# How to fix the positions of lines (Math related)

**URL:** https://discourse.processing.org/t/how-to-fix-the-positions-of-lines-math-related/27344
**Category:** Project Guidance
**Created:** [January 24, 2021, 9:16pm UTC](https://discourse.processing.org/t/how-to-fix-the-positions-of-lines-math-related/27344 "2021-01-24T21:16:25Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![CodeMasterX](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/codemasterx/32/2942_2.png) [@CodeMasterX](https://discourse.processing.org/u/CodeMasterX)
#### Post date: [January 24, 2021, 9:16pm UTC](https://discourse.processing.org/t/how-to-fix-the-positions-of-lines-math-related/27344/1 "2021-01-24T21:16:25Z")

</div>

![image](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/2X/0/0f30685c74b41eb5237185b65cec2b1e61a13c5b.png)

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/2X/1/16e45be44b43e607511208cb710bb4624e66998b.png)  
(I am trying to do this with a n-sided shape)  
but it is not working. The program works by having a position of the corner and giving a `dir` and `r`. How do I get the correct position? The current program only works for `n = 6`

> **Code**
>
> ```auto
> ArrayList<line> lines = new ArrayList<line>();
> float v = 0, speed = 0.01, n = 6;
> void setup() {
> size(600,600);
> float a = TWO_PI/n, cx = 300, cy = 300, nr = 200, nr2 = dist(cos(0)*nr,sin(0)*nr,cos(a)*nr,sin(a)*nr);
> for(int i = 0; i < n; i++) {
> float nx = cx+cos(a*i)*nr, ny = cy+sin(a*i)*nr;
> lines.add(new line(nx,ny,a*(i-1),-nr2));
> }
> //lines.add(new line(100,100,0,400));
> //lines.add(new line(500,100,PI/2,400));
> //lines.add(new line(500,500,PI,400));
> //lines.add(new line(100,500,PI*1.5,400));
> background(0);
> } 
> void draw() {
> for(int i = 0; i < lines.size(); i++) {
> lines.get(i).display();
> }
> noFill();
> beginShape();
> for(int i = 0; i < lines.size()+1; i++) {
> PVector vertexPos = lines.get(i%lines.size()).getPos(v);
> vertex(vertexPos.x,vertexPos.y);
> }
> endShape();
> v+=speed;
> if(v >= 1 || v<=0) { speed*=-1; background(0); }
> }
> class line {
> float x, y, dir, r;
> line(float x1_, float y1_, float dir_, float r_) {
> x = x1_;
> y = y1_;
> dir = dir_;
> r = r_;
> }
> void display() {
> stroke(255);
> float nx = x + cos(dir)*r, ny = y + sin(dir)*r;
> line(x, y, nx, ny);
> }
> PVector getPos(float v) {
> return new PVector(x + cos(dir)*r*v, y + sin(dir)*r*v);
> }
> }
> 
> ```

---

<div class="post-metadata">

### Author: ![Chrisir](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/chrisir/32/45_2.png) [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [January 24, 2021, 9:45pm UTC](https://discourse.processing.org/t/how-to-fix-the-positions-of-lines-math-related/27344/2 "2021-01-24T21:45:35Z")

</div>

```auto
ArrayList<LineClass> lines = new ArrayList<LineClass>();
float n = 7;

void setup() {
  size(600, 600);
  background(0);

  float a = TWO_PI/n, 
    cx = 300, cy = 300, 
    nr = 200;

  for (int i = 0; i < n; i++) {
    float nx = cx+cos(a*i)*nr, ny = cy+sin(a*i)*nr;
    lines.add(new LineClass(nx, ny, 
      cx+cos(a*(i+1))*nr, ny = cy+sin(a*(i+1))*nr) );
  }
} 

void draw() {
  background(0);

  for (LineClass lc : lines) {
    lc.display();
  }
}

// ==========================================================================

class LineClass {

  float x1, y1, 
    x2, y2;

  LineClass(float x1_, float y1_, 
    float x2_, float y2_) {
    x1 = x1_;
    y1 = y1_;

    x2 = x2_;
    y2 = y2_;
  }

  void display() {
    stroke(255);
    line(x1, y1, x2, y2);
  }
  //
}//class
//

```