Post

Sensing Viewer Actions

Posted Updated
By CREATE3000
3 min read

Motivation

You can sense when the viewer’s cursor:

  • Is over a shape
  • Has touched a shape
  • Is dragging atop a shape

What can you do:

  • You can trigger animations on a viewer’s touch
  • You can enable the viewer to move and rotate shapes

Using action sensors

There are four main action sensor types:

The Anchor node is a special-purpose action sensor with a built-in response.

Sensing shapes

  • All action sensors sense all shapes in the same group
  • Sensors trigger when the viewer’s cursor touches a sensed shape

Syntax: TouchSensor

A TouchSensor node senses the cursor’s touch:

  • isOver - send true/false when cursor over/not over
  • isActive - send true/false when mouse button pressed/released
  • touchTime - send time when mouse button released

XML Encoding

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<Transform>
  <TouchSensor DEF='Touched'/>
  <Shape><!-- ... --></Shape>
  <!-- ... -->
</Transform>

Classic VRML Encoding

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Transform {
  children [
    DEF Touched TouchSensor { }
    Shape { ... }
    ...
  ]
}

A sample use of a TouchSensor node

XML Encoding

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<TouchSensor DEF='Touch'/>

<TimeSensor DEF='Timer1' ... />

<OrientationInterpolator DEF='Rot1' ... />

<Transform DEF='Frame1'
  <Shape><!-- ... --></Shape>
</Transform>

<ROUTE fromNode='Touch' fromField='touchTime' toNode='Timer1' toField='set_startTime'/>
<ROUTE fromNode='Timer1' fromField='fraction_changed' toNode='Rot1' toField='set_fraction'/>
<ROUTE fromNode='Rot1' fromField='value_changed' toNode='Frame1' toField='set_rotation'/>

Classic VRML Encoding

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DEF Touch TouchSensor { }

DEF Timer1 TimeSensor { ... }

DEF Rot1 OrientationInterpolator { ... }

DEF Frame1 Transform {
  children [
    Shape { ... }
  ]
}

ROUTE Touch.touchTime         TO Timer1.set_startTime
ROUTE Timer1.fraction_changed TO Rot1.set_fraction
ROUTE Rot1.value_changed      TO Frame1.set_rotation

Syntax: SphereSensor

A SphereSensor node senses a cursor drag and generates rotations as if rotating a ball:

  • isActive - sends true/false when mouse button pressed/released
  • rotation_changed - sends rotation during a drag

XML Encoding

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<Transform>
  <SphereSensor DEF='Rotator'/>
  <Transform DEF='RotateMe'><!-- ... --></Transform>
</Transform>
<ROUTE fromNode='Rotator' fromField='rotation_changed' toNode='RotateMe' toField='set_rotation'/>

Classic VRML Encoding

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Transform {
  children [
    DEF Rotator  SphereSensor { }
    DEF RotateMe Transform { ... }
  ]
}
ROUTE Rotator.rotation_changed TO RotateMe.set_rotation

Syntax: CylinderSensor

A CylinderSensor node senses a cursor drag and generates rotations as if rotating a cylinder:

  • isActive - sends true/false when mouse button pressed/released
  • rotation_changed - sends rotation during a drag

XML Encoding

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<Transform>
  <CylinderSensor DEF='Rotator'/>
  <Transform DEF='RotateMe'><!-- ... --></Transform>
</Transform>
<ROUTE fromNode='Rotator' fromField='rotation_changed' toNode='RotateMe' toField='set_rotation'/>

Classic VRML Encoding

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Transform {
  children [
    DEF Rotator  CylinderSensor { }
    DEF RotateMe Transform { ... }
  ]
}
ROUTE Rotator.rotation_changed TO RotateMe.set_rotation

Syntax: PlaneSensor

A PlaneSensor node senses a cursor drag and generates translations as if sliding on a plane:

  • isActive - sends true/false when mouse button pressed/released
  • translation_changed - sends translations during a drag

XML Encoding

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<Transform>
  <PlaneSensor DEF='Mover'/>
  <Transform DEF='MoveMe'><!-- ... --></Transform>
</Transform>
<ROUTE fromNode='Mover' fromField='translation_changed' toNode='MoveMe' toField='set_translation'/>

Classic VRML Encoding

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Transform {
  children [
    DEF Mover  PlaneSensor { }
    DEF MoveMe Transform { ... }
  ]
}
ROUTE Mover.translation_changed TO MoveMe.set_translation

Using multiple sensors

Multiple sensors can sense the same shape but …

If sensors are in the same group:

  • They all respond

If sensors are at different depths in the hierarchy:

  • The deepest sensor responds
  • The other sensors do not respond

Summary

Action sensors sense when the viewer’s cursor:

  • is over a shape
  • has touched a shape
  • is dragging atop a shape

Sensors convert viewer actions into events to:

  • Start and stop animations
  • Orient shapes
  • Position shapes

Animation, Sensors, and Geometry

Tutorials
Sensing Viewer Actions
This post is licensed under CC BY 4.0 by the author.