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Some questions about moving circles from beginner (Read 599 times)

check2010

Some questions about moving circles from beginner
Feb 9^th, 2010, 5:35pm

My questions are in the code:

//Declaring two variables to act as my x-coordinates for my two circles.
int x1=50;
int x2=750;

void setup() {
size(800,600);
}

void draw() {
background(50);

noStroke();
ellipse(x1,300,50,50);
ellipse(x2,300,50,50);

x1=x1+1;
x2=x2-1;

//I'll make an if-statement to turn the circles red when their x-coordinates are the same. Is typing in the two ellipse functions necssary?
if (x1==x2) {
noStroke();
fill(125,0,0);
ellipse(x1,300,50,50);
ellipse(x2,300,50,50);
}
}

/*I'm wanting a line to be created whenever the mouse is clicked. This happens, yet it disappears right after I see it on the screen. I know
this is because my draw function keeps repeating. One solution is to put my background function in to setup(), yet then my two circles leave
a trail. How do I fix this? */
void mousePressed() {
strokeWeight(4);
stroke(255);
line(400,50,400,250);
}

-------------------------------------------------------------------------

My second question is about trying to create a program that moves a ball back and forth on the screen.

int x1=50;

void setup() {
size(800,600);
}

void draw() {
background(75);

ellipse(x1,300,80,80);
x1=x1+3;

if (x1==750) {
x1=x1-6;
}
}

//This seems to me like it would work. I'm sending the ball from x=50 to x=750 and trying to get it back again. How do I achieve this?

Thanks very much!

TfGuy44

Re: Some questions about moving circles from beginner
Reply #1 - Feb 9^th, 2010, 5:50pm

Part 1. See comments in code. Comments about the line are numbered.

Quote:

int x1=50;
int x2=750;

// 1) Define a global boolean to track if the mouse was ever pressed.
boolean mouseWasClicked = false;

// 2) When the mouse is pressed...
void mousePressed() {
  mouseWasClicked = true; // 3) Update the boolean to remember that fact.
}

void setup() {
  size(800,600);
}

void draw() {
  background(50);

  noStroke();
  ellipse(x1,300,50,50);
  ellipse(x2,300,50,50);

  x1=x1+1;
  x2=x2-1;

  if (x1==x2) {
    noStroke();
    fill(125,0,0); // The fill color will stay red until you change it again.
    ellipse(x1,300,50,50); // This will cover up both of them in the instance when they overlap.
    // ellipse(x2,300,50,50); // But there's no need to draw a second one here. They're at the same place.
    // And this block of code is only ever executed ONCE.
  }

  if( mouseWasClicked){ // 4) If the mouse was pressed...
    strokeWeight(4);
    stroke(255);
    line(400,50,400,250); // 5) draw the desired line.
  }

}

TfGuy44

Re: Some questions about moving circles from beginner
Reply #2 - Feb 9^th, 2010, 5:56pm

Part 2.

Quote:

int x1=50;

void setup() {
size(800,600);
}

void draw() {
background(75);

ellipse(x1,300,80,80);

x1=x1+3; // x1 starts at 50, then 53, 56, 59, 62, ...
// eventually it gets to 746, 749, 752...

if (x1==750) { // But it never EQUALS 750!
x1=x1-6; // this line never executes, as the condition is never met.
}

if (x1 > 750) { // Even with the right condition,
x1=x1-6; // this still isn't going to do what you want.
} // Run it and see!

// I'll post some code showing you how you can do it next. Hold on.

}

TfGuy44

Re: Some questions about moving circles from beginner
Reply #3 - Feb 9^th, 2010, 6:02pm

Part 2, working.

Quote:

int x1 = 50;
int x_step = 3; // A new variable that determines how much x1 changes.

void setup() {
  size(800,600);
}

void draw() {
  background(75);
  ellipse(x1, 300, 80, 80);
  x1 = x1 + x_step; // This line is important. Look.

  if (x1 > 750) { // when we get close to the right side...
    x_step = -3; // change direction!
  }

  if (x1 < 50) { // and when we get close to the left side...
    x_step = 3; // change direction again!
  }

}

check2010 YaBB Newbies Offline Posts: 43 Illinois, USA	Re: Some questions about moving circles from beginner Reply #4 - Feb 9^th, 2010, 6:22pm Thanks TfGuy! I feel like a dummy about the whole x1 never being 750 thing. Haha. I'll be sure to review this code a lot until I fully grasp it

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