3D Graphics Programming with QuickDraw 3D 1.5.4

Picking in Immediate Mode

Picking IDs are particularly useful when picking in immediate mode. Listing 7 shows how to create a triangle, attach a picking ID to it, and then process hits.

Listing 7 Picking in immediate mode



 
void MyImmediateModePickID (TQ3ViewObject view, WindowPtr window)

{

    TQ3WindowRectPickData               myPickData;

    TQ3TriangleData                     myTriangleData;

    TQ3PickObject                       myPick;

    TQ3ViewStatus                       myViewStatus;

    unsigned long                       pickID;

    Rect                                myPortRect;

    Point                               myCenter;

    unsigned long                       myNumHits;



 
    /*Set up a triangle.*/

    Q3Point3D_Set(&myTriangleData.vertices[0].point, -1.0, -0.5, 0.0);

    Q3Point3D_Set(&myTriangleData.vertices[1].point,  1.0,  0.0, 0.0);

    Q3Point3D_Set(&myTriangleData.vertices[2].point, -0.5,  1.5, 0.0);

    myTriangleData.vertices[0].attributeSet = NULL;

    myTriangleData.vertices[1].attributeSet = NULL;

    myTriangleData.vertices[2].attributeSet = NULL;

    myTriangleData.triangleAttributeSet = NULL;



 
    /*Set up TQ3WindowPointPickData structure.*/

    myPickData.data.sort = kQ3PickSortNone;

    myPickData.data.mask = kQ3PickDetailMaskPickID | kQ3PickDetailMaskObject;

    myPickData.data.numHitsToReturn = kQ3ReturnAllHits;



 
    myPortRect = ((GrafPtr) window)->myPortRect;

    myCenter.h = (myPortRect.right  - myPortRect.left)/2.0;

    myCenter.v = (myPortRect.bottom - myPortRect.top) /2.0;



 
    Q3Point2D_Set(&myPickData.rect.min, myCenter.h - 5, myCenter.v - 5);

    Q3Point2D_Set(&myPickData.rect.max, myCenter.h + 5, myCenter.v + 5);



 
    /*Create the window rectangle window pick.*/

    myPick = Q3WindowRectPick_New(&myPickData);



 
    /*Submit the pick ID and triangle in immediate mode.*/

    Q3View_StartPicking(view, myPick);

    do

    {

        Q3PickIDStyle_Submit(kPickID, view);

        Q3Triangle_Submit(&myTriangleData, view);

        myViewStatus = Q3View_EndPicking(view);

    } while (myViewStatus == kQ3ViewStatusRetraverse);



 
    Q3Pick_GetNumHits(myPick, &myNumHits);

    if (numHits == 1)

    {

        /*Get the pickID data (for first and only hit) and check if it's 

            the expected pick ID.*/

        Q3Pick_GetPickDetailData(myPick, 0);

        if (pickID == kPickID)

        {

            /*picked on triangle with pick ID*/

        }

    }



 
    Q3Object_Dispose(myPick);

}