Thread: Need help with motion direction

There is a simple trigonometric relationship between the angle and the x/y velocity of the projectile. I would suggest reading Projectile motion - Wikipedia, the free encyclopedia.

It really boils down to a few equations:

The ball's initial x and y velocity is this:

Vx_0 = V * cos(theta)
Vy_0 = V * sin(theta)

where theta is the angle in radians and V is the magnitude of the velocity (a.k.a. it's speed).

To convert between degrees to radians, multiply degrees by pi/180.

If you haven't already, I would strongly recommend taking algebra and geometry at the very least. These classes will help you understand the basic math concepts such as vectors and angles.

If you take physics I, it will help you to add gravity and collision detection/rebound to your game.

Gravity is quite simple:
Basically, as time goes on, Vy decreases.

Vy = -g * t + Vy_0

Collisions/rebound is harder, but doable provided you have the math/physics background (basic classes listed above).

I understand the equations, the only problem is I don't understand how I would implement it. I will be using a Timer class to determine the speed at which the ball moves, how would I implement this in my code? what would be incremented.

Example,
int angle = 45;
int vel = 10; // milliseconds
int velX = vel * cos(angle * (Math.PI / 180));
int velY = vel * sin(angle * (Math.PI / 180));

Timer time = new Timer(vel, new TimerListener());
timer.start();

class TimerListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
// What do I enter here?
// This is to shoot the ball
}
}

Originally Posted by Sayco

I understand the equations, the only problem is I don't understand how I would implement it. I will be using a Timer class to determine the speed at which the ball moves, how would I implement this in my code? what would be incremented.

Example,
int angle = 45;
int vel = 10; // milliseconds
int velX = vel * cos(angle * (Math.PI / 180));
int velY = vel * sin(angle * (Math.PI / 180));

Timer time = new Timer(vel, new TimerListener());
timer.start();

class TimerListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
// What do I enter here?
// This is to shoot the ball
}
}

You're keeping track of the projectile's position, correct? At a given time step, simply keep updating it's position (this is a numerical integration).

position.x = position.x + velX * time_step
position.y = position.y + velY * time_step

setFocusable() should only allow you to focus a component, not transfer the focus to that component.

I'm not positive on the focus system in Java, but I believe calling requestFocusInWindow() will transfer the input focus to the component you want.

If it does not, I would suggest reading How to Use the Focus Subsystem (The Java™ Tutorials > Creating a GUI With JFC/Swing > Using Other Swing Features)