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Index › Programming Questions & Help › Programs › Simple "follow the mouse"
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Simple "follow the mouse" (Read 1926 times)
FayBee
Simple "follow the mouse"
Jan 29th, 2010, 2:05pm  
Hi!  I'm new to the forum, and fairly new to processing.

I'm trying to make a simple program where a "cannon's" (really a rectangle) barrel follows the mouse.  The cannon is supposed to be in a fixed position.  The problem that I'm finding is that the head doesn't follow the mouse fully until it gets to 45 degrees.  It jumps to that position when you put the mouse at 45.  It's hard to explain, and I apologize.  Here is the code:

float position;

void setup()
{
 size(400, 400);

}

void draw()
{
 background(255);
 noStroke();
 pushMatrix();
   if (mouseX > 0) {
 position = atan(-mouseY/mouseX);}
 else {
   position = (PI/2);}
 rotate(position);
 fill(0);
 rect(0, 0, 70, 40);
 popMatrix();
}


I hope someone can help me!

-FayBee
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TfGuy44
Re: Simple "follow the mouse"
Reply #1 - Jan 29th, 2010, 4:01pm  
Quote:
void setup()
{
  size(400, 400);
  rectMode(CENTER);
}

void draw()
{
  background(255);
  noStroke();
  pushMatrix();
  rotate(atan2(mouseY, mouseX));
  fill(0);
  rect(0, 0, 70, 40);
  popMatrix();
}
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FayBee
Re: Simple "follow the mouse"
Reply #2 - Jan 29th, 2010, 4:28pm  
THANK YOU SO MUCH! Smiley
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blindfish
Re: Simple "follow the mouse"
Reply #3 - Jan 30th, 2010, 1:38am  
TfGuy44 wrote on Jan 29th, 2010, 4:01pm:
Quote:
void setup()
{
  size(400, 400);
  rectMode(CENTER);
}

void draw()
{
  background(255);
  noStroke();
  pushMatrix();
  rotate(atan2(mouseY, mouseX));
  fill(0);
  rect(0, 0, 70, 40);
  popMatrix();
}



You know, if you really want to help people learn it's worth giving some kind of explanation for why something works.  In this case the key is the use of atan2 as opposed to atan.  For more info see this.
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Where is the what if the what is in why?
 
TfGuy44
Re: Simple "follow the mouse"
Reply #4 - Jan 30th, 2010, 7:39am  
Sometimes it's apparent that the person posting actually needs it explained to them. This was not one of those times. FayBee seemed to have a clear grasp of programming, and can clearly see the changes I made to the small amount of posted code

I do try to post a slightly more detailed answer if it is obvious that they need one. See, for example,  this, or this, or maybe even this.
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blindfish
Re: Simple "follow the mouse"
Reply #5 - Jan 30th, 2010, 9:54am  
Fair enough; though don't forget that other less experienced programmers might search the forums, come across this and have no idea why your code works Wink
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Where is the what if the what is in why?
 
Herschel
Re: Simple "follow the mouse"
Reply #6 - Feb 2nd, 2010, 4:22pm  
I was looking to do something very similar and this has helped. Thanks
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monicajones
Re: Simple "follow the mouse"
Reply #7 - Feb 3rd, 2010, 1:28am  
Thank you so much, i was about to make a topic asking about this too but you saved me the trouble and time. Smiley
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