The Model-View-Controller Architecture - Essentials of Interactive Computer Graphics - page 136

void CModel::UpdateSimulation() { Source file. Model.cpp

file in the Model folder of the
D3D _ BallShoot project.

// compute elapsed second since previous update
float elapsed _ seconds = ...

//check for collisions between all of the existing balls
foreach test _ ball in m _ AllBalls
foreach other _ ball in m _ AllBalls
if (test _ ball.Intersects(other _ ball)) // if the two balls intersect
// computer new velocities for both
// detail description can be found in Section B.1

// not shown code identical to Listing 5.24 (Tutorial 5.5 )

}

Listing 5.25. CModel::UpdateSimulation() function (Tutorial 5.6).

Figure 5.11 is a screenshot from interacting with the ball-shooting program im-
plemented in Tutorial 5.6. When comparing to Tutorial 5.5 we notice two major

differences: interball collision and slider-bar control of ball velocity.

Figure 5.11. Tutorial

5.6.

Interball Collision

In order to compute interball collision, we must collide each ball with every other
ball in the world. Listing 5.25 shows the nested for loops required to compute in-
tersections between every ball in the world. Notice that this is an O

n 2 operation,

where n is the number of balls in the m _ AllBalls array. As the number of balls
increases in the world, this collision routine would quickly cause sub-real-time
responses. In this case, because the user must click and drag to create a ball and
because balls free fall out of the application window rapidly, the total number of
balls in the m _ AllBalls array does not grow very large (e.g., less than 100). For
these reasons, we can still experience real-time response.

( )

Slider-Bar Controls

As discussed in Tutorial 2.3, if registered, MFC will call the OnHScroll() func-
tion for servicing of the horizontal scroll bar events. Listing 5.26 shows that the
servicing of the scroll-bar events involves setting the velocity of the currently se-
lected ball. In this case, the user changes the selected ball velocity in between
timer events, and during the servicing of timer event the UpdateSimulation()
function will move the selected ball by its new velocity. Notice that the Update
Simulation() and OnHScroll() functions will never execute concurrently.