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Index › Programming Questions & Help › Syntax Questions › Trigonometric knob

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Trigonometric knob (Read 1863 times)

odin4000

Trigonometric knob
Feb 24^th, 2009, 9:40pm

hi,
im creating a knob wich would increment with the when you dragged on it. I made a simple ellipse with a line to take it easy, and now im stuck with the atan2 and my mouse coordinate... i know about radians and trigonometric laws but when i try it the angle is given by my atan2 does not correspond with the angle i need... The other thing i wasn't sure about it if i should use a mousePressed or a mouseDragged function because i need it to update when i click on it too. anyway.. here is my code, have a look please;

float px,py;
float radius = 100;
float angle = 0;
float x = 200, y = 200;
void setup() {
size(400,400);
ellipseMode(CENTER);
}
void draw() {
px = x + cos(degrees(angle))*(radius/2);
py = y + sin(degrees(angle))*(radius/2);
ellipse(x,y,radius,radius);
line(x,y,px,py);
}
void mouseDragged() {
if(mouseX >= x-radius/2 && mouseX <= x+radius/2 && mouseY >= y-radius/2 && mouseY <= y+radius/2) {
angle = atan2(mouseY,mouseX);
}
}

Thanks for answers,
Odin

NoahBuddy Ex Member	Re: Trigonometric knob Reply #1 - Feb 24^th, 2009, 10:08pm Replace "degreees(angle)" with just "angle". Sin() and Cos() accept radians as input. Also, atan2 needs to be offset by the center of your circle: angle = atan2(mouseY-y, mouseX-x); Oh, and to do the same when clicking, just copy from mouseDragged() to mouseReleased().

odin4000 YaBB Newbies Offline Posts: 13	Re: Trigonometric knob Reply #2 - Feb 24^th, 2009, 10:29pm Thanks you very much it work great and you replied fast

bmud

Re: Trigonometric knob
Reply #3 - Feb 26^th, 2010, 3:31pm

Hello. I'm having a similar problem where I want the angle added to the knob to be relative (because, let's face it, making it absolute is silly)

However, like all functions based on tangent, there's an asymptote at -PI and +PI. This makes things rather annoying if you cross over the boundary between the bottom left corner to the top right corner.

How does one handle free movement so that you can just keep rotating any way you want?

Code:

float angle = PI;

void setup(){
  size(300,300);
  smooth();
}

void draw(){
  background(200);
  noFill();
  strokeWeight(1);
  ellipse(width/2, height/2, 200,200);
  fill(255);
  strokeWeight(6);
  arc(width/2, height/2, 200,200, 0, angle);
  pushMatrix();
    translate(width/2, height/2);
    rotate(angle);
    line(0,0,100,0);
  popMatrix();
}

void mouseDragged(){
  float thisAngle = atan2(mouseY-height/2, mouseX-width/2);
  float prevAngle = atan2(pmouseY-height/2, pmouseX-width/2);
  angle += thisAngle - prevAngle;
  println(angle);
}

(by the way, i realize that the arc can't render in negatives, so don't worry about that. I'm more concerned for the angle value getting messed up)

subpixel Senior Member Offline Posts: 261	Re: Trigonometric knob Reply #4 - Feb 27^th, 2010, 12:29am The "angle" seems fine; it is more the number of revolutions that seems the problem. Do you really mean for the knob values to forever increase (or decrease), or instead always represent a value within a single revolution? Try this: Code: angle = (angle + thisAngle - prevAngle + TWO_PI) % TWO_PI; -spxl
	Processing: subpixels.com, OpenProcessing.org \| VJ portfolio: SPXL.TV

subpixel

Re: Trigonometric knob
Reply #5 - Feb 27^th, 2010, 12:45am

To allow looping, try something like this:

Code:

void mouseDragged(){
  float thisAngle = atan2(mouseY-height/2, mouseX-width/2);
  float prevAngle = atan2(pmouseY-height/2, pmouseX-width/2);
  float diff = thisAngle - prevAngle;
  println("diff: " + diff);
  if (diff >= PI)
  {
    diff -= TWO_PI;
    println("Big positive diff corrected to: " + diff);
  }
  else if (diff <= -PI)
  {
    diff += TWO_PI;
    println("Big negative diff corrected to: " + diff);
  }

  angle += diff;
  println("New angle: " + angle);
}

-spxl

Processing: subpixels.com, OpenProcessing.org | VJ portfolio: SPXL.TV

subpixel

spxlSuperKnob
Reply #6 - Feb 27^th, 2010, 7:45am

After more than a little tweaking...

A new SuperKnob class to play with!

OpenProcessing link: spxlSuperKnob

A GUI knob that allows multiple revolutions.

Features:

Rotation limited to specified number of revolutions in each direction
Revolutions marker with graduated colour indicator
Snap to full revolutions (visual cue: changed marker colours)
Plays well with other knobs (ie doesn't hog mouseDragged())
Resizable

Howzat

-spxl

Processing: subpixels.com, OpenProcessing.org | VJ portfolio: SPXL.TV

bmud YaBB Newbies Offline Posts: 24 NC	Re: Trigonometric knob Reply #7 - Feb 28^th, 2010, 10:26pm FANCY! Thanks subpixel. You're the freaking man.
	« Last Edit: Mar 1^st, 2010, 6:05pm by bmud »

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