addChildren, and removeChildren fields and eventIns. The bboxCenter and bboxSize fields specify a bounding box that encloses the Billboard node's children. This is a hint that may be used for optimization purposes. The results are undefined if the specified bounding box is smaller than the actual bounding box of the children at any time. A default bboxSize value, (-1, -1, -1), implies that the bounding box is not specified and if needed shall be calculated by the browser. A description of the bboxCenter and bboxSize fields is contained in 4.6.4, Bounding boxes (<http://www.web3d.org/x3d/specifications/vrml/ISO-IEC-14772-VRML97/part1/concepts.html#4.6.4>),
       The rest of this class documentation is not from the VRML97 standards documentation, but was written specifically for the Coin3D API documentation.
       The following example VRML scene is a simple illustration of how SoVRMLBillboard::axisOfRotation constrains rotation around the given vector:
         #VRML V2.0 utf8

         Transform {
            translation -2 0 0
            children [
               Billboard {
                 children [ Box { } ]
               }
            ]
         }

         Transform {
            translation 2 0 0
            children [
               Billboard {
                 axisOfRotation 0 1 0
                 children [ Box { } ]
               }
            ]
         }

         Transform {
            translation 0 -2 0
            children [ Box { size 10 0.1 10 } ]
         }
         .fi

Constructor & Destructor Documentation

   SoVRMLBillboard::SoVRMLBillboard (void) Constructor.
   SoVRMLBillboard::SoVRMLBillboard (intnumchildren) Constructor. numchildren is the expected
       number of children.
   SoVRMLBillboard::~SoVRMLBillboard () [protected, virtual] Destructor.

Member Function Documentation

   void SoVRMLBillboard::initClass (void) [static] Sets up initialization for data common to all
       instances of this class, like submitting necessary information to the Coin type system.
       Reimplemented from SoVRMLParent.
   void SoVRMLBillboard::doAction (SoAction *action) [virtual] This function performs the typical
       operation of a node for any action.
       Reimplemented from SoVRMLParent.
   void SoVRMLBillboard::callback (SoCallbackAction *action) [virtual] Action method for
       SoCallbackAction.
       Simply updates the state according to how the node behaves for the render action, so the
       application programmer can use the SoCallbackAction for extracting information about the
       scene graph.
       Reimplemented from SoGroup.
   void SoVRMLBillboard::GLRender (SoGLRenderAction *action) [virtual] Action method for the
       SoGLRenderAction.
       This is called during rendering traversals. Nodes influencing the rendering state in any
       way or who wants to throw geometry primitives at OpenGL overrides this method.
       Reimplemented from SoGroup.
   void SoVRMLBillboard::getBoundingBox (SoGetBoundingBoxAction *action) [virtual] Action method
       for the SoGetBoundingBoxAction.
       Calculates bounding box and center coordinates for node and modifies the values of the
       action to encompass the bounding box for this node and to shift the center point for the
       scene more towards the one for this node.
       Nodes influencing how geometry nodes calculates their bounding box also overrides this
       method to change the relevant state variables.
       Reimplemented from SoGroup.
   void SoVRMLBillboard::getMatrix (SoGetMatrixAction *action) [virtual] Action method for
       SoGetMatrixAction.
       Updates action by accumulating with the transformation matrix of this node (if any).
       Reimplemented from SoGroup.
   void SoVRMLBillboard::pick (SoPickAction *action) [virtual] Action method for SoPickAction.
       Does common processing for SoPickAction action instances.
       Reimplemented from SoGroup.
   void SoVRMLBillboard::search (SoSearchAction *action) [virtual] Action method for
       SoSearchAction.
       Compares the search criteria from the action to see if this node is a match. Searching is
       done by matching up all criteria set up in the SoSearchAction -- if any of the requested
       criteria is a miss, the search is not deemed successful for the node.
       See also:
           SoSearchAction
       Reimplemented from SoVRMLParent.
   void SoVRMLBillboard::GLRenderBelowPath (SoGLRenderAction *action) [virtual] Implements the
       SoAction::BELOW_PATH traversal method for the rendering action.
       Reimplemented from SoNode.
   void SoVRMLBillboard::GLRenderInPath (SoGLRenderAction *action) [virtual] Implements the
       SoAction::IN_PATH traversal method for the rendering action.
       Reimplemented from SoNode.
   void SoVRMLBillboard::GLRenderOffPath (SoGLRenderAction *action) [virtual] Implements the
       SoAction::OFF_PATH traversal method for the rendering action.
       Reimplemented from SoNode.
   void SoVRMLBillboard::notify (SoNotList *l) [virtual] Notifies all auditors for this instance
       when changes are made.
       Reimplemented from SoVRMLParent.

Member Data Documentation

   SoSFVec3f SoVRMLBillboard::axisOfRotation The axis of rotation for the geometry.
   SoSFVec3f SoVRMLBillboard::bboxCenter The bounding box center hint. Default value is (0, 0,
       0).
   SoSFVec3f SoVRMLBillboard::bboxSize The bounding box size hint. Default value is (-1, -1, -1).

Author

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