Processing exercise, Need HELP!

[MrWhite117]

im 1st year mmu games design student and im stuck on this exercise, all i'm trying to do is get this ball to bounce around the screen and ive gotten so far but not sure how to proceed any suggestions.

the ball keeps disappearing.

//bouncing ball

float x; //ball x position
float dx = 3; //ball x direction is right, step 5
float y; //ball y position
float dy = 3;

void setup () //runs once at start
{
size(500, 250);
}

void draw() //runs repeatedly
{
background(0); //black
stroke(255, 0, 0); //pen red
fill(255, 255, 0); //yellow
ellipse(x, y, 10, 10);
x = x + dx; //move ball x right
y = y + dy; //move ball y

//Collision detection
//collide right hand edge?
if (x>=500)
dx = -dx; //reverse x direction

else if (y>=250)
dy = -dy;

else if (x<=-500)
dx = +dx;

else if (y<=-250)
dy = +dy;
}

[SurfMan]

I am not familiar with the framework this runs in, but is it really neccessary to set the background all the time? It looks like it's a race between the ball and the background.

Other than that, you might want to take the width of the ball into account for the right hand edge. It bounces at x >= 500, but I assume the base coordinate of the ball is its top left. You would then want to bounce at x >= 500 - width_of_the_ball. Same for the bottom.

[Norm]

Can you make a small complete program that compiles, executes and shows the problem?

Be sure to wrap your code with code tags:
[code]
YOUR CODE GOES HERE
[/code]
to get highlighting and preserve formatting.

[KevinWorkman]

This is Processing, so this actually *is* an SSCCE/MCVE.

And yeah, setting the background like that is correct. It's just clearing the previous frame.

Anyway, you have two problems that I see:

First, the y value of the top of the window is 0, but you're trying to bounce your ball off of y value -250, which is above the top of the window.

Secondly, this doesn't do what you think it does:

dy = +dy;

You might be looking for an absolute value function here? If you're confused about what I'm saying, set up a little example program that uses the println function to print out the value of dy after the above line.

[SurfMan]

T
First, the y value of the top of the window is 0, but you're trying to bounce your ball off of y value -250, which is above the top of the window.

Secondly, this doesn't do what you think it does:

dy = +dy;

Good catch!

[MrWhite117]

I am not familiar with the framework this runs in, but is it really neccessary to set the background all the time? It looks like it's a race between the ball and the background.

Other than that, you might want to take the width of the ball into account for the right hand edge. It bounces at x >= 500, but I assume the base coordinate of the ball is its top left. You would then want to bounce at x >= 500 - width_of_the_ball. Same for the bottom.

thank you for the help but i figured it out in the end.

[KevinWorkman]

thank you for the help but i figured it out in the end.

"When you do things right, people won't be sure you've done anything at all..."