Event-Driven Programming - Essentials of Interactive Computer Graphics - page 27

// Left mouse button up service routine
D3: LMBUpRoutine (mousePosition)
InsertHeroBallToAllWorldBalls()
DefiningNewHeroBall = false

// Right mouse button down service routine
D4: RMBDownRoutine (mousePosition)
HeroBall = SelectHeroBallBasedOn (mousePosition )
if (HeroBall != null) SetSliderBarsWithHeroBallVelocity()

// Slider Bar change service routine
D5: SliderBarRoutine (sliderBarValues)
if (HeroBall != null)
SetSliderBarsWithHeroBallVelocity(sliderBarValues)

// Timer expired service routine
D6: ServiceTimer ()
// Move balls by velocities and remove off-screen ones

UpdateSimulation()

// Sets status bar with number of balls on screen
EchoToStatusBar()

// Generates a redraw event
GUISystem :: GenerateRedrawEvent

// Reflect propoer HeroBall velocity
if (HeroBall != null)
SetSliderBarsWithHeroBallVelocity(sliderBarValues)

// Redraw event service routine
D7: RedrawRoutine ()
DrawBalls(AllWorldBalls)
if (DefiningNewHeroBall)
// Draw the new Hero Ball that is being defined
DrawBalls(HeroBall)

Listing 1.7. (cont.)

The timer event definition (A2S2) sets up a periodic alarm for the application
to update the simulation of the free-falling balls. The service routines of the
user-generated application-specific events (D1-D5) are remarkably similar to the