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atan2 (Read 364 times)
odin4000
atan2
Feb 26th, 2009, 10:07pm  
Hi,
We know that atan2 function calculate the angle of the mouse in the range of {-PI,PI} but in my knob i need to get the angle from -5*PI/4 to PI/4 or relative angles.
Here is my code:

float radius = 100;
float angle = -5*PI/4;
float x = 200, y = 200;
void setup() {
 size(400,400);
 ellipseMode(CENTER);
 smooth();
}
void draw() {
background(100);
fill(255);
ellipse(x,y,radius,radius);
fill(0,0,255);
 arc(x,y,radius,radius,-5*PI/4,angle);
fill(0);
 arc(x,y,radius,radius,PI/4,3*PI/4);
fill(50);
 strokeWeight(5);
 ellipse(x,y,radius/2,radius/2);
}
void mouseDragged() {
if(mouseX >= x-radius/2 && mouseX <= x+radius/2 && mouseY >= y-radius/2 && mouseY <= y+radius/2) {
angle = atan2(mouseY-y,mouseX-x);
}
}
void mouseReleased() {
if(mouseX >= x-radius/2 && mouseX <= x+radius/2 && mouseY >= y-radius/2 && mouseY <= y+radius/2) {
angle = atan2(mouseY-y,mouseX-x);
}
}
Thanks for helping me,
Odin
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koogy
Re: atan2
Reply #1 - Feb 26th, 2009, 11:35pm  
add the following under your angle = atan2() calls (both of them)

Code:

  if (angle > (PI * .75) && angle < PI) {
    angle = angle - TWO_PI;
  }


it basically remaps that last PI/4 bit that you couldn't access before from the values it gives to the values you want. (i must confess it was largely guesswork. and i converted it all to degrees and then back again. that'll get me thrown out of trig school...)
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odin4000
Re: atan2
Reply #2 - Feb 26th, 2009, 11:46pm  
Thanks you very much! This trig was making me crazy Tongue

Oh, an other thing can anyone explain how to make the knob block once he arrive at PI/4 angle?
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koogy
Re: atan2
Reply #3 - Feb 28th, 2009, 5:04pm  
er. isn't PI / 4 your highest value? then isn't it simply

if (angle > PI / 4) {
 angle = PI / 4;
}

(do this after the other code from the last answer as those values are > PI / 4 before modification)

the thing i worry about is that with a single knob on screen (a nice knob, but only one) i was getting 100% processor usage on my laptop. i guess setting a framerate would help (at the cost of responsiveness)
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