Chapter 3: Node Reference--The Annotated VRML97 Reference Manual

PlaneSensor { exposedField SFBool autoOffset TRUE exposedField SFBool enabled TRUE exposedField SFVec2f maxPosition -1 -1 # (-

) exposedField SFVec2f minPosition 0 0 # (-

) exposedField SFVec3f offset 0 0 0 # (-

) eventOut SFBool isActive eventOut SFVec3f trackPoint_changed eventOut SFVec3f translation_changed }

The PlaneSensor node maps pointing device motion into two-dimensional translation in a plane parallel to the Z=0 plane of the local coordinate system. The PlaneSensor node uses the descendent geometry of its parent node to determine whether it is liable to generate events.

TIP: It is usually a bad idea to route a drag sensor to its own parent. Typically, the drag sensor will route to Transform, which does not affect the sensor. See the following examples.

TECHNICAL NOTE: A PlaneSensor that is not oriented almost perpendicular to the viewer can be very difficult to control. Small movements of the pointer can result in very large translations, because the plane and the pointing ray are almost parallel. The specification is a little bit vague about what to do about such cases, guaranteeing only that the trackPoint will accurately represent the last intersection of the pointing ray with the plane. Implementations are left free to experiment with schemes to control the translation_changed events that are generated to make it easier for users to control.

TIP: Combining PlaneSensor with other features produces some neat features. Putting a PlaneSensor underneath a Billboard node results in a PlaneSensor that always turns to face the user, which can make a user interface component built from a PlaneSensor much easier to control. Combining a PlaneSensor, ProximitySensor, and a Transform node can result in a PlaneSensor that is always in front of the user. Again, this can be very useful, since one big problem with user interface controls in a 3D world is that it is easy for the user to lose them. Combining these two techniques can give you a PlaneSensor that is always in front of the user and is always oriented with the computer screen. In that case, the PlaneSensor will produce values that are almost raw mouse x, y positions (almost because the positions will be off by constant scale and offset factors).

EXAMPLE (click to run) : The following example illustrates a simple case of the PlaneSensor node (see Figure 3-43). It uses three PlaneSensors to translate a Cone in a restricted rectangular area. Notice how the Transforms are used to rotate the PlaneSensors into the XY plane (since the default orientation for a PlaneSensor is the XY plane). The second two PlaneSensors illustrate how to create 1D sliders by taking advantage of the minPosition and maxPosition fields:

#VRML V2.0 utf8Group { children [  Transform {           # Create the object to be xlated    translation 0 1 0    rotation 1 0 0 1.57 # Rotate sensor into XZ plane    children [      DEF PS1 PlaneSensor {        minPosition -5 -5        maxPosition 5 5      }      DEF T1 Transform {        rotation 1 0 0 -1.57 # unrotate cone upright        children Shape {          appearance DEF A1 Appearance {            material Material { diffuseColor 1 1 1 }          }          geometry Cone { bottomRadius 1 height 2 }        }      }    ]  }  Transform {          # Create Z slider    translation 5 0 0     rotation 1 0 0 1.57    children [      DEF PS2 PlaneSensor {        minPosition 0 -5    # Restrict xlation to Z axis        maxPosition 0 5      }      DEF T2 Transform {    # Z Slider's thumb geometry        children Shape {          geometry Box { size .5 .5 .5 }          appearance USE A1        }      }    ]  }  Transform {          # Create X slider    translation 0 0 -5     rotation 1 0 0 1.57    children [      DEF PS3 PlaneSensor {        minPosition -5 0    # Restrict xlation to X axis        maxPosition 5 0      }      DEF T3 Transform {    # X Slider's thumb geometry        children Shape {          geometry Cylinder { radius 0.5 height 1 }          appearance USE A1        }      }    ]  }  Transform {               # table    translation 0 -0.1 0    children Shape {      geometry Box { size 10 0.2 10 }      appearance USE A1    }  }  Background { skyColor 1 1 1 }  NavigationInfo { type "EXAMINE" }]}ROUTE PS1.translation_changed TO T1.set_translationROUTE PS2.translation_changed TO T2.set_translationROUTE PS2.translation_changed TO T1.set_translationROUTE PS3.translation_changed TO T3.set_translationROUTE PS3.translation_changed TO T1.set_translationROUTE PS2.offset_changed TO PS1.set_offsetROUTE PS3.offset_changed TO PS1.set_offset

3.34 PlaneSensor

Figure 3-42: PlaneSensor Node

Figure 3-43: PlaneSensor Example