Mapping angle

team_malenky

Hello

Am sure there is a simple solution to this but can't get my poor little head around it... Basically I am to get the angle of an object in relation to a central point. That part is fine...

The problem is the mapping of the rotation. It has 0 degrees at 9 O'clock and I need it to register 0 degrees at 6 O'clock. Little diagram and the code below, just pick up the ellipse and move around (angle outputting to console). Thanks for any help you can offer..

float centreX, centreY;

void setup() {

  size(600, 600);
  smooth();

  centreX = width/2;
  centreY = height/2;

  initChannels();
}

void draw() {

  background(200);

  noFill();
  ellipse(centreX, centreY, 20, 20);
  ellipse(centreX, centreY, 500, 500);


  //update objects
  for (int i = 0; i < channels.length; i++) {
    channels[i].update();
    channels[i].display();
  }
}

void mousePressed() {

  for (int i = 0; i < channels.length; i ++ ) {
    channels[i].mousePressed();
  }
}

void mouseDragged() {

  if (draggedObj != null) {
    draggedObj.mouseDragged();
  }
}

void mouseReleased() {

  draggedObj = null;
} 

//----------------------------------------------------//
//***** Object stuff *****//
//----------------------------------------------------//

int numChannels = 1; //number of channel objects to create
Channel[] channels;
Channel draggedObj;

void initChannels() {

  channels = new Channel[numChannels];
  for (int i = 0; i < channels.length; i++) {
    channels[i] = new Channel(i);
  }
}

class Channel {

  float x, y, w;
  float ang = random(360);
  float radius = random(200);

  Channel(int chan) {

    x = 150;
    y = centreY;
    w = 20;
  }

  void update() {

    //*** Work out angle and map to positive ***//
    ang = atan2(y - centreY, x - centreX);
    ang = degrees(ang);
    ang = map(ang, -180, 180, 0, 360);

  }

  void display() {

    fill(255);
    ellipse(x, y, w, w);
  }

  void mousePressed() {
    if (isMouseOver()) draggedObj = this;
  }

  void mouseDragged() {
    if (draggedObj != this) return;

    x = mouseX;
    y = mouseY;
    println(ang);
  }

  boolean isMouseOver() {
    return (mouseX > (x-w) & mouseX < (x+w) & mouseY > (y-w) & mouseY < (y+w));
  }

}

_vk

Hello, at first look I thought it should be easier than it turned out to be. I came up with a weird solution, probably stupid, but looks like it's working... Let's wait for better solutions, in meanwhile...

 //*** weird workaround to rotate coordinates ***//    

    // get angle to the desired position
    float temp_ang = atan2(y - centreY, x - centreX);

    //use it to plot the position one quarter forward in circle
    PVector shift = new PVector(cos(temp_ang+HALF_PI), sin(temp_ang+HALF_PI));

    //work with this position...
    ang = atan2(shift.y, shift.x);
    ang = degrees(ang);
    ang = map(ang, -180, 180, 0, 360);

team_malenky

Thank you _vk

Weird solution is working for me :) I know what you mean about appearing like a more simple problem, I had a feeling I was missing something really obvious. Maybe I still am...

Works well enough for what I need anyway so thanks.