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19.1.2 ObjectPickMapper class

The pick engine is truly only an engine; it does not handle or generate any events. Event generation is, instead, the duty of the ObjectPickMapper class, which converts input movement and drags into target object picks, including "no target" picks. The picking itself is handled through delegation to a PickEngine object configured with the desired pick root and target list. Both continuous and discrete picking modes are supported. For continuous picking, pick events are reported only when the target object changes, and not when the pick cursor moves, which helps to keep event handling overhead to a minimum.

Picking modes

To accommodate various flavors of discrete and continuous picking, several methods are provided. These methods affect only the mode of pick reporting for input drag events. Continuous pick reporting, as a result of input movement events, is not affected by these modes. The different modes can be combined, with the result being an ORing of object pick events. The setDoPick method specifies that the pick tar-get is reported when a drag starts, and no target is reported when the drag stops. This is the default mode. The setDoDrag method specifies that the pick target is reported only when the drag starts, which is useful for triggering the drag portion of a drag-and-drop operation. The setDoDrop method specifies that the pick target is reported continuously during the drag, and when the drag stops, which is useful for tracking drop targets.

ObjectPickTarget interface

Pick reporting requires a new event interface. The ObjectPickTarget interface reports both the pick index and the pick object. In general, the pick index should be used if the event target has knowledge of the pick engine's target list, because it uniquely identifies the object in the list (and the object reference may not). If the event target is not privy to the target list, or if the pick event originates from a pick process that does not use a list, then the pick object must be used. It is important to keep these alternative uses of the event in mind when generating or handling ObjectPickTarget events because some event targets use one or the other exclusively. As with all other framework events, the event has a corresponding ObjectPickSplitter class.

19.1.3 OverEnableMapper class

Knowing which object was picked using a pick engine and an object pick mapper is only two thirds of the solution when it comes to mouseover object control. The framework provides the last third of the solution in the form of the OverEnableMapper class. To use this class, you have to create a list of control targets that implement the EnableTarget interface, with a one-to-one correspondence between the event targets in this list and the pick targets in the pick engine's target list, such as that used by an ObjectPickMapper object. When a new target is picked, as indicated by the input ObjectPickTarget event interface, any previous enable target is disabled and the one corresponding to the new pick is enabled. Note that OverEnableMapper uses only the index parameter in its input event interface.

For convenience, two special-purpose control targets can be set in addition to, or in lieu of, the event list targets. The setEventTargetAny method establishes an enable target that is notified when any target is picked; the setEventTargetNone method establishes an event target that is notified when no target is picked.

19.1.4 Example: OverEnabling

This example demonstrates object picking and mouseover enabling of control inputs.

See
The virtual world contains four target objects: three in a central column (red, green, blue) and one to the right (magenta). A screen shot is provided in figure 19. 2.

Do

• Drag the mouse (left button with SHIFT) in the display or use the arrow keys (with SHIFT) to orbit the view in heading and elevation about the world origin.
• Drag the mouse (left button) on the top (red) target or use the ARROW keys to translate it along the world X-Y axes.
• Drag the mouse (left button) on the middle (green) target or use the ARROW keys to rotate it about the world Y axis.
• Drag the mouse (left button) on the bottom (blue) target or use the ARROW keys to scale it along the world x-y axes.
• Drag the mouse (left button) on the right (magenta) target or use the ARROW keys to roll the target like a trackball.
• Repeat the drag operations from different view directions.

Observe

• All target operations use mouseover to enable the operation.
• Target picking can differentiate between parent (green thing) and child (magenta thing) in the scene graph.
• All target operations use the first mouse button and no MODIFIER keys.
• All coordinate mapping is static, meaning that manipulation of targets will seem nonintuitive if the view is not head-on.

The general structure of the code for this example is similar to that in the previous example, which demonstrated actuator groups, but with one important difference. In this example, the utility building block buildOverEnabler from the IntuitiveBlocks class is used to perform overenabling of the target actuators. The first code sample below is from the OverEnabling example class. It shows those portions that deal with the translation target and overenabling. The second sample is from the utility class. It shows how the utility building block combines the framework's core building blocks for picking with move and drag sensors into a single convenient module for overenabling.

...
// setup manipulation targets 
/// translation target 
AffineGroup affineXlt= new AffineGroup( new TestThing( 
TestThing.BOX_TRANSLATION, TestThing.BALL_DEFAULT)); 
getWorld().addSceneNode(BasicBlocks.buildTarget( 
affineXlt, new Vector3d( 0, 3, 0))[ 0]); 
... 
// setup manipulation controls 
InputDragMapper mapper; 

/// translation, first button 
mapper = ActuationBlocks.buildDirectMapper( 
  affineXlt.getTranslation(), new Vector2d(. 025, .025), 
  Mapper.DIM_X, Mapper.DIM_Y, true); 

ActuationBlocks. buildRelativeDragger( mapper, 
  getView(), Input.BUTTON_FIRST, 
  Input.MODIFIER_NONE, Input.MODIFIER_NONE); 
... 
// setup over management 
ArrayList pickList, enableList; 

pickList= new ArrayList(); 
pickList.add( affineXlt); 
pickList.add( sphere); 
pickList.add( affineRot); 
pickList.add( affineScl); 

enableList = new ArrayList(); 
enableList.add( <affineXlt); 
enableList.add( sphere); 
enableList.add( affineRot); 
enableList.add( affineScl); 

IntuitiveBlocks. buildOverEnabler( getView(), 
getWorld().getSceneRoot(), >pickList, enableList); 
... 

	
... 
/** 
Creates mouse move and drag sensors, an object picker, and 
an over enabler and connects them together for continuous 
target picking and enabling, whether during mouse movement 
or dragging. All enable targets will be initialized as if 
no target was picked. 
@param view Source display. 
@param pickRoot Scene graph pick root. 
@param pickList List of pick targets. 
@param enableList List of enable targets corresponding to 
the targets in the pick list. 
*/ 
public static final OverEnableMapper buildOverEnabler( 
 AppView view, BranchGroup pickRoot, ArrayList pickList, 
 ArrayList enableList) { 

	// setup over target enabling 
	OverEnableMapper enabler = new OverEnableMapper(); 
enabler.setEventTargets(enableList); 

enabler.initEventTargets(-1); 

// setup continuous target picking 
ObjectPickMapper picker = new ObjectPickMapper( enabler, 
 new PickEngine( pickRoot, pickList)); 

/// generate mouse position for any move or drag 
MouseDragSensor dragger = new MouseDragSensor( picker, 
 view.getDisplay(), view.getRoot()); 
dragger.setButtons( Input.BUTTON_ALL); 

MouseMoveSensor mouseMove = new MouseMoveSensor( 
 picker, view.getDisplay(), view.getRoot()); 

return enabler; 
} 
... 

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