Handling Object Picking

Listing 5 illustrates how to create, use, and dispose of pick objects. It defines a function, MyHandleClickInWindow , that takes a window pointer and an event record and handles mouse clicks in that window.

Listing 5 Picking objects

TQ3Status MyHandleClickInWindow (CGrafPtr myWindow, EventRec myEvent)
{
    TQ3WindowPointPickData          myWPPickData;
    TQ3PickObject                   myPickObject;
    unsigned long                   myNumHits;
    unsigned long                   myIndex;
    Point                           myPoint;
    TQ3Point2D                      my2DPoint;
    TQ3ViewObject                   myView;
    /*Get the window coordinates of a mouse click.*/
    SetPort(myWindow);
    myPoint = myEvent.where;                /*get location of mouse click*/
    GlobalToLocal(&myPoint);                /*convert to window coordinates*/
    my2DPoint.x = myPoint.h;                /*configure a 2D point*/
    my2DPoint.y = myPoint.v;
    /*Set up picking data structures.*/
    /*Set sorting type: objects nearer to pick origin are returned first.*/
    myWPPickData.data.sort = kQ3PickSortNearToFar;
    myWPPickData.data.mask = kQ3PickDetailMaskPickID | kQ3PickDetailMaskXYZ |
                                                    kQ3PickDetailMaskObject;
    myWPPickData.data.numHitsToReturn = kQ3ReturnAllHits;
    myWPPickData.point = my2DPoint;
    myWPPickData.vertexTolerance = 2.0;
    myWPPickData.edgeTolerance = 2.0;
    /*Create a new window-point pick object.*/
    myPickObject = Q3WindowPointPick_New(&myWPPickData);
    myView = MyGetViewFromWindow(myWindow);         /*increments reference count*/
    /*Pick a group object.*/
    Q3View_StartPicking(myView, myPickObject);
    do {
        Q3DisplayGroup_Submit(gGroup, myView);
    } while (Q3View_EndPicking(myView) == kQ3ViewStatusRetraverse);
    /*See whether any hits occurred.*/
    if (Q3Pick_GetNumHits(myPickObject, &myNumHits) == kQ3Failure || myNumHits==0) {
        Q3Object_Dispose(myPickObject);
        return;
    }
    /* Process each hit */
    for (myIndex = 0; myIndex = myNumHits; myIndex++) {
        TQ3Point3D      xyzPoint;
        unsigned long   pickID;
        TQ3Object       object;
        /* Get validMask first */
        if (Q3Pick_GetPickDetailValidMask(myPickObject, myIndex, &validMask)
                    == kQ3Failure) {
                break;
        }
        if (! ((validMask & kQ3PickDetailMaskXYZ) &&
                 (validMask & kQ3PickDetailMaskPickID) &&
                 (validMask & kQ3PickDetailMaskObject))) {
                continue;
        }
        /* Get world space intersection, pick ID, and geometry object reference */
        object = NULL;
        status = Q3Pick_GetPickDetailData (myPickObject, myIndex,
                                                kQ3PickDetailMaskXYZ, &xyzPoint);
        status = Q3Pick_GetPickDetailData (myPickObject, myIndex,
                                                kQ3PickDetailMaskPickID, &pickID);
        status = Q3Pick_GetPickDetailData (myPickObject, myIndex,
                                                kQ3PickDetailMaskObject, &object);
        /* Operate on xyzPoint, pickID, and object */
        ...
        if (object != NULL) {
                Q3Object_Dispose(object);
        }
    }
    /*Dispose of all hits in the hit list.*/
    Q3Pick_EmptyHitList(myPickObject);
    /*Dispose of the pick object.*/
    Q3Object_Dispose(myPickObject);
    /*Dispose of the view object.*/
    Q3Object_Dispose(myView);
}


Note that the call to Q3Pick_EmptyHitList is redundant, because disposing of a pick object (by calling Q3Object_Dispose ) also disposes of its associated hit list. The call is included in Listing 5 simply to illustrate how to call Q3Pick_EmptyHitList . You would, however, need to call to Q3Pick_EmptyHitList if you wanted to reuse the associated pick object in another pick operation.

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© 1997 Apple Computer, Inc.

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