help - moving things on an angle

[Raknarg]

It's simple. He adds or subtracts one to the x and y values. If it hits a wall, the x direction or y direction is multiplied by -1. That way it switches direction every time it hits a wall.

[Tony]

Because you can work with:
- velocity_x, velocity_y
or
- velocity, angle
Those are two different ways to represent the same information.

[whoareyou]

So in pseudo-code:

1) draw the ball (0,0)

2) add "x" to the xposition of the ball

3) +/- "y" to the yposition of the ball

4) If the ball hits the boundary, multiply current x by -1

[Raknarg]

You can do it without trig, but there's some cases where you'd want to use it. For instance, if your just moving a ball around the screen linearly, there's probably no reason to use trig.

[Tony]

Right. This assumes horizontal/vertical walls and incoming_angle = outgoing_angle (for collisions). Which works well enough for simple pong. Anything beyond those assumptions will require trig.

[whoareyou]

Java:

int x, y, w, h, vx, vy, timer;         x = (int) (Math.random () * c.maxx () - 10);         y = (int) (Math.random () * c.maxy () - 10);         w = (int) (Math.random () * c.maxx () / 2);         h = w;         vx = (int) (Math.ceil (Math.random () * 20));         vy = (int) (Math.ceil (Math.random () * 20));         timer = 5;         c.setColor (Color.black);         c.fillOval (x, y, w, h);         while (true)         {             x += vx;             y += vy;             if (x < 0 || x >= c.maxx () - w)             {                 vx *= -1;             }             if (y < 0 || y >= c.maxy () - h)             {                 vy *= -1;             }             c.fillOval (x, y, w, h);             Thread.sleep (timer);             c.clear ();         }

Except sometimes it gets stuck at the bottom and I don't know why. I tried subtracting 10 from the x and y coordinates so they don't get stuck, but that doesn't seem to fox the problem.

[whoareyou]

I've run into another issue. Now, when I run my program, the ball bounces around for sometime and then eventually gets stuck in the paddle. What I've done what assign the y-values of the front face of the paddle to an array and it checks it will touch the paddle - if so, then the ball will reflect. But it gets stuck in the paddle after a couple of bounces.

Java:

int x, y, w, h, vx, vy, timer;         x = c.maxx () / 2;         y = c.maxy () / 2;         w = 50;         h = w;         vx = 5;         vy = 5;         int x2, y2, w2, h2;         x2 = 0;         y2 = 124;         w2 = 30;         h2 = 250;         timer = 5;         c.setColor (Color.black);         c.fillOval (x, y, w, h);         c.fillRect (x2, y2, w2, h2);         int[] horizontal = new int [x2 + w2 + 1];         int[] vertical = new int [h2 - y2 + 1];         for (int i = 0 ; i < horizontal.length ; i++)         {             horizontal [i] = i;         }         int start = y2;         for (int i = 0 ; i < vertical.length ; i++)         {             vertical [i] = start;             start++;         }         while (true)         {             x += vx;             y += vy;             for (int i = 0 ; i < vertical.length ; i++)             {                 if (vertical [i] < y && x < w && y < h2)                 {                     vx *= -1;                     break;                 }             }             if (x < 0 || x >= c.maxx () - w)             {                 vx *= -1;             }             else if (y < 0 || y >= c.maxy () - h)             {                 vy *= -1;             }             c.fillOval (x, y, w, h);             c.fillRect (x2, y2, w2, h2);             Thread.sleep (timer);             c.clear ();         }