I created code of a ball bouncing off 4 walls. When I mousePress; the ball accelerates.

The problem is, the ball doesn't continue and accelerate in the same direction. It seems to slow down and change direction.

I think it is because the variable "acceleration" adds a positive number to the negative variable "speed", leading to some undesirable movements.

Can anyone explain to me what is going on and how to straighten the trajectory? Thanks.

Here is the code.

boolean on = false;
float x = 16;
float y = 16;
float xspeed = 3;
float yspeed = 2;
float acceleration = 0.2;

void setup() {
 size(200,200);
}

void draw() {
background(255);

fill(150);
stroke(0);
ellipse(x,y,32,32);

x = x + xspeed;
y = y + yspeed;

if (on) {
 xspeed = xspeed + acceleration; yspeed = yspeed + acceleration;
}

if (mousePressed){
on = !on;
}

if ((x > width - 16) || (x < 16)) {
 xspeed = xspeed * -1;
}

if ((y > height - 16) || (y < 16)) {
 yspeed = yspeed * -1;
}
}

Thanks. That improved the result.

Also I will use velocity instead of speed when defining direction.