Package com.openinventor.inventor.nodes

Class SoBillboard

  • All Implemented Interfaces:
    SafeDisposable
    public class SoBillboard
extends SoSeparator
    Grouping node that modifies its coordinate system so that its local Z-axis always points at the viewer. The SoBillboard 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 children of an SoBillboard node may include other grouping nodes as well as shape nodes.

    Performance:

    • SoBillboard nodes recompute the screen alignment transformation on every render traversal. A large number of billboard nodes will reduce performance.
    • The orientation of an SoBillboard depends on the current camera settings, so this node should not be render cached.
    • SoBillboard nodes prohibit auto-caching, so no SoSeparator (or other render caching node) above an SoBillboard in the scene graph will automatically create a render cache. This can significantly reduce performance and applications should put nodes that can be render cached (especially geometry nodes) under their own SoSeparator below the SoBillboard.
    • We recommend leaving the useSphereBBox field set to true.
      This will significantly improve performance when using billboard nodes.

    Export limitations:

    • SoBillboard can be exported to PDF3D/U3D (SoToPDFAction) as a group node, but due to limitations of that file format, it will not act as a billboard. In other words, the geometry will not be "screen locked".

    The axisOfRotation field specifies which axis to use to perform the rotation. This axis is defined in the local coordinates of the SoBillboard node. The default (0,1,0) is useful for objects such as images of trees and lamps positioned on a ground plane. But when an object is oriented at an angle, for example, on the incline of a mountain, then the axisOfRotation may also need to be oriented at a similar angle.

    A special case of billboarding is screen-alignment the object rotates to always stay aligned with the viewer even when the viewer elevates, pitches and rolls. This special case is distinguished by setting the axisOfRotation to (0, 0, 0).

    To rotate the SoBillboard to face the viewer, determine the line between the SoBillboard's origin and the viewer's position; call this the billboard-to-viewer line. The axisOfRotation and the billboard-to-viewer line define a plane. The local z-axis of the SoBillboard is then rotated into that plane, pivoting around the axisOfRotation.

    If the axisOfRotation and the billboard-to-viewer line are coincident (the same line), then the plane cannot be established, and the rotation results of the SoBillboard are undefined. For example, if the axisOfRotation is set to (0,1,0) (Y-axis) and the viewer flies over the SoBillboard and peers directly down the Y-axis the results are undefined .

    Multiple instances of SoBillboards (DEF/USE) operate as expected - each instance rotates in its unique coordinate system to face the viewer.

    File format/default:

    Billboard {

      axisOfRotation 0 1 0
      useSphereBBox true
    }

    Since:
    Open Inventor 10.0

    • Field Detail

      • axisOfRotation

        public final SoSFVec3f axisOfRotation
        Specifies which axis to use to perform the rotation.

      • useSphereBBox

        public final SoSFBool useSphereBBox
        Specifies if the bounding box returned by SoBillboard.getBoundingBox() method should be extended to completely contain the bounding sphere of the children. This hint avoids bounding box cache breaks due to rotation of the billboard geometry (which changes the default axis aligned bounding box) and provides a significant performance increase when many SoBillboard nodes are used.

        Default is true

    • Constructor Detail

      • SoBillboard

        public SoBillboard()
        Constructor.

      • SoBillboard

        public SoBillboard​(int nChildren)
        Constructor that takes approximate number of children.