Hierarchical Modeling - Essentials of Interactive Computer Graphics - page 314

void CDrawAndMouseHandler::OnMouseButton( bool down, unsigned int nFlags, int hwX, int hwY)
// variable for point in DC space

A:

int dcX, dcY;

Source file.
DrawAndMouseHandler.cpp
file

// variable for point in WC space
float wcX, wcY;
// Transform from hardware space (hwX,hwY) to DC (dcX, dcY)

in the WindowHan-

dlers folder of the

D3D _ SceneNodePicking
project.

B: HardwareToDevice(hwX, hwY, dcX, dcY);

// Transform from DC (dcX,dcY) to WC (wcX,wcY)
DeviceToWorld(dcX, dcY, wcX, wcY);

if (MK _ LBUTTON && down) // if left mouse button is clicked
// Calls the PickNodeAt() function with mouse click in WC
theApp.GetModel().PickNodeAt(wcX,wcY)

C:

Listing 11.17. The mouse-click service routine of Tutorial 11.7.

get pSearchNode . In this way, the bbox returned will be the WC bounding box of
the currently selected scene node. Because all positions are in the WC space, we
can perform the simple containment test at label D to determine if pick _ point is
within the bounds of bbox . Listing 11.17 shows the mouse event service routine
implemented in CDrawAndMouseHandler.cpp . In this case, we can see that the
mouse-click position is forwarded to the service routine in hardware coordinate
space, ( hwX , hwY ) . At label B, the mouse-click position is transformed into DC

space, . At label C, we see that

when the left mouse button is clicked, the CModel::PickNodeAt() function is
called with the mouse-click position in the WC space.

( dcX , dcY ) , and then to WC space, ( wcX , wcY )

11.4.2 Collision

In Section 7.5, we discussed the issues involved with colliding primitives. Our
conclusion is that it is more efficient to approximate collisions with intersections
of simple volumes that bound the colliding primitives. The UWB _ BoundingVolume
class (Listing 7.15 on p. 185) was introduced to approximate primitive collision.
In the previous section, we learned how to compute WC bounding boxes for scene
node objects based on the UWB _ BoundingBox class to support mouse-click selec-
tion. We can now approximate the collision between scene nodes based on the
intersection of their corresponding bounding boxes.

Tutorial 11.8.
Project Name:
D3D _ SceneNodeCollision
Library Support:
UWB_MFC_Lib1
UWB_D3D_Lib12

Tutorial 11.8. Collision Detection

• Goal. Demonstrate colliding scene node objects based on the WC bounding
boxes.