pset4 ball won't move on click?

Question

I'm having some trouble getting the ball to move when the user clicks at the start of the game. I have the code below positioned in main, right after everything is instantiated, and before the while (true) loop. I created double xvel and double yvel global variables. When I run breakout, everything sets up correctly and the paddle follows my mouse, but the ball won't move on my click. Any help is appreciated. Thanks!

xvel = drand48();
yvel = - 2.0 * drand48();

GEvent start = getNextEvent(MOUSE_EVENT);    

if (start != NULL)
{
    if (getEventType(start) == MOUSE_CLICKED)
    {
        move(ball, xvel, yvel);
    }
}

Answer 1

Each instruction listed here will do each task exactly once. Translating your code into pseudo-code, it's doing roughly the following:

set xvel to a random number between 0 and 1
set yvel to a random number between -2 and -1

check if there is an event in the queue

if the event is a mouse click event then move the ball by the distance in xvel and yvel

This all happens once, before your loop.

There are two problems with this.

1. getNextEvent is intended to be used inside a loop. If you want to pause your program and wait for an event, you need to use waitForClick(). See the documentation for gevents!

2. Likewise, the move() statement only moves the object once, by a specified distance. To keep the object moving, you need to keep executing move() inside a loop. See the documentation for gobjects.